Limited Field-of-View Cone Beam CT Imaging

of the Temporomandibular Joints:

Comparative Dosimetry and Diagnostic Efficacy

by

Tricia Dawn Lukat

A thesis submitted in conformity with the requirements

for the degree of Master of Science in Oral and Maxillofacial Radiology

Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry

University of Toronto

© Copyright by Tricia Dawn Lukat 2013

ii

Limited Field-of-View Cone Beam CT Imaging of the Temporomandibular Joints:

Comparative Dosimetry and Diagnostic Efficacy

Tricia Dawn Lukat

Master of Science in Oral and Maxillofacial Radiology

Discipline of Oral and Maxillofacial Radiology, Faculty of Dentistry University of Toronto

2013

Abstract

Imaging of the osseous structures of the temporomandibular joint is best accomplished

using computed tomography (CT). Cone beam CT offers a reduced radiation dose and

improved spatial resolution compared to multislice helical CT. This study evaluates

comparative dosimetry for temporomandibular joint imaging using two different cone

beam CT systems, the Hitachi CB MercuRay and Kodak 9000 3D. These systems

demonstrate differing properties with respect to field-of-view sizes, operational technique

factors, and spatial resolution. The Kodak 9000 3D unit offers an effective radiation

dose reduction of greater than ten-fold compared with the Hitachi CB MercuRay,

depending on kVp and mA. A subsequent clinical study evaluating the effect of spatial

resolution on the ability to detect osseous changes related to temporomandibular joint

degenerative disease found no significant difference in diagnostic efficacy between high

and low spatial resolution images, however, observers consistently associated high

spatial resolution with superior image quality.

iii

Acknowledgements

Thank you to my supervisor, Dr. Ernest Lam, for inspiring my interest in Oral and

Maxillofacial Radiology. Your support throughout these last three years has been

unending and deeply appreciated, and you motivate me to strive for excellence in

everything that I do.

Dr. Michael Pharoah, you have taught me to respect both the science and the art of this

specialty, and I will be forever honored to be one of your students.

Special thanks to Drs. Susanne Perschbacher, Milan Madhavji, and Ernest Lam, for the

countless hours spent reviewing images of temporomandibular joints.

To Drs. Michael Pharoah, Marie Dagenais, David Mock, Robert Wood, and Howard

Tenenbaum, for your time, support, and guidance as members of my thesis committee.

Jason (“Bongo”) Wong, my Summer 2012 Sidekick, your meticulous work on the

comparative dosimetry project will never be forgotten.

Thank you to my co-residents for assisting me with patient recruitment for the clinical

component of this study.

And finally, to my husband and best friend Dean, whose selflessness, understanding, and

encouragement made this entire experience possible.

iv

Table of Contents

Abstract............................................................................................................................... ii

Acknowledgements ........................................................................................................... iii

Table of Contents............................................................................................................... iv

List of Tables ................................................................................................................... viii

List of Figures.................................................................................................................... ix

List of Appendices.............................................................................................................. x

Chapter 1: Introduction....................................................................................................... 1

1.1 Evolution of temporomandibular joint imaging .................................................. 1

1.1.1 Hard tissue imaging ........................................................................... 1

1.1.2 Soft tissue imaging ............................................................................ 3

1.2 Ionizing radiation and patient radiation dose....................................................... 4

1.2.1 Biological effects of ionizing radiation ............................................. 4

1.2.2 Principles of radiation protection for diagnostic imaging ................. 4

1.2.3 Comparative dosimetry...................................................................... 5

1.3 Image quality ....................................................................................................... 6

1.3.1 Contrast resolution............................................................................. 6

1.3.2 Spatial resolution ............................................................................... 7

1.3.2.1 CT image geometry ............................................................ 7

1.3.2.2 Nyquist limitation and sampling frequency........................ 8

1.3.2.3 Detector element size.......................................................... 8

1.3.2.4 Image reconstruction filter.................................................. 9

1.3.3 Prior research on spatial resolution and diagnostic efficacy ............. 9

v

1.4 Diagnostic imaging of the temporomandibular joints ....................................... 10

1.4.1 Patient selection criteria................................................................... 10

1.4.2 Goals ................................................................................................ 10

1.4.3 Choice of imaging modality ............................................................ 11

1.5 Degenerative joint disease ................................................................................. 12

1.5.1 Pathophysiology .............................................................................. 12

1.5.2 Structural changes............................................................................ 12

1.5.3 Diagnostic imaging.......................................................................... 13

1.6 Statement of the problem ................................................................................... 14

1.6.1 Comparative dosimetry.................................................................... 14

1.6.2 Image quality ................................................................................... 15

1.7 Aim .................................................................................................................... 16

1.8 Objectives .......................................................................................................... 17

1.9 Hypotheses ......................................................................................................... 18

1.9.1 Primary hypotheses.......................................................................... 18

1.9.2 Null hypotheses ............................................................................... 18

Chapter 2: Materials and Methods.................................................................................... 19

2.1 Part A: Comparative dosimetry ......................................................................... 19

2.1.1 Overview ......................................................................................... 19

2.1.2 Materials for dosimetric measurements........................................... 20

2.1.3 Imaging techniques.......................................................................... 20

2.1.4 Dosimetry calculations .................................................................... 22

2.1.5 Statistical analysis............................................................................ 23

2.2 Part B: Voxel size and diagnostic efficacy ........................................................ 28

2.2.1 Overview ......................................................................................... 28

2.2.2 Ethics approval ................................................................................ 28

vi

2.2.3 Equipment modifications required for clinical use.......................... 28

2.2.3.1 Modified chin support ...................................................... 29

2.2.3.2 Estimation of subject intercondylar distance.................... 29

2.2.4 Study design .................................................................................... 30

2.2.4.1 Inclusion criteria ............................................................... 30

2.2.4.2 Exclusion criteria .............................................................. 30

2.2.4 Image processing and downsampling.............................................. 31

2.2.5 Image analysis ................................................................................. 31

2.2.6 Statistical analyses ........................................................................... 32

Chapter 3: Results............................................................................................................. 39

3.1 Part A: Comparative dosimetry ......................................................................... 39

3.2 Part B: Voxel size and diagnostic efficacy ........................................................ 41

Chapter 4: Discussion ....................................................................................................... 47

4.1 Part A: Comparative dosimetry ......................................................................... 47

4.1.1 Hitachi CB MercuRay versus Kodak 9000 3D dosimetry .............. 47

4.1.2 Translating exposure to risk ............................................................ 51

4.1.3 Kodak 9000 3D technique factor modulation.................................. 52

4.1.4 Future directions in comparative dosimetry research...................... 54

4.2 Part B: Voxel size and diagnostic efficacy ........................................................ 55

4.2.1 Effect of voxel size on detection of osseous changes...................... 55

4.2.2 Effect of voxel size on perceived image quality.............................. 57

4.2.3 Study limitations.............................................................................. 57

4.2.4 Drawbacks of limited field-of-view imaging .................................. 60

4.2.5 Practical considerations ................................................................... 60

vii

Chapter 5: Conclusions..................................................................................................... 62

References ........................................................................................................................ 63

Appendices ....................................................................................................................... 71

viii

List of Tables

Table 1. Anatomical correlates of optically stimulated luminescence (OSL) dosimeters in

RANDO® man anthropomorphic phantom...................................................................... 26

Table 2. Effective tissue dose calculation factors............................................................. 27

Table 3. Mean effective tissue doses and total effective doses with respective standard

deviation values for each of the temporomandibular joint imaging modalities and

technique settings ............................................................................................................. 40

Table 4. Fleiss’ kappa for interobserver reliability........................................................... 42

Table 5. Cohen’s kappa for intraobserver reliability ........................................................ 43

Table 6. Radiographic feature identification results based on the McNemar !2 test for

paired groups .................................................................................................................... 44

Table 7. Effect of voxel size on visual analog scale (VAS) responses by observers based

on a paired samples t-test.................................................................................................. 45

ix

List of Figures

Figure 1. Left lateral view of the anthropomorphic RANDO® man phantom ................ 24

Figure 2. Sample optically stimulated luminescence (OSL) dosimeter placement at level

4 of the anthropomorphic RANDO® man phantom to measure absorbed dose for the lens

and orbit of the right and left eye ..................................................................................... 25

Figure 3. Modified chin support used during patient positioning for Kodak 9000 3D

temporomandibular joint imaging .................................................................................... 34

Figure 4. Caliper tool used for estimation of subject intercondylar distance ................... 35

Figure 5. Kodak acquisition modular software medio-lateral crosshair positioning guide

based on estimated subject intercondylar distance ........................................................... 36

Figure 6. Correct subject positioning within the Kodak 9000 3D cone beam CT unit for

temporomandibular joint imaging .................................................................................... 37

Figure 7. Downsampling technique applied to a temporomandibular joint image volume

acquired using the Kodak 9000 3D cone beam CT system.............................................. 38

Figure 8. Visual analog scale (VAS) ratings of image quality for the overall average from

all observers, as well as from each observer independently, for the 76µm and 300µm

voxel sizes......................................................................................................................... 46

Figure 9. Native Hitachi CB MercuRay cone beam CT temporomandibular joint images

(panoramic mode, 0.290mm) compared to Kodak 9000 3D images downsampled to

300µm using the anthropomorphic RANDO® man phantom.......................................... 59

x

List of Appendices

Appendix 1. Landauer specification sheet for InLight® nanoDot™ dosimeters ............. 71

Appendix 2. Health Sciences Research Ethics Board approval letter .............................. 73

Appendix 3. Patient information and consent forms ........................................................ 74

Appendix 4. Observer calibration PowerPoint exercise ................................................... 82

Appendix 5. Sample observer score sheet for identification of radiographic features and

visual analog scale ............................................................................................................ 86

Appendix 6. Translating exposure to risk: calculations.................................................... 87

!

1

Chapter 1

1 Introduction

1.1 Evolution of Temporomandibular Joint Imaging

Diagnostic imaging of the temporomandibular joint has evolved significantly since its

inception. Advances in imaging technology have allowed for progressive improvements

in visualization of both osseous and soft tissue components of this joint.

1.1.1 Hard Tissue Imaging

The fundamental osseous structures of interest in temporomandibular joint imaging

consist of the mandibular condyle, glenoid fossa, and articular eminence. Two-

dimensional planar views were the initial modalities used to radiographically evaluate

hard tissue structures of the temporomandibular joint, and multiple orthogonal views

were acquired to emphasize different aspects of the complex joint anatomy. Transcranial

and transpharyngeal views provide lateral profile views of the temporomandibular joint,

and preferentially depict the lateral and medial aspects of the condyle, respectively. To

avoid excessive superimposition of the joint anatomy with the adjacent skull base,

transcranial and transpharyngeal views both required a degree of obliquity and thus did

not provide an accurate representation of the condylar-fossa relationship. The open

mouth transorbital view provides a frontal view of the condyle, free from

superimposition by the articular eminence, and the open Townes view portrays a similar

depiction of the condylar neck region. Despite the compilation of information from

multiple radiographic views, superimposition of overlying anatomical structures hindered

detection of subtle osseous changes within the temporal and condylar joint components,

thereby rendering significant diagnostic limitations (1).

Panoramic radiography is a specialized application of tomography, in which objects lying

within a horseshoe-shaped focal trough are clearly portrayed while objects outside this

2

region appear blurred and are not well imaged. The temporomandibular joints are

located within this focal trough, and panoramic imaging is often used as a preliminary

tool to assess patients presenting with joint related complaints. However, this technique

has several shortcomings, including inaccuracies in representation of joint position,

anatomical superimpositions, poor spatial resolution, image distortion, and views limited

to the lateral and central regions of the condyle. Although modern panoramic units offer

specialized protocols for temporomandibular joint imaging, there is no evidence that this

confers a diagnostic advantage for detection of osseous abnormalities (2). Only gross

pathological changes are readily and reliably demonstrated by panoramic imaging

techniques.

The advent of conventional tomography enabled a solution to the issue of overlapping

anatomical structures associated with the use of traditional planar and panoramic views.

Conventional tomography uses the technique of motion blurring to render objects located

outside of the focal plane relatively “invisible” compared to the object of interest, which

is centrally positioned within the focal plane. The generation of thin orthogonal cross-

sectional slices permits visualization of all aspects of the joint structures, with negligible

effects of superimposed anatomy. Studies have demonstrated that use of sagittal and

coronal tomographic views render superior diagnostic accuracy compared to panoramic

radiography in the detection of osseous temporomandibular joint changes (3,4).

Computed tomography (CT) applies mathematical algorithms to digitally acquired

projection data to completely remove overlying structures, as opposed to simply blurring

them out as with conventional tomography. The first documented use of CT imaging to

evaluate the temporomandibular joint was in 1978 by Wegener et al. (5), and this

technique is now accepted as the imaging modality of choice to visualize osseous

structures of the temporomandibular joint (6,7). More recently, the introduction of cone

beam CT has provided an alternative imaging modality to assess hard tissue structures of

the joint, with a purported reduction in radiation dose to the patient and superior image

quality compared to multislice helical CT (8,9). Prior research also suggests that the

diagnostic accuracy of cone beam CT is significantly greater than that of panoramic

3

imaging and conventional linear tomography for detection of cortical erosions involving

the temporomandibular joints (2).

1.1.2 Soft Tissue Imaging

While the aforementioned imaging modalities provide information about the osseous

structures of the temporomandibular joint, no details are provided regarding the articular

disc or its associated attachments. Although CT images with soft tissue algorithms were

investigated as a potential tool to evaluate the disc, the specificity is poor and this

approach is no longer endorsed (10). Arthrography was the first technique utilized to

provide indirect visualization of the disc through coupling of radiography, fluoroscopy,

or tomography with the injection of iodinated contrast media into the superior and/or

inferior joint spaces. Due to the invasive nature of the procedure and accompanying

discomfort for the patient, this imaging approach has been largely replaced by the use of

magnetic resonance (MR) imaging. Unlike the previously mentioned imaging

modalities, MR does not involve the use of ionizing radiation, but rather utilizes a strong

magnetic field and radiofrequency energy to generate images. MR imaging provides

superior soft tissue contrast to all other imaging modalities, and can directly demonstrate

the articular disc. Acquisition of both closed and open mouth views gives information

about the position, shape, and integrity of the articular disc, and allows for assessment of

internal derangements. While MR imaging provides some information about the osseous

structures of the joint, autopsy studies demonstrate that the sensitivity and specificity of

detecting osseous changes by MR imaging is inferior to that provided by CT imaging

(0.50 and 0.71 for MR versus 0.75 and 1.00 for CT) (10). It is generally accepted that

both the sensitivity and specificity parameters should exceed a value of 0.70 for a

temporomandibular joint imaging examination to be considered clinically useful (11).

Consequently, CT and MR are typically regarded as complementary imaging modalities.

4

1.2 Ionizing Radiation and Patient Radiation Dose

1.2.1 Biological Effects of Ionizing Radiation Planar imaging, panoramic radiography, conventional tomography, and CT (both

multislice helical and cone beam) all utilize ionizing radiation to produce diagnostic

images. Through primarily free radical-mediated interactions with biological

macromolecules, ionizing radiation is capable of causing cellular damage. Most of the

deleterious effects of ionizing radiation arise due to DNA damage, which may result in

lethal, cell-killing effects or sublethal genetic changes. At radiation doses used in

diagnostic imaging, sublethal effects are the primary concern. Sublethal DNA damage

may be resolved by intrinsic repair mechanisms, or may persist and potentially result in

carcinogenesis depending on the particular gene or genes involved. Carcinogenesis is

classified as a stochastic effect of radiation, in which the event probability increases

proportional to dose, but the severity is unaffected. There is no “threshold dose” for

stochastic effects of radiation; technically, a single x ray photon is capable of causing

DNA damage and evoking the subsequent chain of events (12). Because of the known

risk associated with the use of ionizing radiation, strict radiation protection practices

must be applied to diagnostic imaging procedures. While these conservative concepts

are refuted by some critics due to potential inaccuracies when the effects of high dose

radiation exposure are extrapolated to the much lower doses used during diagnostic

imaging, the burden of proof ultimately requires adherence to the most cautious radiation

protection protocols.

1.2.2 Principles of Radiation Protection for Diagnostic Imaging

While no maximum dose limits are established for diagnostic exposure of patients, the

principles of justification and optimization endorsed by both the National Council on

Radiation Protection (NCRP) and the International Commission on Radiological

Protection (ICRP) are recognized aspects of responsible radiology practice. The

principle of justification states that the health benefit to the patient outweighs any

potential risk conferred by radiation exposure, thereby acknowledging that the risks of

5

diagnostic imaging are low but not zero, as per the linear no-threshold dose-response

model. All radiographic examinations are considered prescriptions, and should be

ordered following a thorough history and clinical examination. The concept of

optimization is predicated on the ALARA (“as low as reasonably achievable”) principle,

with economic and social factors taken into account. While initially developed for

occupational radiation protection, this doctrine can and should be applied to patient

imaging so that exposure techniques are optimized to minimize patient dose while

maintaining diagnostic image quality. Modification of technique factors, the application

of appropriate views and imaging volumes, and use of protective barriers such as leaded

aprons and thyroid collars whenever possible are all imperative and modifiable measures

that reduce patient radiation dose (12,13).

1.2.3 Comparative Dosimetry

Numerous studies have evaluated the relative dose burden imparted upon patients by

various diagnostic imaging procedures involving the craniofacial region. Particular

attention has focused around comparative dosimetry of multislice helical CT versus cone

beam CT (8,14,15,16,17,18). The average effective dose for an adult head CT

examination is approximately 2000 microsieverts (µSv) (19). Adapting a specific

temporomandibular joint protocol to multislice helical CT through field-of-view

limitation, the effective dose is reduced to about 600µSv (20). Although it is generally

accepted that cone beam CT examinations render a lower radiation dose to patients, there

is immense variability in dose depending on the particular cone beam CT system being

used. Reported effective doses from various cone beam CT units range from 5.3µSv for

a limited field-of-view examination of the anterior maxilla using a Kodak 9000 3D unit

(21) to 1073µSv for a 12-inch field-of-view acquisition of the craniofacial complex,

using a Hitachi CB MercuRay unit operating at 120kVp and 15mA (8). The field-of-

view size, operating technical factors such as voltage (kVp), current (mA), and exposure

time, as well as use of a continuous or pulsed x ray beam all contribute to radiation dose

variability of different cone beam CT units (1,8). A study by Palomo et al. (22)

demonstrated an overall dose reduction of approximately 0.62 times (38%) when

6

reducing the operating voltage of the Hitachi CB MercuRay cone beam CT system from

120kVp to 100kVp, with all other technique factors held constant. It was also

demonstrated that reducing the field-of-view from 12-inches to 6-inches results in a

decrease in absorbed dose to tissues remaining within the primary x ray beam by about

5% to 10%, which is likely the result of diminished scatter radiation produced by field-

of-view restriction. Tissues and organs outside of the primary beam field experience a

significant reduction in absorbed dose values (up to 95%). While the use of cone beam

CT clearly offers an inarguable dose profile advantage over multislice helical CT, there is

significant latitude for optimization of patient dose by modification of imaging

parameters within specific cone beam CT systems.

Although the vast majority of comparative dosimetry studies involving cone beam CT

imaging are published in the oral and maxillofacial literature, the medical community is

also beginning to consider lower dose options to the traditional CT systems. Ruivo et al.

(23) describe the use of an i-CAT cone beam CT unit for in vivo postoperative imaging

of cochlear implants. Comparative dosimetry assessment revealed an effective dose of

80µSv for the i-CAT technique, compared to 3600µSv for a 16-slice CT and 4800µSv

for a 4-slice CT unit. In addition to a significant radiation dose reduction, the cone beam

CT images also demonstrated less metallic artifacts from the cochlear implant electrodes

and an overall improvement in perceived image quality.

1.3 Image Quality

While dose is an important factor to consider when exposing a patient to ionizing

radiation, other parameters such as image quality and subsequent diagnostic efficacy

must also be implicitly considered. Contrast resolution and spatial resolution are the two

fundamental determinants of image quality (19).

1.3.1 Contrast Resolution

Contrast resolution is defined as the ability to detect subtle changes in grayscale and

distinguish this from background noise in the image (19). Noise is determined by the

7

number of x ray photons reaching the detector; the more photon interactions per detector

element, the better the signal-to-noise ratio of the resulting image. Technique factors are

key determinants of contrast resolution, and include voltage (kVp), current (mA), and

exposure time for both multislice helical and cone beam CT. Increasing any of these

factors results in improved contrast resolution through an increased number of photon-

detector interactions and a greater signal-to-noise ratio, but this occurs at the expense of

increased patient dose. In multislice helical CT, a pitch value of less than one (defined as

the ratio of gantry movement distance to nominal slice thickness) improves contrast

resolution by decreasing image noise, but again at the cost of increasing dose. Greater

slice thickness in multislice helical CT improves contrast resolution by increasing the

number of detected photons per detector element and in turn reduces image noise. The

reconstruction filter applied to multislice helical CT also impacts contrast resolution;

application of a ramp filter with roll-off at high spatial frequencies reduces image noise,

thereby improving contrast resolution while at the same time reducing spatial resolution.

Lastly, iterative reconstruction techniques result in multislice helical CT images with

higher contrast resolution compared to the use of filtered back projection reconstruction

methods (19). Relative to multislice helical CT, cone beam CT images demonstrate poor

contrast resolution due to a high amount of scatter radiation and subsequent image noise

associated with cone beam geometry, as well as due to inherent flat panel deficiencies

that result in a non-linear response to incoming x ray photons (1).

1.3.2 Spatial Resolution

Spatial resolution is defined as the ability of an imaging system to record separate

structures that are positioned closely together; that is, it reflects the level of detail seen on

an image (19). Several factors influence spatial resolution in both multislice helical and

cone beam CT.

1.3.2.1 CT Image Geometry

CT techniques require a long object-to-detector distance, which results in significant

magnification of the object being imaged. This geometrical principle, in combination

8

with focal spot blooming associated with the use of high current techniques and x ray

beam divergence, all contribute to a reduction in CT spatial resolution by ultimately

increasing the focal spot size.

1.3.2.2 Nyquist Limitation and Sampling Frequency

Digital imaging techniques, including helical multislice and cone beam CT, define object

size in terms of spatial frequency, expressed graphically as a sine wave. Smaller objects

correspond to a higher spatial frequency. The Nyquist frequency, or limitation, refers to

the spatial frequency of a particular object. For a small, high frequency object to be

accurately imaged, the sampling frequency (i.e., the rate of data “measurement”) must be

at least twice that of the object’s Nyquist limit. This sampling frequency is a determinant

of the limiting spatial resolution of a given imaging system, which defines the smallest

object that is reliably depicted on the final image.

1.3.2.3 Detector Element Size

A smaller detector volume element (“voxel”) size results in increased spatial resolution

as a result of reduced partial volume averaging effects. This applies to both multislice

helical and cone beam CT. While voxel length and width (x- and y-dimensions) in

multislice helical CT are equivalent and determined by the picture element (“pixel”) size

of the detector, the voxel height is generally greater and determined by the acquired slice

thickness in the axial (z) dimension. Typical multislice helical CT pixel sizes are 0.5 mm

for a 25 cm diameter field-of-view, and the acquired slice thickness ranges from

approximately 0.5mm up to 5mm (24). Cone beam CT utilizes a flat panel detector to

acquire circumferential two-dimensional planar images around the area of interest. There

is no inherent acquired “slice thickness” of cone beam CT; rather, cross sectional images

are reconstructed from the two-dimensional projection data, and the displayed voxel size

is a direct product of the native pixel dimensions. This technique results in isotropic

voxels (i.e., equal dimension in x-, y-, and z-planes), and permits multiplanar

reconstruction of the images without loss of spatial resolution. Voxel sizes in cone beam

9

CT imaging range from 0.076mm to 0.4mm, depending on the particular unit and

protocol being used.

1.3.2.4 Image Reconstruction Filter

A reconstruction filter applied to the CT images is used to balance image noise (i.e.,

contrast resolution) and spatial resolution, depending on the imaging task at hand.

Sharpening or edge enhancement filters increase spatial resolution at the expense of

increased image noise, which is a useful application for visualization of hard tissue

structures. Smoothing filters conversely reduce image noise while reducing spatial

resolution, and are applied when soft tissue structures are of interest. While multislice

helical CT images offer both bone and soft tissue algorithms by utilization of these

differing reconstruction filters, only bone algorithms are useful and applicable to cone

beam CT images (19).

1.3.3 Prior Research on Spatial Resolution and Diagnostic Efficacy

Voxel size is a known determinant of image spatial resolution. The ability to detect

subtle hard tissue findings on CT imaging requires use of a sufficiently small voxel size

such that partial volume effects do not obscure the findings of interest. Librizzi et al.

(25) evaluated the effect of voxel size on the ability to detect cortical erosions of the

temporomandibular joints using dry human skulls. Their protocol used the Hitachi CB

MercuRay cone beam unit operating at 120kVp and 15mA. Modulation of voxel size

with this system requires a companion change in the field-of-view; the

0.2mm/0.3mm/0.4mm voxel sizes correspond to the 6-inch/9-inch/12-inch field-of-view

settings, respectively. A clear advantage of using dry human skulls is the ability to elicit

information regarding the sensitivity, specificity, and receiver operator characteristic

(ROC) curve. The data from this study demonstrated that images acquired using the 6-

inch field-of-view with 0.2mm voxel size provided a significant diagnostic advantage

compared to those attained using the 12-inch field-of-view and 0.4mm voxel size. It is

important to note that the change in field-of-view produces a concurrent change in the

10

amount of scatter radiation, which affects image signal-to-noise ratio and contrast

resolution, and therefore overall image quality.

Other dental disciplines such as endodontics have evaluated the influence of voxel size

on the diagnostic ability of cone beam CT. Liedke et al. (26) assessed the effect of voxel

size on evaluation of simulated external root resorption, using an i-CAT cone beam CT

unit. The field-of-view was held constant at 8cm, and the voxel sizes evaluated were

0.2mm, 0.3mm, and 0.4mm. No significant differences in sensitivity, specificity,

positive predictive value, or negative predictive value were demonstrated between the

three different voxel sizes. However, the likelihood ratios indicated that the 0.2mm and

0.3mm voxel sizes permitted an easier diagnosis of external root resorption compared to

the 0.4mm voxel size.

1.4 Diagnostic Imaging of the Temporomandibular Joint

1.4.1 Patient Selection Criteria

A position paper by the American Academy of Oral and Maxillofacial Radiology

(AAOMR) recommends the use of selection criteria to establish the need for

temporomandibular joint imaging (27). Acquisition of a thorough patient history and

clinical examination is required to determine if the use of imaging tools will impact the

patient’s diagnosis and/or treatment and that the benefit of radiation exposure outweighs

the potential risks. When considering the dose imparted upon a patient by diagnostic

imaging procedures utilized in Oral and Maxillofacial Radiology, the stochastic risk of

carcinogenesis is of primary concern. The most conservative, linear no-threshold model

implies that while the risk of stochastic events is low, it is not zero, thus prudent selection

criteria must be exercised to avoid unnecessary radiation exposure.

1.4.2 Goals

The goals of temporomandibular joint imaging are defined by the AAOMR as follows: 1)

to evaluate the integrity of the structures when disease is suspected, 2) to confirm the

11

extent of known disease, 3) to stage the progression of known disease, or 4) to evaluate

the effects of treatment. The AAOMR also states, “If there is a choice between imaging

modalities that are expected to equally influence the management of the patient, the least

expensive, in terms of cost and radiation dose, should be selected.” (27) This statement

is congruent with the radiation protection principle of optimization, which indicates that

the total exposure remains as low as reasonably achievable (“ALARA”), with economic

and social factors taken into account (13). Selection of appropriate views with

collimation to the area of interest, optimized technique factors (including voltage,

current, and exposure time), and use of leaded aprons and thyroid collars, all act as

effective dose reduction protocols that minimize patient exposure.

1.4.3 Choice of Imaging Modality

The choice of imaging tool for assessment of the temporomandibular joint is dependent

on the diagnostic question. Direct visual examination is considered the gold standard for

assessment (11), however this poses obvious impracticality in living subjects. Computed

tomography (CT) or cone beam CT are considered first line imaging modalities for

visualization of the hard tissue structures of the joint, thus are well suited for diagnosis of

osseous abnormalities including arthridities, neoplasia, and trauma (28,29,30,31). The

use of magnetic resonance (MR) imaging provides excellent depiction of the soft tissue

joint components, and is considered the diagnostic tool of choice for assessment of

abnormalities of articular disc position, disc perforation, and joint effusion. While MR

imaging does allow evaluation of the osseous structures, hard tissue image quality is

inferior to that of CT (10). Additional factors such as cost of the procedure,

invasiveness, radiation dose, potential side effects, and impact of information gained

from imaging the patient must also be considered.

12

1.5 Degenerative Joint Disease

1.5.1 Pathophysiology

One of the most common pathological conditions involving the hard tissue structures of

the temporomandibular joints is degenerative joint disease, also referred to as

osteoarthritis. Degenerative joint disease is characterized as a non-inflammatory

arthritis, in which mechanical intra-articular stresses overwhelm intrinsic joint repair and

remodeling mechanisms. This ultimately results in a loss of equipoise between the

formation and degradation of the articular cartilage and underlying subchondral bone,

which leads to aberrations in normal joint anatomy (1,32,33). While the pathophysiology

of degenerative joint disease is complex, it is generally accepted that the primary insult is

mechanical in nature, followed by a subsequent release of inflammatory mediators and

free radicals that propagate the disease process (34,35).

1.5.2 Structural Changes

The manifestations of osteoarthritis are usually observed as a combination of

degenerative and proliferative components. The articular fibrocartilage of the

temporomandibular joint undergoes softening, fibrillation, ulceration, and loss, with

subsequent exposure of the underlying cortical bone (36). This process is followed by

the appearance of cortical erosions along the articulating surfaces. Formation of

subchondral bone cysts (Ely cysts) may also occur. Proliferative effects are a

compensatory effort by the joint components to meet increased functional demands, and

include structural changes such as subchondral sclerosis and osteophyte formation (32).

Though the presence of articular surface flattening is often denoted as a feature of

degenerative joint disease, this may simply represent adaptive joint remodeling that

serves to increase the articulating surface area over which forces are distributed (1).

13

1.5.3 Diagnostic Imaging

Based on an underlying pathophysiology that involves the hard tissues of the joint, the

structural changes of degenerative joint disease are best visualized using a technique that

optimally depicts the osseous joint components. The Research Diagnostic Criteria for

Temporomandibular Disorders (RDC/TMD) Validation Project concluded that multislice

helical computed tomography (CT) is a superior modality to either panoramic

radiography or magnetic resonance (MR) imaging for assessment of temporomandibular

joint osteoarthritis (7). Prior studies have shown that the use of cone beam CT

demonstrates no significant difference in detection of osseous abnormalities within the

temporomandibular joint compared to multislice helical CT (9,37). Cone beam CT

affords the advantage of a reduced radiation dose burden, and therefore should be

considered the modality of choice for assessing hard tissue structures of the

temporomandibular joints for changes related to degenerative joint disease (8).

Information acquired from these diagnostic imaging procedures may help assist and

direct patient management. Patient education, lifestyle modifications, limitation of

parafunctional habits, and pharmacotherapy may all potentially play a role in limiting the

progression and burden of degenerative joint disease. Furthermore, imaging allows the

clinician to rule out other more ominous disease processes that may mimic

temporomandibular joint dysfunction.

14

1.6 Statement of the Problem

1.6.1 Comparative Dosimetry

As radiologists, we have a responsibility to follow the principle of ALARA (“as low as

reasonably achievable”) when exposing patients to ionizing radiation. Although

effective radiation doses involved in diagnostic radiography are exceedingly low

compared to those used to develop dose-response curves related to observable biological

effects, ALARA requires the acceptance of the most conservative, linear no-threshold

model. This implies that no dose is deemed entirely safe, and thus it is prudent to ensure

patient exposure is minimized while still providing diagnostic quality images. While

cone beam CT offers a reduced radiation dose compared to multislice helical CT, there is

a wide range of effective doses rendered by commercially available cone beam CT

systems. Though the standard protocol for temporomandibular joint imaging at the

author’s institution offers simultaneous bilateral scanning of the right and left joints, the

resulting field-of-view encompasses a far greater volume than the desired area of interest.

Honda et al. (38) published a paper outlining the use of “ortho cubic super-high

resolution computed tomography” for temporomandibular joint imaging by an adapted

Scanora cone beam CT unit. This technique provided a field-of-view restricted to the

circumferential volume surrounding the temporomandibular joint, measuring 38mm in

diameter by 32mm in height, with a voxel size of 0.136mm. However, no effective

radiation dose values were provided by this study to permit comparison to larger field

techniques.

Previous dosimetry studies measuring effective radiation dose for various cone beam CT

systems during maxillofacial imaging procedures indicate a significantly greater dose for

the large field-of-view Hitachi CB MercuRay compared to the limited field-of-view

Kodak 9000 3D unit (8,21). However, no study has directly assessed the effective

radiation dose imparted when the field-of-view is centered about the temporomandibular

joints. Depending on which anatomical structures lie within the irradiated tissue volume,

effective radiation dose will change accordingly. The comparative dosimetry for

15

standard large field-of-view cone beam CT temporomandibular joint imaging compared

to a limited field-of-view technique has not been previously explored.

1.6.2 Image Quality

Not only does the Kodak 9000 3D cone beam CT unit offer the potential for a reduction

in radiation dose to the patient, it also features a smaller voxel size (0.076mm versus

0.20/0.29/0.40mm) and thus improved spatial resolution compared to the Hitachi CB

MercuRay. Spatial resolution has a significant impact on the amount of image detail

appreciated by an observer, and in turn is a critical component of diagnostic efficacy. To

date, studies investigating comparative image quality of various computed tomographic

techniques have largely revolved around multislice helical CT versus cone beam CT.

Only one published study by Librizzi et al. (25) compared the effect of field-of-view and

voxel size on diagnostic efficacy and effective dose when using cone beam CT to detect

erosions of the temporomandibular joint. However, this in vitro study was done using

artificially created erosions in dry human skulls, and compared voxel sizes ranging from

0.2mm to 0.4mm with concurrently varying field-of-view from 6-inches to 12-inches.

Increasing the field-of-view results in increased scatter radiation and decreased image

contrast resolution, thereby creating a confounding factor when evaluating diagnostic

efficacy of the varying image voxel size. No study to date has evaluated the use of

isolated voxel size variation on the ability to detect in vivo osseous changes within the

temporomandibular joints.

16

1.7 Aim

The first aim of this research was to establish comparative dosimetry values for the

effective radiation dose from various cone beam CT examinations of the

temporomandibular joints. In addition to the traditional technique of utilizing a single

large field-of-view acquisition to simultaneously image the right and left joints, an

alternative limited field-of-view technique was also explored to determine the effect of

reducing both the irradiated field size and operating technique factors on the effective

radiation dose values.

The clinical component of this study was designed to assess the effect of cone beam CT

voxel size on the ability to detect osseous changes associated with degenerative joint

disease of the temporomandibular joint. Software manipulation permitted synthetic

transformation of acquired native image data into a larger voxel size, thereby creating a

forum for comparison of the effect of spatial resolution on diagnostic efficacy. Cone

beam CT examinations at two different voxel sizes were also evaluated to determine if

modifying spatial resolution is related to a difference in perceived image quality by

observers.

17

1.8 Objectives

1. To calculate and compare the effective radiation dose values for

temporomandibular joint imaging procedures using two different cone beam CT

systems, each operating under differing technique factors and field-of-view parameters.

2. To determine the effect of modulating cone beam CT technique factors on

effective radiation dose.

3. To evaluate the effect of voxel size on diagnostic efficacy in detecting osseous

changes in the temporomandibular joint associated with degenerative joint disease.

4. To determine the effect of voxel size on perceived cone beam CT image quality.

18

1.9 Hypotheses

1.9.1 Primary hypotheses

1. The cone beam CT unit used during temporomandibular joint imaging has an

effect on the calculated effective radiation dose. Increased exposure and field-of-view

parameters will increase the effective dose.

2. Both voltage (kVp) and current (mA) are directly related to the effective radiation

dose (i.e., increasing one or both of these technique factors will result in an increase in

calculated effective radiation dose).

3. Cone beam CT image voxel size is inversely related to the ability to detect

osseous changes observed in degenerative joint disease of the temporomandibular joint

(i.e., smaller voxel size improves diagnostic efficacy of osseous changes).

4. Images with smaller voxel size (higher spatial resolution) will be designated as

higher image quality compared to those images with larger voxel size (lower spatial

resolution).

1.9.2 Null hypotheses

1. The cone beam CT unit used for temporomandibular joint imaging has no effect

on effective radiation dose, regardless of exposure and field-of-view parameters.

2. Modulating cone beam CT technique factors of voltage (kVp) and current (mA)

has no effect on calculated effective radiation dose.

3. Alteration of voxel size of acquired cone beam CT images has no effect on the

ability to detect osseous changes in the temporomandibular joint.

4. Image voxel size has no effect on perceived image quality by observers.

19

Chapter 2

2 Materials and Methods

2.1 Part A: Comparative Dosimetry

2.1.1 Overview

At the author’s institution, the standard protocol for imaging of the osseous structures of

the temporomandibular joint is the use of a Hitachi CB MercuRay cone beam CT unit

(Hitachi Medical Systems, Tokyo, Japan), using a spherical 9-inch (22.9cm) field-of-

view, and operating at 100 kilovoltage potential (kVp), 10 milliamperes (mA), and 9.6

seconds (s) of total exposure time. This technique permits simultaneous, bilateral

imaging of both temporomandibular joints within a single cone beam CT volume.

This study evaluates the use of a limited field-of-view cone beam CT imaging technique

to perform separate acquisitions of the right and left temporomandibular joints. The

Kodak 9000 3D cone beam CT system (Carestream Dental, Rochester, NY, USA) offers

a limited field-of-view cylindrical imaging volume, measuring 5cm in diameter and

3.7cm in height. Standard adult technique factors operate at 70kVp and 10mA, with a

total exposure time of 10.8s.

Although previous data suggest that effective radiation doses imparted by the Kodak

9000 3D cone beam CT unit (5.3µSv to 38.3µSv) (21) are significantly lower than those

of the Hitachi CB MercuRay (407µSv to 1073µSv) (8), these measurements were not

performed with the field-of-view centered about the temporomandibular joints. Thus,

this comparative dosimetry study evaluates the effective radiation dose rendered during

temporomandibular joint imaging using the a single, 9-inch field-of-view Hitachi CB

MercuRay acquisition versus successive right and left joint scans using the Kodak 9000

3D unit.

A supplementary comparative dosimetry study was designed to evaluate the effect of

varying technique factors using the Kodak 9000 3D cone beam CT unit for

20

temporomandibular joint imaging. In addition to the standard adult setting of 70kVp and

10mA used in the initial part of this study, the unit offers three additional preset kVp/mA

combinations optimized for variable patient sizes: child 68kVp/6.3mA, youth/small adult

70kVp/8mA, and large adult 74kVp/10mA. These exposure settings were applied to the

same protocol for bilateral limited field-of-view temporomandibular joint imaging as

described in the following sections.

2.1.2 Materials for Dosimetric Measurements

An anthropomorphic RANDO® man phantom (Alderson Research Laboratories,

Stanford, CT, USA) comprised of a human skeleton embedded in isocyanate rubber

provided an experimental model to acquire dosimetric measurements. The isocyanate

rubber is equivalent to human soft tissues in both density and atomic number, and thus

provides a comparable radiation attenuation profile (39). The phantom is sectioned into

2.5cm thick axial slices; the first ten were used in this study, extending from the vertex of

the head to the level of the clavicles (Figure 1). Twenty-five optically stimulated

luminescence (OSL) dosimeters (InLight® nanoDot™, Landauer, IL, USA) placed in

various locations throughout the head and neck region of the anthropomorphic phantom

(Table 1) were used to measure absorbed radiation doses for both cone beam CT units

(Figure 2). Dosimeter sites of placement were selected to represent radiosensitive organs

and regions relevant to dental imaging, following the methods described by Ludlow et al.

(40). The OSL dosimeters are comprised of aluminum oxide scintillator crystals, which

produce and trap light when exposed to ionizing radiation. The standard unscreened

nanoDot™ used in this study has a reported lower limit of detection of 10µSv and

accuracy of ±5% (Appendix 1). To calibrate for background radiation exposure,

unexposed control dosimeters were submitted along with the experimental dosimeters for

analysis by Landauer.

2.1.3 Imaging Techniques

The RANDO® man phantom was positioned in the Hitachi CB MercuRay unit with the

occlusal plane parallel to the floor, the mid-sagittal plane centered medio-laterally in the

21

imaging field, and the condylar head level centered supero-inferiorly within the volume.

A single cone beam CT acquisition was performed using the panoramic mode (“P-

mode”, 9-inch field-of-view) setting, with technique factors of 100kVp, 10mA, and 9.6s.

Measurements were performed in triplicate for this protocol.

Positioning of the RANDO® man phantom in the Kodak 9000 3D cone beam CT unit

required greater exactness to ensure that both the temporal and condylar components of

the temporomandibular joint were completely imaged and centered within the volume.

Bilateral indicator guides affixed to the surface of the anthropomorphic phantom were

aligned with the temporal supports to maintain consistency in vertical and horizontal

positioning between successive acquisitions. The image sensor was first oriented parallel

to the anatomical mid-sagittal plane to align the rotational center of the cone beam unit

with the temporomandibular joint region of interest. Antero-posterior localization was

determined by positioning the laser indicator light approximately 1cm anterior to the

external auditory meatus landmark. The supero-inferior position was defined by

centering the midpoint of the 3.7cm vertical field-of-view light over a point

corresponding to the level of the condylar head in the closed mouth position. Finally, the

medio-lateral position was set using the Kodak 9000 3D Module software, placing the

crosshair immediately medial to the condylar head of interest (right or left). These

alignment parameters produced a dataset with the RANDO® man condylar head

omnidirectionally centered within the imaging volume. The Kodak 9000 3D acquisitions

were attained using technique factors of 70kVp, 10mA, and a 10.8s scan time, and both

unilateral and bilateral measurements were acquired. Three successive scans were

performed on each set of OSL dosimeters to ensure absorbed dose quantities exceeded

the lower limit of detection, and each series was performed at minimum in triplicate.

The evaluation of varying technique factors was performed using an identical protocol to

that described above for the Kodak 9000 3D unit, but with appropriate exposure setting

modifications for the three different patient sizes. Technique factors were manually

modified rather than selecting the preset patient size hotkeys to retain patient positioning

parameters as described above. Only bilateral temporomandibular joint measurements

were acquired during this component of the study.

22

2.1.4 Dosimetry Calculations

Single scan measured absorbed doses (AD, provided in millirads, mrad) for each

dosimeter were first converted into SI units (microgray, µGy) by the following formula:

AD (µGy) = AD (mrad) * (10µGy/1mrad)

The converted absorbed dose data (µGy) were then transformed into equivalent doses

(EQD, microsieverts, µSv) using the following equation:

EQD (µSv) = AD (µGy) * wR

where wR is the radiation weighting factor for the particular type and energy of radiation

involved (for diagnostic x rays, wR = 1).

The following formula was applied to determine effective doses for each tissue type, T

(EFDT, µSv):

EFDT (µSv) = !(EQDn / n * wT * fT)

where wT is the tissue weighting factor for tissue type T, and fT is the fraction of tissue

type T irradiated within the field-of-view. Tissue weighting factors were based on the

2007 International Commission on Radiological Protection (ICRP) recommendations

(41). Values applied for the fraction of tissue irradiated followed those suggested by

Ludlow et al. (40), which were originally estimated for full field-of-view craniofacial

imaging. Table 2 outlines details of parameters used for calculation of the effective

tissue doses, including the 2007 ICRP tissue weighting factors (wT), estimated fraction of

tissue irradiated (fT), and OSL dosimeter identification numbers corresponding to the

particular tissue types.

Finally, all weighted effective tissue doses were summated to provide a total effective

dose (EFDtotal, µSv) for each imaging modality using the following equation:

EFDtotal (µSv) = !(EFDT1 + EFDT2 + … + EFDTn)

23

2.1.5 Statistical Analyses

Mean total effective doses for each of the imaging techniques were established based on

the triplicate scan data, and are expressed as mean effective dose (µSv) ± standard

deviation (µSv). The difference in effective dose between groups was determined by

one-way analysis of variance (ANOVA) and Tukey post-hoc statistical tests. All

statistical analyses were performed using SPSS version 17.0 software (SPSS Inc,

Chicago, IL, USA). Data were deemed statistically significantly different when p<0.05. !

24

Figure 1. Left lateral view of the anthropomorphic RANDO® man phantom.

25

Figure 2. Sample OSL dosimeter placement at level 4 of the anthropomorphic

RANDO® man phantom to measure absorbed dose for the lens and orbit of the right and

left eye.

26

Table 1. Anatomical correlates of OSL dosimeters in RANDO® man anthropomorphic

phantom, as described by Ludlow et al. (40).

Phantom

Level Anatomical Location OSL ID number

Anterior calvarium 1 Midbrain 2 Posterior calvarium 3

2

Left calvarium 4 3 Pituitary fossa 5

Right lens 6 Right orbit 7 Left lens 8

4

Left orbit 9 5 Right cheek 10

Right parotid gland 11 Right ramus 12 Left parotid gland 13 Left ramus 14

6

Cervical spine 15 Right mandibular body 16 Right submandibular gland 17 Right sublingual gland 18 Left sublingual gland 19 Left mandibular body 20 Left submandibular gland 21

7

Left back of neck 22 Right thyroid surface 23 Thyroid midline 24 9 Pharynx 25

!!!!!!!

27

Table 2. Effective tissue dose calculation factors.

Tissue/Organ Tissue weighting factor, wT

a

Estimated fraction

irradiated, fTb

OSL ID number(s)

Bone marrow 16.5% Mandible 1.3% 12, 14, 16, 20 Calvarium 11.8% 1, 3, 4 Cervical spine

0.12

3.4% 15 Thyroid 0.04 100% 23, 24 Esophagus 0.04 10% 25 Skin 0.01 5% 6, 8, 10, 22 Bone surface 16.5%

Mandible 1.3% 12, 14, 16, 20 Calvarium 11.8% 1, 3, 4 Cervical spine

0.01

3.4% 15 Salivary glands 100%

Parotid 100% 11, 13 Submandibular 100% 17, 21 Sublingual

0.01

100% 18, 19 Remainder

Lymphatic nodes 5% 11-21, 24, 25 Muscle 5% 11-21, 24, 25 Extrathoracic airway 100% 7, 9, 11-21, 24, 25 Oral mucosa

0.009 eachc

100% 11-14, 16-21 a Based on 2007 International Commission on Radiological Protection (ICRP) recommendations (41). b Based on recommended values by Ludlow et al. (40). c Remainder tissue/organs tissue weighting factor 0.12 total, divided by 13 possible tissues/organs.

!!!!!!

28

2.2 Part B: Voxel Size and Diagnostic Efficacy

2.2.1 Overview

The Hitachi CB MercuRay 9-inch field-of-view temporomandibular joint imaging

protocol provides reconstructed images with a 0.29mm isotropic voxel size, whereas the

voxel size of reconstructed images acquired by the Kodak 9000 3D unit is 0.076mm

(76µm). A known inverse relationship between voxel size and spatial resolution

indicates that the Kodak 9000 3D images are of higher spatial resolution compared to

those rendered by the Hitachi CB MercuRay.

Since the ability to visualize small changes within the osseous structures is dependent on

the amount of image detail and sharpness, it is reasonable to theorize that images with

higher spatial resolution may provide a diagnostic advantage.

The clinical component of this study was designed to determine the effect of voxel size

on diagnostic efficacy of osseous changes within the temporomandibular joints related to

degenerative joint disease. By utilizing a software-mediated downsampling technique,

the voxel size of Kodak 9000 3D images can be altered, thereby permitting the

comparison of differing spatial resolutions applied to a single cone beam CT acquisition.

2.2.2 Ethics Approval

The Health Sciences Research Ethics Board of the University of Toronto granted ethics

approval for the clinical component of this study, following the completion of

comparative dosimetry analysis (Appendix 2). Patient identifiers were kept confidential

and were removed from the data and thesis.

2.2.3 Equipment Modifications Required for Clinical Use

To translate the technique previously described for imaging the temporomandibular

joints using the Kodak 9000 3D cone beam CT unit from an inanimate anthropomorphic

phantom to living human subjects, two modifications were required.

29

2.2.3.1 Modified Chin Support

A plastic molded chin rest provided by Kodak was used to aid patient positioning and

stabilization during cone beam CT acquisition. Though this chin support adequately

maintained vertical patient positioning, it did not provide a means to adjust the antero-

posterior parameter. To overcome this obstacle, a Hoffman open jaw compressor clamp

(Avogadro’s Lab Supply Inc., Miller Place, NY, USA) was used to provide an anterior

stop for the chin rest position (Figure 3). This clamp could be easily adjusted to meet the

unique antero-posterior positioning requirements for each individual patient.

2.2.3.2 Estimation of Subject Intercondylar Distance

Antero-posterior and supero-inferior positioning using the indicator light was equally

effective and predictable for either the anthropomorphic phantom or a living subject.

However, the medio-lateral positioning is determined strictly by the Kodak software

module crosshairs rather than by a physical landmark projected on the particular subject

being imaged. Determination of the idealized position of the Kodak software module

crosshairs for RANDO® man was found to be located just medial to the medial pole of

the condylar head of interest. A caliper was created to estimate the intercondylar

distance for RANDO® man based on the measured distance between the right and left

preauricular areas (Figure 4). This was found to be approximately 13cm.

To determine the optimized crosshair position for various estimated intercondylar

distances, the facial midline was marked and the anthropomorphic phantom was

manipulated through a series of controlled and measured lateral shifts. For example, by

shifting the midline mark by 1cm to the right and imaging only the right

temporomandibular joint, this simulated an intercondylar distance of 15cm, while

shifting the midline mark by 1cm to the left and imaging the right temporomandibular

joint represented an intercondylar distance of 11cm. This provided a means to better

predict medio-lateral crosshair positioning requirements for living human subjects, in

which a range of intercondylar distances naturally exists (Figure 5).

30

2.2.4 Study Design

A prospective crossover design was used for the clinical component of this study.

Twenty-two subjects with suspected degenerative joint disease presenting to the Oral and

Maxillofacial Radiology clinic at the University of Toronto, Faculty of Dentistry for

temporomandibular joint imaging were recruited for this study. Patient information and

consent forms are provided in Appendix 3. Intercondylar distance was estimated using

the caliper tool, which assisted medio-lateral positioning of the software module

crosshairs. All subjects were imaged with the Kodak 9000 3D cone beam CT unit, using

the bilateral temporomandibular joint acquisition technique with the modifications

previously described, resulting in a total of 44 joints imaged. Operating technique

factors were 70kVp, 10mA, and 10.8s, and all images were acquired at the native voxel

size of 76µm. Figure 6 illustrates correct subject positioning within the Kodak 9000 3D

cone beam CT unit for temporomandibular joint imaging.

2.2.4.1 Inclusion Criteria

Informed consent-capable patients presenting with signs and/or symptoms of

degenerative joint disease of the temporomandibular joints were included in the study.

These clinical features include the following: 1) crepitus on opening/closing; 2) pain on

mandibular movement; 3) limited mandibular opening (may be associated with joint

pain); 4) lateral palpation of the condyle causing increased patient pain and/or

discomfort; and 5) loading of the joint causing increased patient pain and/or discomfort.

2.2.4.2 Exclusion Criteria

Exclusion criteria were applied to those subjects presenting with signs and/or symptoms

of isolated soft tissue abnormalities of the temporomandibular joints (i.e., disc

displacement without clinical evidence of associated degenerative joint disease), cases of

acute trauma to the craniofacial structures, and pregnant female subjects.

31

2.2.5 Image Processing and Downsampling

Acquired images were saved in two formats using the CS 3D Dental Imaging software

(Carestream Dental, Rochester, NY, USA): 1) at a default 76µm (0.076 mm) voxel size

(high resolution), and 2) at a downsampled 300µm (0.300 mm) voxel size (low

resolution). This provided a total of 88 temporomandibular joint cone beam CT volumes

for review.

Downsampling merges the data from several adjacent voxels into a single larger voxel.

This results in a reduction of spatial resolution due to increasing the voxel size, but also

reduces image noise thereby improving contrast resolution. The CS 3D Dental Imaging

software provides downsampling options of 100µm, 200µm, 300µm, 400µm, 500µm, and

1mm. The choice to use 300µm downsampled images provided a theoretical simulation

of the spatial resolution of the Hitachi CB MercuRay system conventionally used at our

institution for temporomandibular joint imaging, which has a native voxel size of

0.29mm. The downsampling procedure provided a realistic and practical comparison

between high and low spatial resolution cone beam CT images, and precluded the need

for duplicate scanning of each subject. Figure 7 provides an illustration of the effect of

the downsampling technique on a representative temporomandibular joint Kodak 9000

3D cone beam CT volume.

2.2.6 Image Analysis

Each image volume was anonymized, blindly coded, and randomized by an individual

not acting as an observer in the study. Three observers (all nationally certified Oral and

Maxillofacial Radiologists) independently reviewed the images of the

temporomandibular joints using the CS 3D Dental Imaging software. Prior to review of

the study sample cases, the three observers underwent a calibration exercise to improve

interobserver reliability (Appendix 4). After a washout period of two weeks, one of the

observers reviewed a subset of the series (22 volumes, 25% of the total study sample) a

second time to determine intraobserver reliability. Observers were free to manipulate the

data in any plane of view, to modulate image brightness and contrast, and to use the

32

zoom function as desired. To facilitate and expedite case analyses, observers were

permitted to utilize a computer and monitor of their choice, and no restrictions regarding

ambient viewing conditions were imposed. No time limit was imparted upon the

observers to reach an interpretation for each case. Agreement on the presence or absence

of a feature between two of the three examiners was interpreted as truth. There was no

attempt made to resolve disagreement between observers.

The following features of degenerative joint disease involving the condylar or temporal

component of the joint were noted for each case as a dichotomous variable (yes if the

feature is present, no if the feature is absent): 1) cortical erosion; 2) subchondral

sclerosis; 3) flattening; 4) osteophyte or joint mouse/mice; and 5) Ely (subchondral) cyst.

In addition to evaluation for the presence of specific radiographic features, a visual

analog scale was provided for each volume. Observers were asked to place a single hash

mark along a 10cm line that represented their perceived image quality, ranging from low

image quality on the left to high image quality on the right.

A sample score sheet for identification of radiographic features and the visual analog

scale is depicted in Appendix 5.

2.2.7 Statistical Analyses

Interobserver reliability was evaluated using Fleiss’ kappa using an Excel-based program

designed for multirater data, as the SPSS software does not provide an algorithm for

comparing more than two observers (42,43). All remaining data analysis was carried out

using SPSS version 17.0 software (SPSS Inc, Chicago, IL, USA). Cohen’s kappa was

used to determine intraobserver reliability. Kappa values of agreeability were defined

according to the criteria defined by Landis and Koch (44). The McNemar’s chi-squared

test for paired groups evaluated the effect of voxel size on detection of osseous changes

related to degenerative joint disease for each of the aforementioned categories of

radiographic findings. All cases demonstrated a small number of discordant pairs (<25),

thus the SPSS software automatically used the binomial distribution to provide a two-

sided significance value, rather than using the conventional chi-squared distribution.

33

Finally, the paired samples t-test was used to measure the effect of changing voxel size

on visual analog scale ratings by the observers. Data were considered significant when

p<0.05.

34

Figure 3. Modified chin support with the Hoffman open jaw compressor clamp attached

to modulate subject antero-posterior positioning in the Kodak 9000 3D cone beam CT

unit during a temporomandibular joint imaging procedure.

35

Figure 4. Caliper tool for estimation of intercondylar distance.

!

36

Figure 5. Kodak acquisition module software medio-lateral crosshair positioning guide

based on estimated intercondylar distance.

37

Figure 6. Correct subject positioning within the Kodak 9000 3D cone beam CT unit for

temporomandibular joint imaging.

38

Figure 7. Downsampling technique applied to a temporomandibular joint image volume

acquired using the Kodak 9000 3D cone beam CT system. (A) and (B) represent

corrected coronal and sagittal images, respectively, at the native 76µm voxel size.

Images (C) and (D) represent corrected coronal and sagittal images, respectively, at a

downsampled 300µm voxel size.

A B

C D

39

Chapter 3

3 Results

3.1 Part A: Comparative Dosimetry

Table 3 outlines the mean effective tissue doses and the summated total mean effective

doses for the various cone beam CT imaging modalities and technique factors

investigated during the comparative dosimetry study. The mean effective radiation dose

for the Hitachi CB MercuRay technique was 223.6±1.1µSv, compared to 9.7±0.1µSv and

20.5±1.3µSv for the unilateral and bilateral Kodak 9000 3D acquisitions, respectively,

when operating at the standard adult (70kVp, 10mA) setting. Modifying the Kodak

technique factors resulted in mean effective doses of 9.7±0.1µSv (68kVp, 6.3mA),

13.5±0.5µSv (70kVp, 8mA), and 19.7±0.6µSv (74kVp, 10mA) for the child, youth, and

large adult settings, respectively.

The difference in mean effective dose between groups was significant at p<0.0001,

determined by one-way ANOVA. Tukey post-hoc analysis showed that all bilateral

acquisition groups significantly differed from one another (p<0.05), with the exception of

the Kodak standard adult and large adult settings (p=0.652).

40

Table 3. Mean effective tissue doses and total effective doses with respective standard

deviation values for each of the temporomandibular joint imaging modalities and

technique settings.

Mean Effective Tissue Dose (µSv)

Imaging Modality/Technique Setting

Bilateral Kodak

Hitachi

Unilateral Kodak Child Youth Standard

Adult Large Adult

Tissue/Organ

100kVp 10mA

70kVp 10mA

68kVp 6.3mA

70kVp 8mA

70kVp 10mA

74kVp 10mA

Bone marrow 58.23 1.72 1.54 2.17 3.28 3.21

Thyroid 18.90 0.94 0.51 0.93 1.87 1.51

Esophagus 1.99 0.11 0.06 0.12 0.22 0.14

Skin 2.25 0.36 0.40 0.49 0.49 0.61

Bone surface 4.87 0.14 0.13 0.18 0.27 0.27

Salivary glands 36.73 1.85 1.67 2.31 3.84 3.32

Brain 30.32 0.86 1.58 2.18 2.42 3.13

Lymphatic nodes 1.51 0.08 0.07 0.10 0.16 0.14

Muscle 1.51 0.08 0.07 0.10 0.16 0.14

Extrathoracic airway 32.00 1.71 2.06 2.75 4.09 4.08

Rem

aind

er

Oral mucosa 35.29 1.88 1.60 2.22 3.72 3.18

Mean effective dose (µSv) 223.6 9.7 9.7 13.5 20.5 19.7

Standard deviation (µSv) 1.1 0.1 0.1 0.5 1.3 0.6

41

3.2 Part B: Voxel Size and Diagnostic Efficacy

Tables 4 and 5 depict interobserver and intraobserver reliability data, respectively, for

detection of osseous changes related to degenerative joint disease. Interobserver

reliability for all radiographic features combined yielded kappa coefficients of 0.31 and

0.30 for the 76µm and 300µm voxel sizes, respectively. This denotes “fair” strength of

interobserver agreement overall, according to the Landis and Koch criteria.

Intraobserver reliability kappa coefficient for all radiographic features combined was

0.69, which indicates “substantial” strength of agreement.

Table 6 outlines the effect of voxel size on detection of osseous changes related to

degenerative joint disease as determined by the McNemar "2 test for paired groups.

Based on majority data (considered to be when at least two of the three observers agree

on the presence or absence of an osseous finding), there was no significant difference in

feature detection when comparing the 76µm and 300µm voxel sizes. Even when each

observer’s responses were considered individually, only a single observer found condylar

flattening to differ significantly (p<0.05) between the two different voxel sizes.

The mean visual analog scale (VAS) response by observers for the 76µm images was 7.4,

compared to 7.1 for the 300µm voxel size. This difference was statistically significant

(p=0.020) as determined by the paired samples t-test (Table 7). All observers tended to

rate the 76µm images with slightly higher perceived image quality (Figure 8).

42

Table 4. Fleiss’ kappa for interobserver reliability.

VOXEL SIZE

76µm 300µm RADIOGRAPHIC FEATURE Number (n) of

positive agreementsa kappa Number (n) of

positive agreementsa kappa

Cortical erosion 10 0.21 15 0.14

Subchondral sclerosis 18 0.11 18 0.19

Flattening 19 0.26 17 0.03

Osteophyte/joint mouse 9 0.56 6 0.19 CO

ND

YL

AR

C

OM

PON

EN

T

Subchondral (Ely) cyst 5 0.55 6 0.68

Cortical erosion 7 -0.07 5 0.03

Subchondral sclerosis 13 0.22 6 0.16

Flattening 9 0.20 11 0.32

Osteophyte/joint mouse 1 0.40 3 0.33 TE

MPO

RA

L

CO

MPO

NE

NT

Subchondral (Ely) cyst 0 -0.01 0 -0.01

All radiographic features combined 91/440 (20.7%) 0.31 87/440 (19.8%) 0.30

a Number (n) of positive agreements (i.e., at least two out of three observers denoted the feature as “present”) out of a possible of 44 for each radiographic feature category. For all radiographic features combined, the number of positive agreements represents a summation of the column total.

43

Table 5. Cohen’s kappa for intraobserver reliability.

Number (n) of positive findingsa RADIOGRAPHIC FEATURE

First Observation Second Observation

kappa

Cortical erosion 6 7 0.46

Subchondral sclerosis 13 14 0.52

Flattening 18 18 0.70

Osteophyte/joint mouse 6 7 0.46 CO

ND

YL

AR

C

OM

PON

EN

T

Subchondral (Ely) cyst 3 5 0.70

Cortical erosion 0 1 n/ab

Subchondral sclerosis 4 6 0.49

Flattening 9 9 0.62

Osteophyte/joint mouse 0 0 n/ab TE

MPO

RA

L

CO

MPO

NE

NT

Subchondral (Ely) cyst 0 0 n/ab

All radiographic features combined 59/220 (26.8%) 67/220 (30.5%) 0.69

a Number (n) of positive findings out of a possible of 22 for each radiographic feature category. For all radiographic features combined, the number of positive findings represents a summation of the column total. b No kappa coefficient can be calculated if the first and/or second categorical observations demonstrated no significant findings (all responses = 0).

44

Table 6. Radiographic feature identification results based on the McNemar "2 test for

paired groups.

Two-sided p-value (exact significance)a RADIOGRAPHIC FEATURE

Majority Observer 1 Observer 2 Observer 3

Cortical erosion 0.180 1.000 1.000 0.344

Subchondral sclerosis 1.000 1.000 0.065 0.774

Flattening 0.727 1.000 0.375 0.021

Osteophyte/joint mouse 0.250 0.500 0.500 0.289 CO

ND

YL

AR

C

OM

PON

EN

T

Subchondral (Ely) cyst 1.000 1.000 0.500 1.000

Cortical erosion 0.687 1.000 0.210 0.625

Subchondral sclerosis 0.092 0.687 0.581 0.581

Flattening 0.687 1.000 1.000 0.508

Osteophyte/joint mouse 0.500 0.500 1.000 n/ab TE

MPO

RA

L

CO

MPO

NE

NT

Subchondral (Ely) cyst n/ab n/ab 1.000 n/ab

a All cases demonstrated a small number of discordant pairs (<25), thus the binomial distribution was used to provide a two-sided significance value, rather than using the conventional chi-squared distribution. b No p-value can be calculated if the first and/or second categorical observations (76µm or 300µm) demonstrated no significant findings (all responses = 0).

45

Table 7. Effect of voxel size on visual analog scale (VAS) responses by observers based

on a paired samples t-test.

Voxel Size Mean VAS Rating

n (number of paired observations) t-statistic dfa Significance (two-

sided p-value)

76µm 7.4 132

300µm 7.1 132 2.351 131 0.020

a Degrees of freedom, which is determined by the number of paired observations minus 1 (df = n – 1).

46

Figure 8. Visual analog scale ratings of image quality for the overall average from all

observers, as well as from each observer independently, for the 76µm and 300µm voxel

sizes.

47

Chapter 4

4 Discussion

4.1 Part A: Comparative Dosimetry

4.1.1 Hitachi CB MercuRay Versus Kodak 9000 3D

The dosimetry data demonstrate that utilization of separate right and left

temporomandibular joint limited field-of-view cone beam CT acquisitions provides more

than a ten-fold reduction in effective radiation dose compared to the larger single field

acquisition for a standard adult patient (223.6µSv for the Hitachi CB MercuRay 9-inch

field-of-view acquisition versus 20.5µSv for two limited field-of-view Kodak 9000 3D

acquisitions). Because the estimated fractions of tissues irradiated were based on 12-inch

field-of-view cone beam CT estimates, which includes the active bone marrow of the

entire cranium, mandible, and most of the cervical vertebrae, the thyroid gland, and all

major salivary glands, our results for the Kodak 9000 3D acquisition may be an

overestimation of the percentage of tissue irradiated within the limited field-of-view

temporomandibular joint imaging volume. Therefore, the dose reduction provided by the

Kodak 9000 3D might be, in reality. even greater than indicated by our calculations. The

effective radiation dose of the bilateral Kodak 9000 3D acquisitions is comparable to that

imparted by most digital panoramic radiographic systems, which has been reported to

range between 14.7µSv to 24.5µSv (45). In addition to generating high quality three-

dimensional images of the temporomandibular joints, the limited field-of-view imaging

protocol may offer dental practitioners equipped with only a limited field-of-view cone

beam CT unit an opportunity to provide temporomandibular joint imaging for their

patients at a radiation dose comparable to a typical panoramic radiograph.

Previous dosimetry data indicate a significant difference in effective radiation dose

between the Hitachi CB MercuRay and Kodak 9000 3D cone beam CT systems, but did

not specifically measure radiation dose when the field-of-view is centered about the

temporomandibular joints. Ludlow and Ivanovic investigated comparative dosimetry of

48

64-slice medical CT and eight different cone beam CT units, including the Hitachi CB

MercuRay, using a similar technique to our study protocol (8). Cone beam CT devices

were compared using varying field-of-view sizes, and International Commission on

Radiological Protection (ICRP) tissue weighting factors were based on the 2007

guidelines. The 6-inch, 9-inch, and 12-inch field-of-view effective doses for the Hitachi

CB MercuRay operating at “maximum quality” settings of 120kVp and 15mA were

407µSv, 560µSv, and 1073µSv, respectively. The Hitachi CB MercuRay produced the

highest effective dose of all the cone beam units when considering the 9-inch field-of-

view; only the 64-slice Somaton multidetector medical CT dose was greater (860µSv).

The 12-inch field-of-view effective dose for the Hitachi CB MercuRay was also

evaluated using “standard quality” settings of 100kVp and 10mA, and this rendered an

effective radiation dose of 569µSv, which represents about a 47% reduction in dose

compared to when the “maximum quality” technique factors were used. If the effective

dose for a 9-inch field-of-view acquisition of 560µSv while operating at 120kVp and

15mA from the Ludlow and Ivanovic study is scaled by the same 47% reduction in dose

when using 100kVp and 10mA settings, this would theoretically yield an effective dose

of approximately 297µSv. The present study demonstrated an effective dose of

223.6µSv for a 9-inch field-of-view Hitachi CB MercuRay temporomandibular joint

study, which is in reasonable agreement with this hypothetical value based on the

aforementioned study.

Jadu et al. evaluated effective radiation doses for cone beam CT sialography, centering

either the parotid or submandibular gland within the image field (46). The study

compared effective doses for the 6-inch, 9-inch, and 12-inch field-of-view options for the

Hitachi CB MercuRay, operating at variety of kVp and mA settings. When the parotid

gland was centered within the image field, the respective effective doses for the 6-inch,

9-inch, and 12-inch fields-of-view were 97µSv, 275µSv, and 466µSv with 100kVp and

10mA exposure settings. Centering the submandibular gland generated effective doses

of 261µSv, 275µSv, and 466µSv, respectively. The increased effective dose during

submandibular gland imaging using a 6-inch field-of-view was explained by increased

exposure of the radiosensitive thyroid gland. These data also demonstrate good

agreement with the present study; as expected, centering the temporomandibular joints

49

within the field-of-view imparts less radiation dose upon radiosensitive structures such as

the thyroid, submandibular, and sublingual glands, which explains why the measured

effective radiation dose in this study is less than that found by Jadu et al.

In comparison to the large field-of-view cone beam CT imaging modalities, little work

has been published on the effective dose from limited field systems. Ludlow compared

effective radiation doses for the anterior and posterior regions of the maxilla and

mandible using the Kodak 9000 3D unit, operating at 70kVp and 10mA (21). Effective

doses ranged from 5.3µSv for the anterior maxilla to 38.3µSv for the posterior mandible.

Conceivably, the posterior maxilla would most closely represent the temporomandibular

joint region of interest in the present study. The effective radiation dose for this area was

found by Ludlow to be 9.8µSv, which is in good agreement with our 9.7µSv result for a

unilateral temporomandibular joint Kodak 9000 3D acquisition.

Based on earlier dosimetry studies, it is clear that there is large variation in the effective

radiation dose imparted by various cone beam CT systems. The comparative dosimetry

study by Ludlow and Ivanovic (8) demonstrated a range in effective dose from 69µSv

rendered by the Classic i-CAT standard scan compared to 560µSv for the Hitachi CB

MercuRay operating in the panoramic mode (9-inch field-of-view), with both machines

utilizing an equivalent field-of-view technique. Technical factors used in the study for

the two devices vary considerably; the Hitachi CB MercuRay utilizes a scan time of 10s,

operating at 120kVp and 15mA, whereas the Classic i-CAT standard settings operate at

120kVp and 5mA over a 20s acquisition time. Clearly, when using the Kodak 9000 3D

for bilateral temporomandibular joint acquisitions, the dose reduction is more significant

when comparing the values to the Hitachi unit versus the i-CAT system. However, this

Kodak temporomandibular joint imaging technique does still provide approximately a

three- to four-fold dose reduction compared to that from the relatively low dose classic i-

CAT standard scan.

It should be noted that this study used optically stimulated luminescence (OSL)

dosimeters, whereas the aforementioned studies utilized thermoluminescent dosimeters.

The decision to use OSL dosimeters was predicated on their enhanced sensitivity to low

50

dose radiation compared to the thermoluminescent dosimeters, with a purported lower

limit of detection of 10µGy (Appendix 1). While dose readouts for thermoluminescent

dosimeters require heating and result in destruction of the dosimeter, OSL dosimeter

readout is achieved by use of stimulation with 540nm light photons and can be repeated

if required (47). An ideal dosimeter is equally sensitive to radiation exposure in all

directions, such that orientation of the dosimeter has no bearing on the amount of

radiation absorbed. In this study, the orientation of the OSL dosimeters was consistent

between scan repetitions, with the flat 1x1cm surface of the dosimeters oriented parallel

to the incoming x ray beam. Reproducibility in dosimeter orientation is necessary to

ensure that absorbed dose data are fairly compared and contrasted between different

acquisitions. Variability in dosimeter orientation between studies creates a potential

confounding factor for data comparison. A study comparing measured radiation doses

by thermoluminescent and OSL dosimeters found a strong correlation between the two

systems (r2=0.99), which suggests that comparison between data produced by the two

dosimeters is feasible (48). This experiment also demonstrated significant angular

dependence of both the thermoluminescent and OSL dosimeters, but no significant

difference in the magnitude of angular dependence between the two systems was

observed. This finding implies that consistency in dosimeter orientation is indeed of

paramount importance to validate comparisons between absorbed dose data within an

investigation, but also creates uncertainty in the ability to reliably evaluate data between

different studies.

Another potential limitation in interpretation of the existing comparative dosimetry

research involves reported variability in dosimeter-derived measurements based on the

number of dosimeters used to obtain absorbed dose values. For example, the studies by

Ludlow (21) and Pauwels et al. (49) both evaluated dosimetry for the Kodak 9000 3D

cone beam CT unit in the anterior maxilla using the 2007 International Commission on

Radiological Protection (ICRP) tissue weighting factors, with reported effective doses of

5.3µSv and 19µSv, respectively. Whereas Ludlow placed thermoluminescent dosimeters

at 24 sites throughout an adult skull phantom, Pauwels et al. used approximately 150

dosimeters. The use of a greater number of thermoluminescent dosimeters is believed to

increase measurement accuracy since the absorbed dose for a particular organ is

51

calculated as a mean of all absorbed doses measured by the dosimeters placed within that

specific area of interest. More dosimeters reduce the variability in measured dose

resulting from a slight change in position of the primary beam, and also improve

reproducibility of dosimetric data. Because optically stimulated luminescence (OSL)

dosimeters are significantly larger than thermoluminescent dosimeters (3mm x 3mm x

1mm), there are obvious limitations to the number of dosimeters that could be placed

without structural compromise and an alteration in the attenuation profile characteristics

of the anthropomorphic phantom.

4.1.2 Translating Exposure to Risk

Dosimetry studies often provide an annual background radiation effective dose

equivalency to the measured radiation dose imparted by a particular radiographic

examination (8,45). Based on the most recent data published for the United States

population, the annual background radiation dose is approximately 3.1mSv (3100µSv)

per person (50), which equates to about 8.5µSv each day. While there is a tendency to

directly compare the dose burden rendered by a diagnostic imaging procedure to

“equivalent days of background radiation”, caution must be exercised in interpreting

these data in this way. Background radiation delivers a chronic, whole body exposure,

and often involves high-energy gamma rays or particulate radiation, whereas diagnostic

imaging results in an acute exposure applied to a limited anatomical region and generally

utilizes lower energy x ray photons. Taking these disclaimers into account, the

background equivalency for a temporomandibular joint examination by the Hitachi CB

MercuRay is approximately 26.3 days, compared to about 2.4 days for the bilateral

standard adult Kodak 9000 3D technique (Appendix 6). This comparison is likely most

useful as an aid to provide inquisitive patients with a concept of the relative amounts of

radiation they are exposed to during an imaging procedure.

A further extrapolation of comparative dosimetry research is to estimate excess

population risk, which again makes several important assumptions including a normal

population distribution regarding both age and gender. A risk coefficient of 0.055 events

per sievert (41,45) is the commonly accepted value for carcinogenesis risk determination.

52

In our study, the Hitachi CB MercuRay temporomandibular joint examination would thus

result in a probability of 12 cases of fatal cancer per one million exposures, versus 1.1

cases in one million bilateral standard adult Kodak 9000 3D exposures (Appendix 6).

Similar to comparing effective radiation dose to background radiation, this provides a

tool for explaining the risk of a procedure to a patient in the simple and easily

understandable terms of “x in a million”.

4.1.3 Kodak 9000 3D Technique Factor Modulation

Modulation of the voltage and current exposure factors on the Kodak 9000 3D results in

a significant reduction in effective radiation dose when the child (9.7µSv) and

youth/small adult (13.5µSv) settings were used compared to the standard adult settings

(20.5µSv). Radiosensitivity is inversely related to age; young patients are approximately

ten times more sensitive to the deleterious effects of ionizing radiation compared to

adults (12). This observation is consistent with the Law of Bergonie and Tribondeau

(51), which states that radiosensitivity is greatest for cells with a high mitotic rate, with

many potential future divisions, and that are undifferentiated. While these

generalizations were initially applied to the cellular level, extrapolation of this data to a

young individual undergoing active growth and development is only logical. As a result,

the use of prudent selection criteria and dose reduction techniques is imperative in

younger patient populations. This becomes particularly important in cases where

multiple radiographic examinations are required to monitor disease progression. Juvenile

idiopathic arthritis involves the temporomandibular joints in approximately 40% of cases

(1), and the potentially progressive nature of the disease often necessitates serial imaging

studies. The use of a bilateral limited field-of-view cone beam CT temporomandibular

joint examination for these patients using the youth/small adult technique factor settings

yields a 34% lower dose than the standard adult protocol, and provides superior images

of the osseous joint structures compared to magnetic resonance (MR) imaging.

It is important to note that while minimizing radiation dose is important, this cannot be

done at the expense of diagnostic image quality. X ray beam current (mA) is

proportional to the signal-to-noise ratio of an image. Increasing the mA setting by a

53

factor of two concurrently increases the signal-to-noise ratio by a factor of !2, or 1.41

(19). This implies that the use of the child (6.3mA) and youth (8mA) exposure settings

would result in a signal-to-noise ratio of 0.79 and 0.89 that of the standard adult

technique, respectively. If this results in image quality that is no longer diagnostic, the

advantage of a reduction in effective radiation dose is nullified. The inclusion of the

high-density temporal bone in the imaging volume also must be considered, as extensive

beam attenuation in this region may further contribute to deteriorated image quality

under low current conditions. Analysis of image quality using these varying technique

factors in child- and youth-sized anthropomorphic phantom should be performed before

routine implementation of such dose reduction protocols can be recommended.

No significant difference was noted between the standard adult and large adult

techniques (20.5µSv versus 19.6µSv, p=0.652). These two techniques varied only in

voltage setting (70kVp for standard adult versus 74kVp for large adult), with the current

held constant at 10mA. An increase in potential kilovoltage results in a more energetic x

ray beam and a greater number of x ray photons; that is, it increases both beam quality

and quantity. Higher energy photons have a reduced chance of being absorbed and

contributing to dose (19). Thus, while the net number of x ray photons is increased by

increasing the kVp setting, the actual number of photons absorbed is also decreased,

which may provide an explanation why the standard adult and large adult effective

radiation dose values did not demonstrate a significant difference.

A potential limitation of this study component arises from the use of a single

anthropomorphic phantom intended to simulate an average sized adult male subject. The

author’s institution did not have access to a child, youth/small adult, or large adult

phantom, thus all of the experiments involving modulation of technique factors were

performed using the standard adult male equivalency. As a phantom increases in size,

there is a greater volume of tissue between the surface and center of the phantom, and the

absorbed radiation dose at the center is roughly half that measured at the surface (52).

Conversely, a smaller phantom resembling a pediatric subject would demonstrate more

uniform surface and central doses due to less peripheral attenuation of the x ray beam.

This equates to a higher absorbed dose in a smaller subject, and ultimately a higher

54

calculated effective dose (53). However, head diameter varies relatively little between

pediatric and adult subjects, relative to other anatomical sites such as the abdomen (54).

When comparing a standard and large sized adult, the difference in head diameter is

likely to be of even less clinical significance. Thus, the use of a 16cm phantom for head

CT scans is generally considered acceptable for the purpose of calculating comparative

dosimetry values in all age groups (55). While our effective radiation dose data for the

child and youth technique factor settings would likely be marginally increased if the

respective sized phantoms were utilized, our current protocol is still deemed acceptable

and valid within the present dosimetry research and body of knowledge.

4.1.4 Future Directions in Comparative Dosimetry Research

Though most dental comparative dosimetry studies to date utilize dosimeters placed

within an anthropomorphic phantom, issues such as variability in dosimeter positioning

relative to the incoming x ray beam and the use of a limited number of dosimeters to

estimate total doses to organs or tissues result in methodological weakness. A recent

publication outlined the use of an alternative technique known as the Monte Carlo dose

computation to measure dosimetry for the next generation i-CAT cone beam CT unit

(56). Monte Carlo analyses use computer-based simulations to estimate both primary

and scattered photon interactions within a standardized International Commission on

Radiological Protection (ICRP) computational phantom (57), and purportedly mitigates

many of the shortcomings of dosimeter-based techniques (19,56). Using the 16cm

diameter by 13cm height field-of-view for dentoalveolar imaging, the Monte Carlo

effective dose was calculated at 66µSv (56), compared to a value of 83µSv published by

Pauwels et al. (49) using approximately 150 thermoluminescent dosimeters for the same

cone beam CT acquisition. As more researchers adopt the Monte Carlo technique for

comparative dosimetry analyses, there will likely be some modest revisions to the

presently accepted effective radiation dose values for various oral and maxillofacial cone

beam CT imaging protocols.

55

4.2 Part B: Voxel Size and Diagnostic Efficacy

4.2.1 Effect of Voxel Size on Detection of Osseous Changes

The clinical component of this study evaluated the effect of Kodak 9000 3D cone beam

CT image voxel size on the ability to detect osseous changes related to degenerative joint

disease, in which each case acted as its own control. While it was hypothesized that

osseous changes would be better appreciated when viewing images with a smaller voxel

size (i.e., higher spatial resolution), this was not in fact found to be the case. No

significant difference between the native 76µm voxel size and the downsampled 300µm

voxel size was detected for any of the degenerative joint disease related changes when

observer data were compiled. Even when each observer was considered on an individual

basis, only one individual rated a difference in visualization of condylar component

flattening between the two different voxel sizes. One would expect that subtle changes

such as small cortical erosions would be more readily observed at a higher spatial

resolution, whereas detection of more grossly evident changes such as flattening and

subchondral sclerosis would be less dependent on voxel size. Unfortunately, because

observers were not required to quantify the size of cortical erosions, statistical analyses

of these data are not possible. It is important to note that while no significant difference

was noted between the two groups, this finding can only be applied to Oral and

Maxillofacial Radiologists and cannot be reliably extrapolated to other dental

practitioners. Further analysis is required to determine if differences in training and

experience play a role in the detection of osseous changes under varying spatial

resolution parameters.

Interobserver agreement for both the 76µm and 300µm voxel sizes was found to be only

“fair”, with respective kappa coefficients of 0.31 and 0.30. The low frequency of some

of the radiographic features may have contributed to these relatively low interobserver

agreement values (Table 5), and ultimately this may have weakened the statistical

analysis when evaluating the effect of voxel size on detection of osseous changes. A

possible improvement in the study design would include attempted resolution of observer

disagreement to reach a true consensus on radiographic feature identification, rather than

56

the majority approach utilized in the current analysis. Furthermore, observers were given

a forced decision matrix model when evaluating the temporomandibular joints for

osseous changes related to degenerative joint disease. There was no opportunity for

observers to indicate a level of confidence in their designation of the presence or absence

of a particular radiographic feature. While obvious osseous changes would be

considered by most as an objective finding and show little interobserver variability, more

subtle changes likely demonstrate greater subjectivity and depend on each observer’s

unique threshold for diagnosis. The inclusion of a visual analog scale for observers to

rank their confidence level would provide an additional dimension for data analysis.

Additionally, increasing the number of cases evaluated would increase study power and

reduce the likelihood of a type II statistical error, in which a false null hypothesis is not

rejected.

The finding that voxel size does not impact the ability to detect osseous changes cannot

be extrapolated beyond the Kodak 9000 3D to other cone beam CT imaging systems,

including the Hitachi CB MercuRay. While downsampling Kodak 9000 3D data to

300µm theoretically provides a spatial resolution similar to the native Hitachi CB

MercuRay panoramic mode 0.29mm voxel size, the resulting images differ

conspicuously (Figure 9). Diversity in the type of sensor and field-of-view both

contribute to variability in image quality, which is primarily determined by the

parameters of spatial resolution and contrast resolution. The Hitachi CB MercuRay uses

an image intensifier sensor united with a charge coupled device (CCD) camera, while the

Kodak 9000 3D uses a complementary metal oxide sensor (CMOS). Factors such as

thickness and atomic number of the detector material and the speed of the sensor all

contribute to the final spatial resolution and contrast resolution of an imaging system.

The next contributory factor to image quality difference between the two cone beam CT

systems involves the field-of-view, which is much larger for the Hitachi CB MercuRay

compared to the Kodak 9000 3D (9-inch/22.9cm sphere versus 5cm diameter by 3.7cm

high, respectively). By increasing the field-of-view, there is a concordant increase in the

amount of scatter radiation. This results in more image noise (i.e., a decreased signal-to-

noise ratio) and ultimately reduces image contrast resolution. Field-of-view modulation

has no impact on spatial resolution. One advantage of this study design is the ability to

57

isolate the test variable, voxel size, while maintaining consistency in all other variables

through the manipulation of a single cone beam CT acquisition into two different

viewing parameters. This eliminated potential confounding factors from the data

analysis, thereby permitting stronger and more focused study conclusions.

4.2.2 Effect of Voxel Size on Perceived Image Quality

While images with a smaller voxel size conferred no diagnostic advantage, observers

denoted the higher spatial resolution cone beam CT datasets to be of superior image

quality. Downsampling the data from 76µm to 300µm reduced the spatial resolution, but

increased the contrast resolution through improvement of the signal-to-noise ratio. This

suggests that Oral and Maxillofacial Radiologists find spatial resolution a more important

parameter than contrast resolution when evaluating image quality. An objective

evaluation of the effect of downsampling on contrast resolution through calculation of

the signal-to-noise and contrast-to-noise ratios is a potential area of further research.

4.2.3 Study Limitations

While this is the first clinical study to describe the use of the Kodak 9000 3D cone beam

CT system for temporomandibular joint imaging and to compare the effect of spatial

resolution on diagnostic efficacy of osseous changes within the temporomandibular

joints, the use of living patients as subjects renders specific limitations. While it would

have been more realistic to directly compare the ability to detect osseous changes when

using the conventional Hitachi CB MercuRay unit versus the alternative Kodak 900 3D

cone beam CT system, this is not consistent with ethical radiology practice or the

principles of radiation protection. The downsampling technique thus provided an

alternative means to simulate cone beam CT data at two different voxel sizes without the

need to perform multiple acquisitions. The use of living human subjects also precluded

comparison of imaging findings with the gold standard for detection of osseous changes

related to degenerative joint disease, which is direct visualization performed through

autopsy studies or the use of dry skull specimens. As a result, it was not possible to

evaluate the number of true and false radiographic findings, both positive and negative,

58

reported by observers in this study. This limits the calculation of sensitivity, specificity,

accuracy, and receiver operating characteristic (ROC) curve data.

59

Figure 9. Native Hitachi CB MercuRay panoramic mode 0.290mm temporomandibular

joint images compared to 300µm downsampled Kodak 9000 3D images using the

anthropomorphic phantom. (A) and (B) represent corrected coronal and sagittal images,

respectively, for the Hitachi CB MercuRay. Images (C) and (D) represent corrected

coronal and sagittal images, respectively, for the Kodak 9000 3D at a downsampled

300µm voxel size.

B

A

C

D

60

4.2.4 Drawbacks of Limited Field-of-View Imaging

The Kodak 9000 3D cone beam CT system offers an excellent alternative to conventional

large field-of-view temporomandibular joint imaging. However, the clinical component

of this study highlighted a few specific challenges associated with this novel protocol.

Centering the joint within the image volume is technique sensitive and requires a

significant time investment compared to positioning a patient for a large field-of-view

study. Medio-lateral positioning was by far the most unpredictable parameter, even with

use of the caliper and indicator guide. Variability in subject soft tissue profiles likely

explains this issue. Problems with supero-inferior positioning were most often noted

when the condylar head was difficult to palpate upon mandibular opening, thus

complicating the supero-inferior landmarking step. Such errors were generally confined

to incomplete imaging of the temporal component of the joint, specifically cropping off

the roof of the glenoid fossa. Antero-posterior localization was the most predictable

parameter, probably because an easily identifiable anatomical landmark (1cm anterior to

the external auditory meatus) was used as a reference.

Although there were a small number of re-acquisitions required because of these

positioning difficulties, modifying the inaccurate parameter provided resolution in the

follow-up scan with a high degree of certainty. Even with an additional acquisition using

the Kodak 9000 3D unit, the total effective radiation dose is still vastly less than what

would be rendered by the Hitachi CB MercuRay system.

4.2.5 Practical Considerations

Based on the aforementioned voxel size data, one may initially conclude that it is still

desirable to use the higher spatial resolution images since the perceived image quality is

greater, despite conferring no diagnostic advantage. However, the storage footprint and

portability of cone beam CT data should also be taken into account. A typical bilateral

Kodak 9000 3D temporomandibular joint study acquired at a 76µm voxel size requires

about 404 megabytes (MB) of computer data storage. Downsampling the same study to

100µm or 200µm reduces this requirement to 186MB (54% reduction) or 26MB (94%

61

reduction), respectively. When the data are downsampled to the 300µm voxel size used

in this study, which demonstrated no difference in diagnostic efficacy compared to the

native 76µm voxel size, the storage requirement is reduced to 8MB, a 98% reduction.

Not only does this produce a significant reduction in the storage footprint, but it also

allows for enhanced file transferability via e-mail communication. While one of the

advantages of digital imaging is greater portability of information between practitioners,

this becomes limiting when large file sizes must be transferred. The downsampling

module creates a quick and simple solution to this problem.

The practical economic implications of this study must also be addressed. Limited field-

of-view cone beam CT units are significantly less expensive than the larger field-of-view

systems. Many clinicians are averse to the limited field scanners based on the notion that

imaging is confined to the dentoalveolar regions. This research outlines a

straightforward technique to expand the conventional capabilities of a limited field-of-

view cone beam CT system, providing high quality images the temporomandibular

joints. Furthermore, the restricted irradiated volume of tissue results in a significantly

reduced radiation dose, which must always be an implicit part of the decision making

process when prescribing a radiographic examination.

62

Chapter 5

5 Conclusions

This is the first study to evaluate comparative dosimetry specific to temporomandibular

joint cone beam CT imaging. The use of bilateral limited field-of-view Kodak 9000 3D

cone beam CT acquisitions of the temporomandibular joints provides more than a ten-

fold reduction in the effective radiation dose compared to the Hitachi CB MercuRay

technique traditionally used at our institution. Modulation of the Kodak 9000 3D cone

beam CT system exposure factors provides a further opportunity to reduce radiation

dose, particularly to younger, more radiosensitive patients.

While the Kodak 9000 3D cone beam system offers the smallest voxel size of any

commercially available cone beam CT unit at 76µm, there was no significant difference

in the detection of osseous changes related to degenerative joint disease by Oral and

Maxillofacial Radiologists when comparing the native high spatial resolution images to

those with a downsampled voxel size of 300µm. Despite no effect on diagnostic

efficacy, perceived image quality was consistently higher for images with greater spatial

resolution.

The use of a limited field-of-view cone beam CT temporomandibular joint imaging

protocol offers a viable alternative to conventional larger field-of-view techniques, and

should be considered a first line tool for imaging the osseous component of the

temporomandibular joint.

63

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Appendix 1 Landauer Specification Sheet for

72

73

Appendix 2

Health Sciences Research Ethics Board Approval Letter

74

Appendix 3

Patient Information and Consent Forms Title of Research Project Development of a limited field-of-view cone beam CT imaging technique for evaluation of the temporomandibular joints (TMJs) Investigator(s)

1. Principal Investigator Dr. Trish Lukat DDS

M.Sc. candidate Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 647-985-8165

2. Faculty Supervisor Dr. Ernest Lam DMD, PhD, FRCD(C)

Associate Professor Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 416-979-4932 x4385

Purpose of the Research

The purpose of this study is to evaluate the diagnostic performance of a high-resolution limited field-of-view cone beam CT scan of the temporomandibular joints (TMJs) with respect to detection of bony changes related to degenerative joint disease (also kn

75

Description of the Research Subject population

Adult patients referred to the Special Procedures Clinic in the Discipline of Oral and Maxillofacial Radiology at the Faculty of Dentistry, University of Toronto for evaluation of the osseous structures (bones) of the temporomandibular joint(s). Inclusion criteria

Informed consent-capable individuals with a suspected degenerative joint disease condition associated with one or both of the temporomandibular joint(s) as determined by clinical examination of the patient. See Appendix A for details. Exclusion criteria

Individuals excluded from this study include: subjects with clinical signs and symptoms of isolated soft tissue abnormalities of the temporomandibular joint (e.g. disk displacement without clinical evidence of associated degenerative joint disease); cases of acute trauma to the craniofacial structures, in which comprehensive rather than localized imaging is indicated; and pregnant subjects. Background information

The current protocol for temporomandibular joint cbCT imaging at our institution utilizes a Hitachi CB MercuRay unit, with a 9-inch field-of-view and 100kVp and 10mA exposure settings. This technique permits simultaneous bilateral scanning of the right and left temporomandibular joints, generates images with a voxel size of 0.290mm, and exposes the patient to an effective radiation dose of 223.6 1.1 Sv.

The present study utilizes an alternative high-resolution/reduced radiation dose temporomandibular joint imaging technique using a Kodak 9000 3D unit to perform separate limited field-of-view cbCT scans of the right and left TMJs. This modality has a field-of-view of 5.0cm diameter by 3.75cm in height and uses 70kVp and 10mA exposure settings. The patient will be scanned twice, one scan for each joint; this exposes the patient to a total effective radiation dose of 20.5 1.3 Sv, which offers more than a 10-fold reduction in dose compared to using the present standard of care protocol described above. Due to a smaller voxel size within the Kodak sensor (0.076mm), the resultant images are also of comparatively higher spatial resolution compared to those generated using the Hitachi CB MercuRay. Temporomandibular joint cone beam CT procedure

A thorough explanation of the cone beam CT procedure will be given to each patient prior to consenting to the examination. Upon approval, a Resident in Oral and Maxillofacial Radiology at the Faculty of Dentistry, University of Toronto, will perform the cone beam CT procedure. The Principal Investigator or a faculty member will closely supervise the Resident. Temporomandibular joint cone beam CT imaging procedures are routinely performed in the Special

76

Procedure clinic, and the supervising faculty members are experienced in the performance of this procedure. As part of the comprehensive radiographic assessment, a panoramic radiograph will be taken prior to cone beam CT imaging to assess for abnormalities or pathology located outside the joints.

Positioning of the patient within the Kodak 9000 3D unit requires precision to ensure that both the condylar and temporal components are completely imaged. A chin rest and temporal supports are used to stabilize the patient in the appropriate position, and this permits imaging of the temporomandibular joints in the closed mouth position. With the occlusal plane parallel to the floor and the patient in maximum intercuspation, the antero-posterior position is first determined by positioning the indicator light approximately 1cm anterior to the external auditory meatus landmark. The supero-inferior position is then determined by centering the midpoint of the 3.75cm vertical field-of-view light over a point corresponding to the level of the condylar head in the closed mouth position. Finally, the medio-lateral position is set using the Kodak 9000 3D Module software, based on patient intercondylar distance estimated by caliper measurement. The procedure will be repeated for the contralateral joint; the patient position will not require modification, only the crosshairs will be adjusted within the software prior to imaging the second joint.

The results of the temporomandibular joint examination will be reported to the patient at the completion of the examination. As well, a digital copy of the radiographic images that were obtained for the patient will be couriered to the referring dentist or physician accompanied by a radiographic report stating the findings of the examination.

Image analysis

The cbCT images for each joint of each patient will be anonymized and reviewed using (1) the default, high-resolution 0.076mm voxel size, and (2) a voxel downsampling technique where the resultant voxel size will be rendered at 0.300mm. The downsampling technique will be performed using the Carestream CS 3D Dental Imaging Software, and will provide images of reduced spatial resolution. This will permit a comparison of images viewed under two differing conditions (high versus low spatial resolution), while sparing the patient from being exposed to two different imaging modalities. Three observers, all nationally certified Oral and Maxillofacial Radiologists, will review the cbCT images for each patient independently. As the images are digitally acquired, they will be reviewed at computer workstations where the observers will have the advantage of enhancing the images by manipulating brightness and contrast. The reviewing radiologists will be blinded to the clinical data and will be required to fill out a form similar to that displayed in Appendix B for each image series. The presence or absence of a particular radiographic feature will be based on agreement of at least two of the three observers, and there will be no attempt to reconcile disagreements. As well, one of the observers will review a portion of the series twice so that intraobserver reliability may be determined.

77

Potential Harm, Injuries, Discomforts or Inconvenience Cone beam CT imaging of the temporomandibular joint is non-invasive,

and carries negligible risk. A strict aseptic technique is always followed during the procedure as a standard of practice. Possible drawbacks of the alternative Kodak imaging protocol compared to the standard Hitachi protocol include longer scan times to acquire images of each joint individually and a greater precision requirement with respect to patient positioning due to a smaller field-of-view. However, the trade off of a lower radiation dose to the patient deems this a viable alternative, despite the potential disadvantages.

With respect to radiation doses, we have recently completed a dosimetric study comparing the effective radiation doses using the Hitachi CB MercuRay and the Kodak 9000 3D to image the temporomandibular joints. An anthropomorphic phantom with optically stimulated luminescence (OSL) dosimeters placed in 25 locations throughout the head and neck region of the phantom was subjected to the two imaging modalities. The Hitachi CB MercuRay was operated using a 9-inch field-of-view, 100kVp, and 10mA; the Kodak 9000 3D technique was performed individually for each joint using the default 5cm diameter by 3.75cm height field-of-view, and operating at 70kVp and 10mA. The results were presented at the 2011 meeting of the American Academy of Oral and Maxillofacial Radiology in Chicago, IL. Our results found that the effective doses for the Hitachi CB Mercuray temporomandibular joint acquisition were 223.6 1.1 Sv, compared to 20.5 1.3 Sv for the bilateral Kodak 9000 3D modality. Effective radiation dose for a unilateral joint acquisition using the Kodak 9000 3D is 9.7 0.1 Sv. Potential Benefits

By agreeing to participate in this study, patients undergoing cbCT imaging of the temporomandibular joint will benefit from this dose-reduction technique to acquire three-dimensional images of their joints. We hypothesize that the superior spatial resolution of the Kodak 9000 3D unit will provide more detailed diagnostic information than the current technique using the lower-resolution Hitachi CB MercuRay unit. We believe that the additional information obtained by this technique will allow for more accurate quantification of osseous changes within the temporomandibular joint related to degenerative joint disease, thereby aiding the treating physician or dentist in choosing the most appropriate management option for the patient and improve the quality of patient care. Alternatives

If you elect at any time not to participate in this study, the current temporomandibular joint imaging protocol using the Hitachi CB MercuRay unit will be offered. Confidentiality

Confidentiality will be respected and no information that discloses the identity of the subject will be released or published without consent unless

78

required by law. Patient data will be anonymized with the identities of the patients known only to the Principal Investigator.

Participation Participation in research is voluntary. If you choose to participate in this

study you can withdraw at any time. Should you choose to withdraw, your data will be removed from the database. There will be no consequences with respect to your future care in the Faculty. Contact If you have any questions about this study, please contact:

Dr. Trish Lukat DDS

M.Sc. candidate Division of Oral and Maxillofacial Radiology Faculty of Dentistry, University of Toronto 124 Edward Street, Division of Oral and Maxillofacial Radiology Toronto, ON M5G 1G6 647-985-8165 trish.lukat@utoronto.ca

If you have any complaints or concerns about how you have been treated as a research participant, please contact:

Zaid Gabriel Research Ethics Officer, Health Sciences Zaid.gabriel@utoronto.ca or 416-946-5806

79

Appendix A. Clinical examination criteria for signs/symptoms of degenerative joint disease associated with the temporomandibular joint(s). History Patient describes unilateral or bilateral joint pain that is aggravated by mandibular movement. Pain is usually constant; may worsen in the late afternoon or evening. Patient may describe parafunctional habits.

Clinical Characteristics Limited mandibular opening may be noted as a result of joint pain. Crepitus on opening/closing. Pain on mandibular movement. Lateral palpation of the condyle may increase patient pain/discomfort. Loading of the joint may increase patient pain/discomfort.

80

Appendix B. Sample score sheet for observers to record presence of radiographic features of degenerative joint disease. If the feature noted in the column is present, place a check mark ( ) in the respective box. CONDYLAR COMPONENT TEMPORAL COMPONENT

CASE ID

corti

cal e

rosi

ons

subc

hond

ral

scle

rosi

s

flatte

ning

oste

ophy

te o

r jo

int m

ouse

/mic

e

Ely

(sub

chon

dral

) cy

st

corti

cal e

rosi

ons

subc

hond

ral

scle

rosi

s

flatte

ning

oste

ophy

te o

r jo

int m

ouse

/mic

e

Ely

(sub

chon

dral

) cy

st

1

2

3

100

81

CONSENT FORM By signing this form, I agree that: Yes No The study has been explained to me. All of my questions were answered. Possible harm and discomforts and possible benefits (if any) of this study have been explained to me.

I understand that I have the right not to participate and the right to stop at any time.

I understand that I may refuse to participate without consequence to continuing care at the Faculty.

I have a choice of not answering any specific questions. I am free now, and in the future, to ask any questions about the study. I have been told that my personal information will be kept confidential. I understand that no information that would identify me, will be released or printed without asking me first.

I understand that I will receive a signed copy of this consent form. I hereby consent to participate. ______________________________ ________________ Signature Date Name of Participant and Age: ____________________________________ Telephone #: ____________________________________ Name of person who obtained consent: ___________________________ ____________________________ __________________ Signature Date

82

Appendix 4

Observer Calibration PowerPoint Exercise

83

84

85

86

Appendix 5

Sample Observer Score Sheet for Identification of Radiographic

Features and Visual Analog Scale

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!!!!0123%E(%F5#="G%1>"G67%H:"G$%IF1HJ%%"#%($!%!&/09#$!>$,1/(%#!)%&)!+%,*!%#209!1)$!52##2?/09!#/0$!1)%1!,$',$&$01&!:26,!'$,($/>$8!/+%9$!@6%#/1:!25!1)/&!(20$!3$%+!AB!>2#6+$7!!!!!

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87

Appendix 6

Translating Exposure to Risk: Calculations

A. Background radiation equivalency for temporomandibular joint cone beam CT

imaging techniques

Annual background effective radiation dose: 3.1mSv (3100 Sv)

Daily background effective radiation dose: 3100 Sv / 365 = 8.5 Sv

Hitachi CB MercuRay effective radiation dose (100kVp/10mA): 223.6 Sv

223.6 Sv / 8.5 Sv background dose/day = 26.3 days

Bilateral Kodak 9000 3D effective radiation dose using standard adult acquisition

parameters (70kVp/10mA): 20.5 Sv

20.5 Sv / 8.5 Sv background dose/day = 2.4 days

B. Estimated population risk of carcinogenesis per one million exposures

associated with temporomandibular joint cone beam CT imaging techniques

Risk coefficient for radiation-induced carcinogenesis: 0.055 events/Sv, where one

of fatal cancer

Hitachi CB MercuRay effective radiation dose: 223.6 Sv (2.236E-4Sv)

0.055 events/Sv * 2.236E-4Sv * 1,000,000 exposures 12 cases of fatal cancer per one

million exposures

Bilateral Kodak 9000 3D effective radiation dose using standard adult acquisition

parameters: 20.5 Sv (2.05E-5Sv)

0.055 events/Sv * 2.05E-5Sv * 1,000,000 exposures 1.1 cases of fatal cancer per one

million exposures