Computed Radiography: Acceptance Testing and Quality Control

11

Computed Radiography:Computed Radiography:Acceptance TestingAcceptance Testing

and and Quality ControlQuality Control

J. Anthony Seibert, Ph.D.J. Anthony Seibert, Ph.D.University of California DavisUniversity of California Davis

Department of RadiologyDepartment of RadiologySacramento, CaliforniaSacramento, California

IntroductionIntroductionCR is the primary means to capture 2D CR is the primary means to capture 2D

images in a PACS environmentimages in a PACS environment

•• Acceptance testingAcceptance testing validates performancevalidates performance

•• Quality controlQuality control verifies optimal operationverifies optimal operation

Considerations:Considerations:•• Knowledge of CR attributes and operationKnowledge of CR attributes and operation•• Understanding the testsUnderstanding the tests•• Determining appropriate resultsDetermining appropriate results

Presentation OutlinePresentation Outline

Overview of CROverview of CRHow does it work? How does it work? What are the issues?What are the issues?

Quality control Quality control When ? When ? What? What? How often? How often?

Acceptance test proceduresAcceptance test proceduresWhat tests? Why? What tests? Why? How? How?

Computed Radiography (CR)Computed Radiography (CR)...is the generic term applied to an imaging system ...is the generic term applied to an imaging system

comprised of:comprised of:

Photostimulable Storage PhosphorPhotostimulable Storage Phosphorto acquire the xto acquire the x--ray projection imageray projection image

CR ReaderCR Readerto extract the electronic latent imageto extract the electronic latent image

Digital electronicsDigital electronicsto convert the signals to digital formto convert the signals to digital form

CR Image AcquisitionCR Image Acquisition

Phosphor platePhosphor plate

XX--rayraysystemsystem

1.1. XX--ray Exposureray Exposure

ImageImageScalingScaling

3.3.ImageImageRecordRecord

4.4.

PatientPatientComputedComputedRadiographRadiograph

5.5.unexposedunexposed

ImageImageReaderReader

2.2.

exposedexposed

Charge Charge collection collection

devicedevice

XX--ray converterray converterxx--rays rays →→ electronselectrons

Transmitted xTransmitted x--raysraysthrough patientthrough patient

Analog to DigitalConversion

Analog to DigitalAnalog to DigitalConversionConversion

1. Acquisition1. Acquisition

2. Display2. Display

3. Archiving3. Archiving

Digital Digital processingprocessing

Digital to AnalogConversion

Digital to AnalogDigital to AnalogConversionConversion

Digital PixelDigital PixelMatrixMatrix

Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.

22

Film laser printerFilm laser printer

DICOMDICOM

PACS SoftPACS Soft--copy reviewcopy reviewCR CR -- QC WorkstationQC Workstation

CRCRReaderReader

CR NetworkingCR Networking

•• PACS and DICOMPACS and DICOM–– Digital Imaging Digital Imaging COmmunicationsCOmmunications in Medicinein Medicine–– Provides standard for modality interfaces, Provides standard for modality interfaces,

storage/retrieval, and printstorage/retrieval, and print

•• Modality Worklist Input (from RIS via HLModality Worklist Input (from RIS via HL--7)7)

•• Technologist QC WorkstationTechnologist QC Workstation–– Image manipulation and processingImage manipulation and processing–– Processed / Unprocessed imagesProcessed / Unprocessed images

•• DICOM image outputDICOM image output

Photostimulated LuminescencePhotostimulated LuminescenceConduction bandConduction band

Valence bandValence band

PSLPSL3.0 eV3.0 eV

t t EuEu

EuEu 2+2+EuEu 3+3+//4f 4f 77

8.3 eV8.3 eVLaser Laser

stimulationstimulation

2.0 eV2.0 eV

F/FF/F++

PSLC complexes (F centers) are created in PSLC complexes (F centers) are created in numbers proportional to incident xnumbers proportional to incident x--ray ray intensityintensity

ee--

t t tunnelingtunneling

t t recombinationrecombination

4f 4f 66 5d5d

phononphonon

CR: How does it work?CR: How does it work?

IncidentIncidentxx--rays rays

ee

Energy Band Energy Band BaFBrBaFBr

300300400400500500600600700700800800

Rela

tive

inte

nsity

Rela

tive

inte

nsity

0.00.0

0.50.5

1.01.0

λλ (nm)(nm)

Energy (eV)Energy (eV)33 442.52.5221.51.5

Stimulation and Emission SpectraStimulation and Emission Spectra

1.751.75

EmissionEmissionStimulationStimulation

DiodeDiode680 nm680 nm

BaFBr: EuBaFBr: Eu2+2+

OpticalOpticalBarrierBarrier

Photostimulated LuminescencePhotostimulated Luminescence

Incident Laser BeamIncident Laser Beam

PMTPMT

Protective LayerProtective Layer

Phosphor LayerPhosphor Layer

Base SupportBase Support

LightLightScatteringScattering

Laser Light SpreadLaser Light Spread

PhotostimulatedPhotostimulatedLuminescenceLuminescence

"Effective" readout diameter"Effective" readout diameter

ExposedExposedImagingImaging

PlatePlate

Light guideLight guidePSLPSLSignalSignal

CR: Latent Image ReadoutCR: Latent Image Readout

PMTPMT

Polygonal Polygonal MirrorMirror

LaserLaserSourceSource

Light channeling guideLight channeling guide

Output SignalOutput Signal

ReferenceReferencedetectordetector Cylindrical mirrorCylindrical mirror

ff--θθlenslens

ADCADC

Laser beam: Laser beam: Scan directionScan direction

Plate translation: Plate translation: SubSub--scan directionscan direction

To imageTo imageprocessorprocessor

ADCADC

x= 1279x= 1279y= 1333y= 1333z= 500z= 500

Computed Radiography: Acceptance Testing and Quality Control -- J.A. Seibert, Ph.D.

33

Scan DirectionScan Direction

SubSub--scan Directionscan Direction

Laser beam deflectionLaser beam deflection

Plate translationPlate translation

Typical CR resolution:Typical CR resolution:35 x 43 cm 35 x 43 cm ---- 2.5 lp/mm (200 2.5 lp/mm (200 µµm)m)24 x 30 cm 24 x 30 cm ---- 3.3 lp/mm (150 3.3 lp/mm (150 µµm)m)18 x 24 cm 18 x 24 cm ---- 5.0 lp/mm (100 5.0 lp/mm (100 µµm)m)

Screen/film resolution:Screen/film resolution:77--10 lp/mm (80 10 lp/mm (80 µµm m -- 25 25 µµm)m)

Phosphor Plate CyclePhosphor Plate Cycle

PSP PSP

Base supportBase support

reusereuse

plate erasure:plate erasure:remove residualsremove residuals

light erasurelight erasure

plate exposure:plate exposure:create latent imagecreate latent image

xx--ray exposureray exposure

plate readout:plate readout:extract latent imageextract latent image

laser beam scanlaser beam scan

Computed RadiographyComputed Radiography

•• Acquisition, Display and Archive are Acquisition, Display and Archive are separateseparatefunctionsfunctions

•• Variable speed detectorVariable speed detector–– 20 to 2000 speed 20 to 2000 speed

•• Wide dynamic rangeWide dynamic range–– 0.01 to 100 mR0.01 to 100 mR

•• Image processing is a Image processing is a crucialcrucial requirement requirement

Exposure Latitude: Dynamic RangeExposure Latitude: Dynamic Range

FilmFilmFilm

100:1100:1100:1

Log relative exposureLog relative exposure

Sign

al o

utpu

tSi

gnal

out

put

10000:110000:110000:1

CRCRCR

Raw imageRaw image

•• Inherent subject Inherent subject contrast displayedcontrast displayed

•• Contrast inverted Contrast inverted (to screen(to screen--film)film)

•• PSL signal amplitude PSL signal amplitude log amplifiedlog amplified

Processing the ImageProcessing the Image

•• Image preImage pre--processingprocessing–– Find pertinent image information (histogram analysis)Find pertinent image information (histogram analysis)–– Scale data to an appropriate rangeScale data to an appropriate range

•• Contrast enhancementContrast enhancement–– Anatomy specific grayscale manipulationAnatomy specific grayscale manipulation

•• Spatial frequency enhancementSpatial frequency enhancement


44

Finding the Image LocationFinding the Image Location

•• Image recognition phaseImage recognition phase–– Collimation (Agfa)Collimation (Agfa)

–– EDR, automatic mode (Fuji)EDR, automatic mode (Fuji)

–– Segmentation (Kodak)Segmentation (Kodak)

•• Finding collimation borders and edgesFinding collimation borders and edges

Histogram analysisHistogram analysis

•• Frequency distribution of pixel values within a Frequency distribution of pixel values within a defined area in the imagedefined area in the image

•• Shape is anatomy specificShape is anatomy specific

•• Sets minimum and maximum “useful” pixel valuesSets minimum and maximum “useful” pixel values

Histogram:Histogram:frequency distribution of pixel values in an imagefrequency distribution of pixel values in an image

ValueValue

Freq

uenc

yFr

eque

ncy

Histogram DistributionHistogram Distribution

33

222222

2222

222222

444444

4444

4444

4444

444444

1111

1111

0000 11 22 33 44 55

224466881010121214141616

ValueValue

Freq

uenc

yFr

eque

ncy


The shape is dependent on radiographic study, The shape is dependent on radiographic study, positioning and techniquepositioning and technique

AnatomyAnatomy

Freq

uenc

yFr

eque

ncy

Useful signalUseful signal

Collimated Collimated areaarea

Direct Direct xx--ray ray areaarea

Pixel valuePixel value


Digital Digital valuevalue

Freq

uenc

y of

Fr

eque

ncy

of

Dig

ital N

umbe

rD

igita

l Num

ber

0.01mR0.01mR 0.1mR0.1mR 1mR1mR 10mR10mR 100mR100mR

511511

10231023

00Q1Q1

S1S1

Q2Q2

S2S2

Sensitivity (S)Sensitivity (S)2000020000 20002000 200200 2020 22

SSKK

Latitude (L)Latitude (L)


55

Data conversionData conversionExposure into digital numberExposure into digital number

00 511511 102310231010331010--11 101000 101022101011

Exposure inputExposure input

Rel

ativ

e PS

LR

elat

ive

PSL

Raw Digital OutputRaw Digital Output

101011

1010--11

101000

101022

Input to output digital Input to output digital numbernumber

Input digital numberInput digital number200200 600600 1,0001,00000

200200

400400

600600

800800

1,0001,000

Out

put

digi

tal n

umbe

rO

utpu

t di

gita

l num

ber

Grayscale transformationGrayscale transformation

HistogramHistogram

Find the Find the signal signal

minmin maxmax

1.1. Scale toScale torange range

2.2. Create film Create film looklook--alikealike

3.3.

Histogram: pediatric imageHistogram: pediatric image

0

200

400

600

800

0 400 600 800 1000 Digital value

Freq

uenc

y

to 8323to 9368

Useful image range for anatomyUseful image range for anatomy

200

PrePre--processed processed “raw” image“raw” image

Scaled and inverted:Scaled and inverted:“unprocessed” image“unprocessed” image

Data conversion for overexposureData conversion for overexposureExposure into digital numberExposure into digital number

ExposureExposureinputinput

Rel

ativ

e PS

LR

elat

ive

PSL

00 511511 10231023


(scaled and log amplified)(scaled and log amplified)

Reduce overall gain Reduce overall gain

1010331010--11 101000 101022101011

101011

1010--11

101000

101022

minmin maxmaxoverexposureoverexposure

Screen-Film

Underexposed Overexposed

Computed Radiography

Underexposed Overexposed


66

Data conversion for wide latitudeData conversion for wide latitudeExposure into digital numberExposure into digital number

Rel

ativ

e PS

LR

elat

ive

PSL

101011

1010--11

101000

101022

00 511511 10231023


(scaled and log amplified)(scaled and log amplified)

ExposureExposureinputinput 1010331010--11 101000 101022101011

Change gradientChange gradient(auto mode)(auto mode)

low kVplow kVp(wide range)(wide range)

minmin maxmax

ScreenScreen--FilmFilm80 kVp, 18 mAs80 kVp, 18 mAs 80 kVp, 64 mAs80 kVp, 64 mAs

CRCR80 kVp, 18 mAs80 kVp, 18 mAs

L=4, wide latitudeL=4, wide latitude400 speed screen 400 speed screen -- filmfilm

Contrast EnhancementContrast Enhancement

•• Optimize image contrast via Optimize image contrast via nonnon--linearlineartransformation curvestransformation curves

•• Unprocessed images display linear “subject contrast”Unprocessed images display linear “subject contrast”–– “Gradation processing” (Fuji)“Gradation processing” (Fuji)–– “Tone scaling” (Kodak)“Tone scaling” (Kodak)–– “MUSICA” (Agfa)“MUSICA” (Agfa)

LookLook--upup--table transformationtable transformation

Input digital numberInput digital number

Ou

tpu

t di

gita

l nu

mbe

rO

utp

ut

digi

tal n

um

ber

00 200200 400400 600600 800800 1,0001,00000

200200

400400

600600

800800

1,0001,000

AAEELLMM

Fuji SystemFuji SystemExample LUTsExample LUTs

GTGTGradient TypeGradient Type

RawRaw UnprocessedUnprocessed Contrast EnhancedContrast Enhanced

Spatial frequencySpatial frequency

Original MTFOriginal MTF

Resp

onse

Resp

onse

lowlow highhigh

Spatial Frequency ProcessingSpatial Frequency Processing

“Edge Enhancement”“Edge Enhancement”


Solid: original responseSolid: original response

Dash: low pass filteredDash: low pass filtered

Resp

onse

Resp

onse

lowlow highhigh


Original Original -- filteredfiltered

Difference:Difference:

lowlow highhigh


SumSum

lowlow

Difference + OriginalDifference + Original

Edge Enhanced:Edge Enhanced:

highhigh

OriginalOriginal BlurredBlurred

DifferenceDifference Edge enhancedEdge enhanced


77

Anatomy LUT shape parametersFrequency enhancement

parameters

Fuji CR Parameter Settings

Anatomical regionAnatomical region GAGA GTGT GCGC GSGS RNRN RTRT REREGeneral chest (LAT)General chest (LAT) 1.01.0 BB 1.61.6 --0.20.2 4.04.0 RR 0.20.2General chest (PA)General chest (PA) 0.60.6 DD 1.61.6 --0.50.5 4.04.0 RR 0.20.2Port Chest GRIDPort Chest GRID 0.80.8 FF 1.81.8 --0.050.05 4.04.0 TT 0.20.2Port Chest NO GRIDPort Chest NO GRID 1.01.0 DD 1.61.6 --0.150.15 4.04.0 RR 0.50.5PedsPeds chest NICU/PICUchest NICU/PICU 1.11.1 DD 1.61.6 --0.20.2 3.03.0 RR 0.50.5FingerFinger 0.90.9 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5WristWrist 0.80.8 OO 0.60.6 0.20.2 5.05.0 TT 0.50.5ForearmForearm 0.80.8 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5Plaster cast (arm)Plaster cast (arm) 0.80.8 OO 0.60.6 0.40.4 5.05.0 TT 0.50.5Elbow*Elbow* 0.80.8 OO 0.60.6 0.40.4 7.07.0 TT 1.01.0Upper Ribs*Upper Ribs* 0.80.8 OO 1.61.6 0.00.0 5.05.0 RR 1.01.0Pelvis*Pelvis* 0.90.9 OO 0.60.6 0.20.2 6.06.0 TT 1.01.0Pelvis portablePelvis portable 0.90.9 OO 0.60.6 0.20.2 4.04.0 TT 0.50.5TibTib/Fib/Fib 0.90.9 NN 0.60.6 0.250.25 5.05.0 FF 0.50.5FootFoot 0.80.8 OO 0.60.6 0.30.3 5.05.0 TT 0.50.5Foot*Foot* 1.21.2 NN 0.60.6 --0.050.05 7.07.0 TT 0.50.5OsOs CalcisCalcis 0.80.8 OO 0.60.6 0.40.4 5.05.0 FF 1.01.0Foot castFoot cast 0.80.8 OO 0.60.6 0.50.5 5.05.0 FF 0.50.5CC--spine spine 1.11.1 FF 0.60.6 0.50.5 5.05.0 PP 0.50.5TT--spinespine 0.80.8 FF 1.81.8 --0.050.05 4.04.0 TT 0.20.2SwimmersSwimmers 1.21.2 JJ 0.90.9 0.30.3 5.05.0 TT 0.50.5Lumbar spineLumbar spine 1.01.0 NN 0.90.9 0.40.4 5.05.0 TT 1.01.0Breast specimenBreast specimen 2.52.5 DD 0.60.6 0.350.35 9.09.0 PP 1.01.0

Acceptance Test / QC considerationsAcceptance Test / QC considerations

•• Image acquisitionImage acquisition

•• ElectroElectro--Mechanical readoutMechanical readout

•• Image processingImage processing

•• PACS / RIS interfacesPACS / RIS interfaces

•• Image handlingImage handling

Recommended Acceptance TestsRecommended Acceptance Tests

•• Physical InspectionPhysical Inspection––InventoryInventory––PACS Interfaces PACS Interfaces

•• Imaging Plate Uniformity and Dark NoiseImaging Plate Uniformity and Dark Noise

•• Signal Response: Linearity and SlopeSignal Response: Linearity and Slope

•• Signal Response: Exposure calibration and Signal Response: Exposure calibration and beam qualitybeam quality

•• Laser Beam Function Laser Beam Function

•• High Contrast ResolutionHigh Contrast Resolution

Recommended Acceptance TestsRecommended Acceptance Tests

•• Noise / LowNoise / Low--Contrast ResponseContrast Response

•• DistortionDistortion

•• Erasure ThoroughnessErasure Thoroughness

•• Artifact Analysis: Hardware/Software Artifact Analysis: Hardware/Software

•• Positioning and collimation robustnessPositioning and collimation robustness

•• Imaging Plate ThroughputImaging Plate Throughput

Acceptance test tools requiredAcceptance test tools required

•• Exposure meter/dosimeterExposure meter/dosimeter

•• Spatial resolution phantomSpatial resolution phantom

•• Low contrast phantomLow contrast phantom

•• Vendor QC phantom (periodic tests)Vendor QC phantom (periodic tests)

•• SMPTE test patternSMPTE test pattern

•• Anthropomorphic phantomAnthropomorphic phantom

•• Documentation log / spreadsheet / instructionsDocumentation log / spreadsheet / instructions

CR: Spatial ResolutionCR: Spatial Resolution

•• Phosphor plate sizes: impact on resolutionPhosphor plate sizes: impact on resolution

35x43 (14x17)35x43 (14x17)

0.2 mm pixels0.2 mm pixels

24x30 (10x12)24x30 (10x12)

0.14 mm pixels0.14 mm pixels 0.1 mm pixels0.1 mm pixels

18x24 (8x10)18x24 (8x10)


88

High Contrast (Spatial) ResolutionHigh Contrast (Spatial) Resolution18 x 24 cm18 x 24 cm 35 x 43 cm35 x 43 cm MTF Curves MTF Curves

00 22 44 66 88 101000

0.20.2

0.40.4

0.60.6

0.80.8

11

Spatial Frequency (lp/mm)Spatial Frequency (lp/mm)

MTF

MTF

Standard CRStandard CR

Hi Hi res res CRCR

ScreenScreen--filmfilm

SampledSampled MTF:MTF:Standard CRStandard CR2K x 2K matrix2K x 2K matrix35 x 43 cm35 x 43 cm

SubscanSubscanScanScan

PrePre--sampledsampledMTFMTF

XX--ray Absorption Efficiencyray Absorption Efficiency

00 2020 4040 6060 8080 100100 120120 14014000

0.20.2

0.40.4

0.60.6

0.80.8

11

Energy (keV)Energy (keV)

Phot

on a

bsor

ptio

n fra

ctio

nPh

oton

abs

orpt

ion

fract

ion

GdGd22OO22S, 120 mg/cmS, 120 mg/cm22

BaFBr, 50 mg/cm²BaFBr, 50 mg/cm²

BaFBr, 100 mg/cm²BaFBr, 100 mg/cm²

Low Contrast Response: Leeds TOLow Contrast Response: Leeds TO--1616

0.5 mR0.5 mR3.5 mR3.5 mR 70 kVp70 kVp

10 mAs10 mAs 20 mAs20 mAs

UniformityUniformity

498498 508508

490490

497497 505505

537537

487487544544

513513

480480


99

Radiation Dose for CRRadiation Dose for CR

•• Variable Speed DetectorVariable Speed Detector

•• Optimal doseOptimal dose (UC Davis)(UC Davis)–– Adult chest image: Adult chest image: S=200S=200--300300–– Neonates/pediatrics: Neonates/pediatrics: S=400S=400--600600–– Extremities:Extremities: S= 75S= 75--100100

–– Lower detection efficiency, luminance and readout noiseLower detection efficiency, luminance and readout noise

•• AntiAnti--scatter grids neededscatter grids needed

Sensitivity number, SSensitivity number, S

•• Estimate of the incident exposure on the IPEstimate of the incident exposure on the IP

•• Comparable to screenComparable to screen--film “speed”film “speed”

•• Amplification required to map median value of Amplification required to map median value of histogram to 511 (0 to 1023 grayscale)histogram to 511 (0 to 1023 grayscale)

•• Dependent on histogram shape Dependent on histogram shape andand examination examination selectedselected

Date: 7/10/98 Location: UCDMC, ACC, 3 Medical Physicist: Anthony Seibert, Ph.D. System Identification: CR unit 3

UC Davis Medical CenterCR Reader and Screens

Signal Response: Calibration and Beam Quality

Note: Use mAs values to provide an approximate exposure of 1 mR to the IP.

Menu = TEST Exposure ConditionsIP Type: ST 14x17 SubMenu = Ave 2.0 Focal spot Time delay SID (cm) SMD (cm)

IP SN: L = 2, EDR = semi 1.2 mm ~2 min 140 130

kVp DependencykVp Filtration mAs mR-meter mR-IP S S (1mR) OD NA60 1 Al/0.5 Cu 15.00 1.06 0.91 121.00 110.59 1.41 NA80 1 Al/0.5 Cu 4.5 1.06 0.91 108.00 98.71 1.38 NA115 1 Al/0.5 Cu 1.13 1.14 0.98 115.00 113.04 1.45 NA

Maximum Difference: 14.33 0.07 NAFiltration Dependency

kVp Filtration mAs mR-m eter mR-IP S S (1mR) OD NA80 none 0.50 0.96 0.83 187.00 154.79 1.40 NA80 1 Al/0.5 Cu 4.50 1.06 0.91 108.00 98.71 1.38 NA80 1Al/2.5Cu 60.00 0.99 0.85 124.00 105.85 1.40 NA

Maximum Difference: 56.08 0.02 NA

0.00

20.00

40.00

60.00

80.00

100.00

120.00

50 70 90 110 130kVp

Resp

onse

S (1mR)

0.0020.0040.0060.0080.00

100.00120.00140.00160.00180.00

none 1 Al/0.5 Cu 1Al/2.5CuFiltration

Res

pons

e

S (1mR)



Signal Response: Calibration and Beam Quality

Note: Use mAs values to provide an approximate exposure of 1 mR to the IP.

Menu = TEST Exposure ConditionsIP Type: ST 14x17 SubMenu = Ave 2.0 Focal spot Time delay SID (cm) SMD (cm)

IP SN: L = 2, EDR = semi 1.2 mm ~2 min 140 130

kVp DependencykVp Filtration mAs mR-meter mR-IP S S (1mR) OD NA60 1 Al/0.5 Cu 15.00 1.06 0.91 121.00 110.59 1.41 NA80 1 Al/0.5 Cu 4.5 1.06 0.91 108.00 98.71 1.38 NA115 1 Al/0.5 Cu 1.13 1.14 0.98 115.00 113.04 1.45 NA

Maximum Difference: 14.33 0.07 NAFiltration Dependency

kVp Filtration mAs mR-m eter mR-IP S S (1mR) OD NA80 none 0.50 0.96 0.83 187.00 154.79 1.40 NA80 1 Al/0.5 Cu 4.50 1.06 0.91 108.00 98.71 1.38 NA80 1Al/2.5Cu 60.00 0.99 0.85 124.00 105.85 1.40 NA

Maximum Difference: 56.08 0.02 NA

0.00

20.00

40.00

60.00

80.00

100.00

120.00

50 70 90 110 130kVp

Resp

onse

S (1mR)

0.0020.0040.0060.0080.00

100.00120.00140.00160.00180.00

none 1 Al/0.5 Cu 1Al/2.5CuFiltration

Res

pons

e

S (1mR)

Guidelines for QC based on ExposureGuidelines for QC based on Exposure

•• >1000>1000 <0.2 mR<0.2 mR

•• 600 600 –– 10001000 0.30.3--0.2 mR0.2 mR

•• 300 300 -- 600600 1.01.0--0.3 mR0.3 mR

•• 150 150 -- 300300 1.31.3--1.0 mR1.0 mR

•• 75 75 --150150 1.31.3--2.7 mR2.7 mR

•• 50 50 -- 7474 4.04.0--2.7 mR2.7 mR

•• <50<50 >4.0 mR>4.0 mR

•• Underexposed: repeatUnderexposed: repeat

•• Underexposed: QC exceptionUnderexposed: QC exception

•• Underexposed: QC reviewUnderexposed: QC review

•• Acceptable rangeAcceptable range

•• Overexposed: QC reviewOverexposed: QC review

•• Overexposed: QC exceptionOverexposed: QC exception

•• Overexposed: repeatOverexposed: repeat

Sensitivity numberSensitivity number IndicationIndication

Sensitivity number, SSensitivity number, S

•• Imaging plate (HR vs. ST) differencesImaging plate (HR vs. ST) differences

•• Examination specific histogram shapesExamination specific histogram shapes–– S number varies with examination type S number varies with examination type

•• EDR mode effectsEDR mode effects–– Automatic (determines S1 and S2 values on histogram)Automatic (determines S1 and S2 values on histogram)–– SemiSemi--automatic (average value within ROI)automatic (average value within ROI)–– Fixed (system acts like screenFixed (system acts like screen--film detector)film detector)

•• XX--ray beam spectrum effectsray beam spectrum effects–– S number varies with beam hardness (calibration required)S number varies with beam hardness (calibration required)

What S value is appropriate?What S value is appropriate?

•• Determined by examination Determined by examination UCDMC targetsUCDMC targets–– Adult exams (CXR, abdomen, etc) Adult exams (CXR, abdomen, etc) 150 150 –– 300300–– Extremities Extremities (ST plates) (ST plates) 75 75 –– 150150–– PediatricsPediatrics 300 300 –– 600600

•• CR’sCR’s variable speed should be used to advantagevariable speed should be used to advantage

•• Anatomical information can be lost with too high or too Anatomical information can be lost with too high or too low exposurelow exposure


1010

Adult portable chest calculated exposuresAdult portable chest calculated exposuresFirst half, 1994, 4572 examsFirst half, 1994, 4572 exams

Incident ExposureIncident ExposureLowLow HighHigh

500

500

400

400

300

300

200

200

100

100

<50

<50

00

100100

200200

300300

400400

500500

600600

System speed (S #)System speed (S #)

#ex

ams

#ex

ams

38.3% 53.9% 7.8%38.3% 53.9% 7.8%

Target Target exposure exposure rangerange

Q1Q1

Q2Q2Q3Q3

Q4Q4

Adult portable chest calculated exposuresAdult portable chest calculated exposuresSecond half, 1994, 4661 examsSecond half, 1994, 4661 exams

23.1% 73.5% 3.4%23.1% 73.5% 3.4%

Target Target exposure exposure rangerange

Incident ExposureIncident ExposureLowLow HighHigh

500

500

400

400

300

300

200

200

100

100

<50

<50

00

100100

200200

300300

400400

500500

600600

System speed (S #)System speed (S #)

#ex

ams

#ex

ams

April 1 April 1 -- 17, 199617, 1996Adult Portable ChestAdult Portable Chest

002020404060608080

100100120120140140160160180180

>1000

>1000

600

600--6

9969

9

500

500--5

4954

9

400

400--4

4944

9

350

350--3

7437

4

300

300--3

2432

4

250

250--2

7427

4

200

200--2

2422

4

150

150--1

7417

4

100

100--1

2412

4

5050--7

474

Sensitivity numberSensitivity number

Num

ber

of e

xam

inat

ions

Num

ber

of e

xam

inat

ions

Grid techniqueGrid techniquewithout a gridwithout a grid

April 1 - 17, 1996April 1 April 1 -- 17, 199617, 1996

Adult Portable ChestAdult Portable ChestAdult Portable Chest

000202020404040606060808080

100100100120120120140140140160160160180180180

>1000

>1000

>1000

600-

699

600

600--6

9969

9

500-

549

500

500--5

4954

9

400-

449

400

400--4

4944

9

350-

374

350

350--3

7437

4

300-

324

300

300--3

2432

4

250-

274

250

250--2

7427

4

200-

224

200

200--2

2422

4

150-

174

150

150--1

7417

4

100-

124

100

100--1

2412

4

50-7

45050

--7474

Sensitivity numberSensitivity numberSensitivity number

Num

ber

of e

xam

inat

ions

Num

ber

of e

xam

inat

ions

Num

ber

of e

xam

inat

ions

“Exposure Creep”“Exposure Creep”“Exposure Creep”

Grid techniquewithout a gridGrid techniqueGrid techniquewithout a gridwithout a grid

Total # repeats = 1043 from Total # repeats = 1043 from Willis, RSNA 1996Willis, RSNA 1996

Positioning46%

Overexposure12%

Underexposure10%

Reprinting9%

Motion6%

Wrong exam5%

Other12% Repeated Repeated

Examinations with CRExaminations with CR

Radiation Dose for CRRadiation Dose for CR

•• Variable Speed DetectorVariable Speed Detector

•• Optimal doseOptimal dose for typical adult chest image is 2X higherfor typical adult chest image is 2X higherthan 400 speed screen/filmthan 400 speed screen/film

–– Lower absorption efficiencyLower absorption efficiency

–– Quantum and electronic noiseQuantum and electronic noise

–– Readout inefficiencies of latent imageReadout inefficiencies of latent image

•• AntiAnti--scatter grids necessary for most proceduresscatter grids necessary for most procedures

AEC adjustment proceduresAEC adjustment procedures•• A 200A 200--speed equivalent exposure is desirablespeed equivalent exposure is desirable

•• Empirically determine AEC setting(s) with simple uniform Empirically determine AEC setting(s) with simple uniform phantomsphantoms

•• UCDMC technique: use “fixed” mode (S=200) and sensitivity test UCDMC technique: use “fixed” mode (S=200) and sensitivity test menu; adjust AEC response according to changes in film optical menu; adjust AEC response according to changes in film optical densitydensity

•• Verify settings with semiVerify settings with semi--auto modeauto mode

•• Verify patient exposure “S” number; recheck oftenVerify patient exposure “S” number; recheck often


1111



Inspection Results Summary

Acceptab le1. Physical Inspection - Inventory Yes2. Imaging Plate Uniformity and Dark Noise Yes3. Signal Response: Linearity and Slope Yes4. Signal Response: Calibration and Beam Quality Yes5. Laser Beam Function Yes6. High-Contrast Resolution Yes7. Noise/Low-Contrast Response Yes8. Distortion Yes9. Erasure Thoroughness Yes*

10. Anti-Aliasing Yes11. Positioning and Collimation Errors Yes12. Throughput Yes

Comments:



Inspection Results Summary

Acceptab le1. Physical Inspection - Inventory Yes2. Imaging Plate Uniformity and Dark Noise Yes3. Signal Response: Linearity and Slope Yes4. Signal Response: Calibration and Beam Quality Yes5. Laser Beam Function Yes6. High-Contrast Resolution Yes7. Noise/Low-Contrast Response Yes8. Distortion Yes9. Erasure Thoroughness Yes*

10. Anti-Aliasing Yes11. Positioning and Collimation Errors Yes12. Throughput Yes

Comments:

•• FilmFilm--based performance measurements based performance measurements

•• Digital image analysis tools and evaluation methods Digital image analysis tools and evaluation methods not readily availablenot readily available

•• Low contrast resolution measurementsLow contrast resolution measurements

•• Lack of a standardized QC phantomLack of a standardized QC phantom

Problem areasProblem areas

Quality ControlQuality Control

Three levels of system performance quality controlThree levels of system performance quality control

1. Routine: Technologist level1. Routine: Technologist level-- no radiation measurementsno radiation measurements

2. Full inspection: Physicist level 2. Full inspection: Physicist level -- radiation measurements and nonradiation measurements and non--invasive adjustmentsinvasive adjustments

3. System adjustment: Vendor service level3. System adjustment: Vendor service level-- hardware and software maintenancehardware and software maintenance

Periodic Quality ControlPeriodic Quality Control

•• Daily (technologist)Daily (technologist)

–– Inspect CR system and status.Inspect CR system and status.

–– Interfaces: PACS broker, ID terminal, QC workstationInterfaces: PACS broker, ID terminal, QC workstation

–– Erase image receptors (if status unknown).Erase image receptors (if status unknown).


•• Weekly / Biweekly (technologist)Weekly / Biweekly (technologist)

–– Calibrate review workstation monitors (SMPTE).Calibrate review workstation monitors (SMPTE).

–– Acquire QC phantom test images. Verify performance.Acquire QC phantom test images. Verify performance.

–– Check filters / vents and clean as necessary.Check filters / vents and clean as necessary.

–– Clean screens with recommended agents.Clean screens with recommended agents.


•• Quarterly (Technologist)Quarterly (Technologist)

–– Inspect cassettes. Clean with recommended agents.Inspect cassettes. Clean with recommended agents.

–– Review image retake rate and exposure trends. Review image retake rate and exposure trends.

–– Update QC log. Review outUpdate QC log. Review out--ofof--tolerance issues.tolerance issues.


1212


•• Annually (Physicist)Annually (Physicist)

–– Perform linearity / sensitivity / uniformity testsPerform linearity / sensitivity / uniformity tests

–– Inspect / evaluate image qualityInspect / evaluate image quality

–– ReRe--establish baseline values (Acceptance Tests)establish baseline values (Acceptance Tests)

–– Review retakes, exposures, service records.Review retakes, exposures, service records.

What is needed?What is needed?

•• Computer friendly phantomsComputer friendly phantoms

•• Objective quantitative analysis methodsObjective quantitative analysis methods

•• System performance tracking and database logsSystem performance tracking and database logs

•• Exposure monitoring tools and database trackingExposure monitoring tools and database tracking

FujiFuji

Single exposure, qualitative Single exposure, qualitative and quantitativeand quantitative

AgfaAgfa

Step wedge (signal, signal to Step wedge (signal, signal to noise and linearity response tests)noise and linearity response tests)

Diagonal bar Diagonal bar (laser jitter test)(laser jitter test)

Notches Notches ((geometricgeometricaccuracyaccuracytests)tests)

Line pair Line pair phantoms phantoms (contrast (contrast transfer tests)transfer tests)

Open area (scan Open area (scan uniformity test)uniformity test)

LumisysLumisys Home builtHome built

Lead attenuatorLead attenuator(dynamic range)(dynamic range)

Copper step wedgeCopper step wedge(dynamic range, linearity, SNR)(dynamic range, linearity, SNR)

Edge for Edge for Presampled Presampled

MTFMTF

ResolutionResolutionBar PatternBar Pattern(qualitative)(qualitative)

FiducialFiducial MarkersMarkers(distance accuracy)(distance accuracy)

40 line/cm grid40 line/cm grid(visual aliasing)(visual aliasing)

Additional Information / HelpAdditional Information / Help

•• AAPM Task Group #10 document:AAPM Task Group #10 document:•• Email: Email: jaseibertjaseibert@@ucdavisucdavis..eduedu

•• Dr. Dr. Ehsan Samei Ehsan Samei spreadsheets spreadsheets –– http://http://deckarddeckard.mc.duke..mc.duke.eduedu/~/~sameisamei/downloads /downloads

•• Vendor efforts for QC phantom development and Vendor efforts for QC phantom development and analysisanalysis

SummarySummary

•• CR is the mainstay for direct digital acquisition of CR is the mainstay for direct digital acquisition of projection radiographsprojection radiographs

•• CR acceptance testing and QC are essential for CR acceptance testing and QC are essential for optimal operationoptimal operation

•• A A TEAMTEAM approach is necessaryapproach is necessary–– Technologists, Radiologists, Physicists, Technologists, Radiologists, Physicists, –– Clinical Engineering, Information System GroupClinical Engineering, Information System Group


Computed Radiography: Acceptance Testing and Quality Control

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