Lecture Medical Imaging

8/9/2019 Lecture Medical Imaging

1/85


2/85

Imaging Principles

Objectives for this lecture

To teach the basic principles of diagnosticimaging with

X-rays (planar and CT)

Magnetic Resonance

Ultrasound

Radionuclide (SPECT and PET)


3/85

Imaging Principles

Imaging employs

electromagnetic radiation


4/85

Imaging Principles

Medical Imaging modalitiesMedical Imaging modalities

XX--ray CTray CT (X(X--ray computed tomography) uses ionising radiation,ray computed tomography) uses ionising radiation,

source is external to the body. In some cases, contrast agentssource is external to the body. In some cases, contrast agents areare

injected. Anatomical imagesinjected. Anatomical images

MRIMRI (Magnetic resonance imaging)(Magnetic resonance imaging) uses magnetic fields anduses magnetic fields and

radiofrequency pulses to produce anatomical images. In someradiofrequency pulses to produce anatomical images. In some

cases, contrast agents are injected. Also,cases, contrast agents are injected. Also, fMRIfMRIUSUS (Ultrasound imaging)(Ultrasound imaging) uses high frequency sound waves anduses high frequency sound waves and

the pulse echo effect (which is the basis of radar) to give anatthe pulse echo effect (which is the basis of radar) to give anatomicalomical

information.information.

Nuclear medicine imagingNuclear medicine imaging uses unsealed radioactivity touses unsealed radioactivity toproduce functional imagesproduce functional images


5/85


6/85

Imaging Principles

Planar - X-rayModern direct capture Radiography

Early X-ray apparatus ~ 1920s


7/85

Imaging Principles

X-ray tube


8/85

Imaging Principles

Production of characteristic X-rays


9/85

Imaging Principles

Production of Bremsstrahlung X-rays


10/85

Imaging Principles

Process of Image Production

X-rays produced

X-ray photons are either: Attenuated,

Absorbed, Scattered, Transmitted

air < fat < fluid < soft tissue < bone < metal Transmitted X-ray photons (+some scatter)

reaches the cassette and may interact with:

Intensifying screens (produce light) or Film Latent image (i.e. undeveloped) produced

which is then processed.


11/85

Imaging Principles

Producing a Radiograph


12/85

Imaging Principles

Digital images


13/85

Imaging Principles

Direct Capture Radiography

Direct capture Imaging System No Cassettes

Amorphous Silicate

used as detector material

Similar to digital simulator/

treatment setup


14/85

Imaging Principles

Factors affecting Radiograph

Scatter Distance

Movement kVp and mAs settings


15/85

The normal CXR

First of all is the filmtechnically adequate ?

Correct area imaged

Inspiratory effort

Penetration

Rotation

Annotation


16/85

FUNGAL PNEUMONIA


17/85

TUMOUR


18/85

Aggressive- fibrosarcoma


19/85

Non- aggressive- aneurysmal bone cyst


20/85

Aggressive- Ewings tumour


21/85

Imaging Principles

Fluoroscopy


22/85

Imaging Principles

Computerised X-ray Tomography


23/85

Imaging Principles

Computerised X-ray Tomography


24/85

Imaging Principles

CT numbersLinear attenuation coefficient

= Fraction of energy absorbed Tissue approx CT number

dense bone 1000

Muscle 50

white matter 45

grey matter 40Blood 20

CSF 15

Water 0

Fat -100

Lungs - 200Air - 1000


25/85

Imaging Principles

Radiation doses

CT head 2.5 mSv

CT chest 8 mSv

CT abdomen 10 mSv

CT pelvis 10 mSv

chest radiograph PA 0.02 mSv

abdomen radiograph AP 0.7 mSv

pelvis radiograph AP 0.7 mSv


26/85


27/85

Imaging Principles

Applications of Imaging in Cancer

Diagnosis

Staging

Monitoring response Detection of recurrence


28/85

Imaging Principles

Diagnosis


29/85

Staging local spread


30/85

Imaging Principles

Staging local spread


31/85

Imaging Principles

Staging lymph nodes


32/85

Imaging Principles

Staging distant spread


33/85

Imaging Principles

Magnetic Resonance Imaging

The newest imaging modality

Principle used in spectroscopy since1950s

First human scan 1977

Adopted for clinical use ~ 1988

Approximately 300 in the UK (compared

with approximately 500 CT scanners -which have been around since 1971!)


34/85

Imaging Principles

Magnetic Resonance Imaging

MRI gives superior soft tissue

discrimination compared with CT: largedifferences in signals emitted from different

soft tissues


35/85

Imaging Principles

Principle of MRI

The spinning single proton in a hydrogen atom creates a

magnetic field and each hydrogen atom acts like a tiny magnet


36/85

Imaging Principles

Principle of MRI

In the absence of an external magnetic

field Hydrogen nuclei magnetic momentsare randomly oriented and have a net

magnetization of zero.

In the presence of an external

magnetic field hydrogen protons align

themselves in one of two directions,

parallel or anti-parallel to the netmagnetic field producing a net

magnetic field (Mo)


37/85

Imaging Principles

Precession

The hydrogen atoms are not still but wobble or precess like a

spinning top in the direction of the external magnetic field

Larmor (or precessional) frequency (wO) = B0 x l

Where B0 is the magnetic field and l is the gyromagnetic ratio


38/85


39/85

Imaging Principles

Principles of MRI

When the RF is switched off, the protons:

1. Give up the energy they have absorbed and startto return to their previous direction

2. Start to precess out of frequency

With the result that Longitudinal magnetization gradually increases -

called T1 recovery

Transverse magnetization gradually decreases -called T2 decay


40/85

Imaging Principles

T1 and T2

The rate at which these processes occur vary from tissue to tissue


41/85


42/85

Signal intensities on T1

Imaging Principles

High: Fat, bone marrow, contrast agents

Intermediate: Soft Tissues

Low: Water (urine, CSF)


43/85

Signal intensities on T2

Imaging Principles

High: Fat, Water

Intermediate: Soft tissue

Low: Tendons


44/85

Imaging Principles

MR contrast agents

The most common contrast agents are Gadolinium chelates (DOTA,

DTPA, DO3A etc) which interact with the water molecules in its vicinity

to produce white areas in T1 weighted images

T2 T1 +Gd


45/85

Ovarian Cancer within endometrial cyst

Imaging Principles

Pre -Gd Post Gd


46/85

Iron-oxide particles-darken on T2

Imaging Principles

Benign

Malignant


47/85

Mn-DPDP brightens liver on T1

Imaging Principles

T1 T1 + Teslascan

Manganese(II)-dipyridoxal diphosphate (Mn-DPDP)


48/85


49/85

Di i l d


50/85

Imaging Principles

Diagnostic ultrasound

Ultrasound imaging uses ultra-high-frequency sound waves (3-10 MHz).Human hearing - 20 to 20 000 Hz

a Piezoelectric transducer ( a "crystalline" material such as quartz thatchanges shape when an electric current is applied creating sound wavesand when struck by sound waves creates electrical currents)

ultrasonic waves are emitted by the transducer and travel through human

tissues at a velocity of 1540 m s-1. When the wave reaches an object orsurface with a different texture or acoustic nature, a wave is reflected

back

these echoes are received by the apparatus, changed into electric currentand a 2-D image is produced

more than 20 frames can be generated per second, giving a smooth, real-time image

Di i Ul d


51/85

Imaging Principles

Diagnostic Ultrasound

The stronger the returning signal, the more white it will beon the grey-scale image (hyperechoic = white or light greye.g. fat containing tissues)

hypoechoic = dark grey (e.g. lymphoma, fibroadenoma ofthe breast)

pure fluid gives no echoes, appearing black (anechoic)leading to acoustic enhancementof tissues distal to e.g.gallbladder and urinary bladder

acoustic shadow is the opposite effect where tissues distalto e.g. gas containing areas, gallstones, renal stones receivelittle sound and thus appear as black


52/85

Imaging Principles

Ult d di d t


53/85

Imaging Principles

Ultrasound - disadvantages

interactive modality, operator

dependent

ultrasound waves are greatly

reflected by air-soft tissue and

bone-soft tissue interfaces, thuslimiting its use in the head, chest

and musculoskeletal system

Ultrasound image of gallstone (G) causing accoustic

shadow (S). L = liver

D l Ult d


54/85

Imaging Principles

Doppler Ultrasound

Doppler effect: the influence of a moving object on sound waves

object travelling towards listener causes compression of sound waves (higher

frequency)

object travelling away from listener gives lower frequency

flowing blood causes an alteration to the frequency of the sound wavesreturning to the ultrasound probe, allowing quantitation of blood flow

Colour Doppler shows blood

flowing towards the transducer

as red, blood flowing away as

blue - particularly useful in

echocardiography and

identifying very small blood

vessels

N l M di iN l M di i


55/85

Imaging Principles

.the clinical application.the clinical application

ofof unsealedunsealed radioisotopesradioisotopes

oror radiopharmaceuticalsradiopharmaceuticals

Nuclear MedicineNuclear Medicine

The discovery of RadioactivityThe discovery of Radioactivity


56/85

Imaging Principles

In 1896, Henri Becquerel discovered that uraniumIn 1896, Henri Becquerel discovered that uranium

(and its salts) emitted radiation(and its salts) emitted radiation

2 years later, Pierre and Marie Curie showed that2 years later, Pierre and Marie Curie showed thaturanium rays were an atomic phenomenonuranium rays were an atomic phenomenon

characteristic of the element, and notcharacteristic of the element, and not

related to its chemical or physical state.related to its chemical or physical state.

They called this phenomenonThey called this phenomenon radioactivityradioactivity

Becquerel and the Curies shared the NobelBecquerel and the Curies shared the Nobel

PrizePrize for Physicsfor Physics -- 19031903

y yy y


57/85

Imaging Principles

In 1931, Ernest Lawrence invented theIn 1931, Ernest Lawrence invented the

cyclotron and it became possible tocyclotron and it became possible toproduce artificial radioisotopesproduce artificial radioisotopes

99m99mTc was first produced by a 37 inchTc was first produced by a 37 inch

cyclotron in 1938cyclotron in 1938

the first nuclear medicine scan (the first nuclear medicine scan (131131II--

thyroid) was carried out in 1948 (point bythyroid) was carried out in 1948 (point by

point)point)

Ernest LawrenceErnest Lawrence


58/85

Imaging Principles

planar imaging using an Anger cameraplanar imaging using an Anger camera

-- 19571957

1967 SPET with Anger camera1967 SPET with Anger camera

(rotating the patient on a chair in front of(rotating the patient on a chair in front of

the camera)the camera)

19781978 -- first commercial gammafirst commercial gamma--cameracamera--based SPECT systemsbased SPECT systems

The beginnings of PET (the techniqueThe beginnings of PET (the technique

of counting gammas from positronof counting gammas from positronannhilationannhilation) had come about in 1951) had come about in 1951

and images were produced in 1953and images were produced in 1953

Hal Anger with hisHal Anger with his

invention, theinvention, the

scintillation camerascintillation camera


59/85

Imaging Principles

Nuclear Medicine ImagingNuclear Medicine Imaging

Three types of emissions from radioactiveThree types of emissions from radioactive

isotopes:isotopes: particles,particles, particles andparticles and --rays (alsorays (alsosome associated Xsome associated X--rays)rays)

onlyonly --rays are useful for radioisotope imagingrays are useful for radioisotope imaging(high energy photons)(high energy photons)

In radioisotope imaging, source is inside the bodyIn radioisotope imaging, source is inside the body

(X(X--ray CTray CT source is external).source is external).

Nuclear Medicine


60/85

Imaging Principles

Nuclear Medicine

Radiolabelled tracer (Radiopharmaceutical) is administered

-rays (high energy photons) emitted by the radioisotope aredetected outside the body on a Gamma camera

NaI crystal

Lead collimator

Photomultiplier

tubes

Object

Lead collimators are used to

absorb scattered -rays

-rays impinge on sodium iodide

crystals (dense enough to stop the

photons) and converted into light

which is detected byphotomultipliers.

Photon Detection


61/85

Imaging Principles

Photon Detection

photon is converted by

scintillation crystal to flash oflight

Crystal is coupled to

Photomultiplier Tube

Photocathode converts light toelectron.

Electron avalanche leads to

electronic pulse

HV

Crystal

PM

tube

Gamma-camera Principle


62/85

Imaging Principles

Patient

CollimatorCrystal

Photomultiplier

Acquisition module

Image processor

Gamma camera Principle

Gamma radiation

Functional Imaging


63/85

Imaging Principles

Functional Imaging

Normal distribution of bone function Abnormal distribution

Quantitative


64/85

Imaging Principles

Quantitative

Dynamic acquisition


65/85

Dynamic MAGDynamic MAG--3 kidney transplant study3 kidney transplant study


66/85

Imaging Principles

Tomographic acquisition (SPECT)


67/85

Imaging Principles

Tomographic acquisition (SPECT)

Myocardial perfusion


68/85

Imaging Principles

Myocardial perfusion

3-D Rendering


69/85

Imaging Principles

3 D Rendering

SYSTOLE DIASTOLE

Beating mouse heart


70/85

g

Imaging Principles

Positron Emission Tomography (PET)


71/85

Imaging Principles

g p y ( )


72/85

Imaging Principles

PET coincidence detection


73/85

Imaging Principles

bismuth germanate (BGO) or

Lutetium Oxyorthoscilicate (LSO) crystals

No collimators

High sensitivity

Picomolar concentrations

Absolute quantification (moles per microlitre)

Fluorodeoxyglucose -FDG


74/85

Imaging Principles

yg

Substrate for glucose transporters

undergoes phosphorylation

No further metabolism

FDG shows increased tumour uptake


75/85

Imaging Principles

Head and Neck

Lung cancer


76/85


77/85

Imaging Principles

Glucose metabolism is very low on the first PET studyGlucose metabolism is very low on the first PET study

GdGd contrast MRIcontrast MRI FDGFDG--PETPET Image overlayImage overlay


78/85

Imaging Principles

FDGFDG--PET uptake has increased three months later.PET uptake has increased three months later.

This suggestsThis suggests tumortumorrecurrence, and effectively rules outrecurrence, and effectively rules out

radiation necrosis.radiation necrosis.

GdGd contrast MRIcontrast MRI FDGFDG--PETPET Image overlayImage overlay


79/85


80/85

Imaging Principles

Comparison of PET and SPECTComparison of PET and SPECT

Biological isotopes can be used for PETBiological isotopes can be used for PET


81/85

Imaging Principles

High sensitivity (arising from coincidence detection) and betterHigh sensitivity (arising from coincidence detection) and better

image resolutionimage resolution

Collimators essential for SPECT (much of signal is lost)Collimators essential for SPECT (much of signal is lost)

Attenuation correction in PET is simpleAttenuation correction in PET is simple -- in SPECT it isin SPECT it is v.complexv.complex

PET can be quantitativePET can be quantitative

FastFast -- detector ring in PET collects much more of the signal anddetector ring in PET collects much more of the signal andno need for gantry rotationno need for gantry rotation

HoweverHowever

SPECT is much more commonplace and is cheaper than PETSPECT is much more commonplace and is cheaper than PET

Access to a local cyclotron essential in PETAccess to a local cyclotron essential in PET


82/85

Imaging Principles

PET-CT - The best of both worlds


83/85

Imaging Principles

Combines functionalinformation from PET

with anatomical

location provided byCT

PET-CT


84/85

Imaging Principles


85/85

Imaging Principles

PET/CT shows an area of increased

uptake in the left nasopharynx and

physiologic increased uptake inferior

oral cavity and tongue.

Lecture Medical Imaging

Documents

Transcript of Lecture Medical Imaging