Nuclear Medicine: Nuclear Medicine: Image Quality, Sources of Image Quality, Sources of

Artefacts and the Artefacts and the Nuclear Medicine Nuclear Medicine “What… ?!” Quiz“What… ?!” Quiz

Katrina CockburnKatrina Cockburn

Nuclear Medicine PhysicistNuclear Medicine Physicist

Image Quality in NMImage Quality in NM

Image Quality is largely subjectiveImage Quality is largely subjective Beware of believing pretty = better!Beware of believing pretty = better!

Can measure physical properties:Can measure physical properties: ResolutionResolution Noise (inc. SNR)Noise (inc. SNR) ContrastContrast

Can qualitatively score “aesthetic” Can qualitatively score “aesthetic” propertiesproperties

Physical Measures of Image Physical Measures of Image QualityQuality

Spatial ResolutionSpatial Resolution Smallest separation between two point Smallest separation between two point

sources which will permit them to be sources which will permit them to be distinguished as two distinct sourcesdistinguished as two distinct sources

NoiseNoise Statistical uncertainty in the number of counts Statistical uncertainty in the number of counts

recordedrecorded ContrastContrast

Differences in intensity in parts of the image Differences in intensity in parts of the image corresponding to different concentrations of corresponding to different concentrations of activity within the patientactivity within the patient

Spatial ResolutionSpatial ResolutionFull Width Half Maximum (FWHM)Full Width Half Maximum (FWHM)

FWHMFWHM

Full Maximum

Half Maximum

Significance of FWHMSignificance of FWHM

FWHM and ResolutionFWHM and Resolution

Two sources separated by the FWHM will Two sources separated by the FWHM will be resolvedbe resolved

Easy to measure using modern processing Easy to measure using modern processing computerscomputers

Typical values:Typical values: LEHR at 0mm; LEHR at 0mm; 4.6mm4.6mm LEHR at 100mm: LEHR at 100mm: 8.3mm8.3mm LEGP at 0mm; LEGP at 0mm; 4.7mm4.7mm LEGP at 100mm; LEGP at 100mm; 10.2mm10.2mm

Image Quality: CollimatorImage Quality: Collimator

High Sensitivity, General Purpose, High High Sensitivity, General Purpose, High ResolutionResolution Trade off between spatial resolution and sensitivityTrade off between spatial resolution and sensitivity

Distance DependenceDistance Dependence

4

6

8

10

12

14

16

18

20

0 50 100 150

Source-Collimator Distance (mm)

FW

HM

(m

m)

0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150

Source-Collimator Distance (mm)

Re

lati

ve

Se

ns

itiv

ity

LEHSLEHS

LEGPLEGP

LEGPLEGP

LEHSLEHS

NoiseNoise

All stages in imaging system subject to All stages in imaging system subject to statistical variationstatistical variation Radioactive decayRadioactive decay Number of scintillation photons in crystalNumber of scintillation photons in crystal Number of electrons at photocathode and Number of electrons at photocathode and

dynodes… dynodes…

SD of Noise = √(Average Pixel Count)SD of Noise = √(Average Pixel Count) More counts = better S/N ratioMore counts = better S/N ratio

NoiseNoise

Avg Pix Avg Pix CountCount

SDSD NoiseNoise

100100 1010 10%10%

10001000 3232 3%3%

10,00010,000 100100 1%1%

Increased Counts Increased Counts → Reduced Noise→ Reduced Noise

Image Quality: Recorded Image Quality: Recorded CountsCounts

Administered ActivityAdministered Activity Diagnostic Reference Levels - ARSACDiagnostic Reference Levels - ARSAC

UptakeUptake Radiopharmaceutical PropertiesRadiopharmaceutical Properties Time to ImagingTime to Imaging

AttenuationAttenuation Patient SizePatient Size

Acquisition TimeAcquisition Time Typical Imaging Times 3-60 minutesTypical Imaging Times 3-60 minutes

ContrastContrast

Contrast = Contrast = (R1 - R2)(R1 - R2)

R2 R2 R2: BackgroundR2: Background

R1: LesionR1: Lesion

Image Quality: Background ActivityImage Quality: Background Activity

Non-specific radiopharmaceutical uptakeNon-specific radiopharmaceutical uptake Choice of pharmaceuticalChoice of pharmaceutical PathologyPathology

ScatterScatter Limited energy resolutionLimited energy resolution

Septal PenetrationSeptal Penetration Photon energyPhoton energy Collimator choiceCollimator choice

Image Quality: Patient MotionImage Quality: Patient Motion

Long Imaging TimesLong Imaging Times Limit to time patient can remain stillLimit to time patient can remain still ~60% of Cardiac scans need correction~60% of Cardiac scans need correction Positioning and immobilisation devices can Positioning and immobilisation devices can

help but still limit to 30minshelp but still limit to 30mins

Physiological MotionPhysiological Motion Cardiac GatingCardiac Gating Respiratory GatingRespiratory Gating

Image Quality ComparisonImage Quality Comparison

Thallium-201 Tc99m-tetrofosmin

MYO97C33 TET97036

SAME PATIENT

Image ArtefactsImage Artefacts

PharmaceuticalPharmaceutical Labelling problemsLabelling problems

PatientPatient AttenuationAttenuation MovementMovement ContaminationContamination

EquipmentEquipment Image non-uniformityImage non-uniformity Centre of Rotation Centre of Rotation

errorserrors

OperatorOperator External attenuationExternal attenuation Acquisition errorsAcquisition errors

The Nuclear Medicine “What…?!” The Nuclear Medicine “What…?!” QuizQuiz

Normal ImagesNormal Images Abnormal images Abnormal images Images with artefacts caused by: Images with artefacts caused by:

Patient movement, Patient movement, Co-morbiditiesCo-morbidities Pharmaceutical problemsPharmaceutical problems ContaminationContamination Incorrect processingIncorrect processing

Can you tell which is which? Can you tell which is which? (Sadly no prize for the winner!)(Sadly no prize for the winner!)

Normal Bone ScanNormal Bone Scan

SymmetrySymmetry

Kidneys and Kidneys and

bladderbladder

Soft TissueSoft Tissue

““Superscan”Superscan”

Axial skeleton and Axial skeleton and pelvis almost pelvis almost complete metastasescomplete metastases

Retains symmetryRetains symmetry Cannot visualise Cannot visualise

urinary systemurinary system Cannot visualise soft Cannot visualise soft

tissuetissue Limb bones poorly Limb bones poorly

visulisedvisulised

ContaminationContamination

Urinary Urinary contamination contamination commoncommon

Often find traces in Often find traces in departmentdepartment

Patient hands?!Patient hands?!

Urinary Catheter Urinary Catheter and Bagand Bag

Extremely common Extremely common in Ca Prostate in Ca Prostate patientspatients

Image with emptied Image with emptied bag moved out of bag moved out of field of viewfield of view

If only find out later, If only find out later, re-image legs re-image legs separatelyseparately

Free Free PertechnetatePertechnetate

Improper labelling Improper labelling of the HDPof the HDP

Can see stomach, Can see stomach,

heart and thyroidheart and thyroid Usually results in Usually results in

increase in doseincrease in dose

A little bit unfair… A little bit unfair…

ExtravasationExtravasation Can obscure joints Can obscure joints Always administer on Always administer on

opposing side to opposing side to suspect jointssuspect joints

Always use a venflon Always use a venflon or butterflyor butterfly

Radiation necrosis in Radiation necrosis in therapy dosestherapy doses

Ventilation scanVentilation scan

Use radioactive Use radioactive aerosol although can aerosol although can use gasses or use gasses or particlesparticles

Normally used with Normally used with perfusion scan for PEperfusion scan for PE

Can be used for Can be used for volume and function volume and function estimationestimation

PE is normally wedge shaped, this is PE is normally wedge shaped, this is roundround

Chest x-rays routinely performed as part of Chest x-rays routinely performed as part of the VQ procedure the VQ procedure

Attenuation

Planar Myocardial Planar Myocardial Perfusion StudyPerfusion Study

Very old study Very old study

Performed with Performed with Tl-201Tl-201

Modern images are Modern images are done as SPECTdone as SPECT

Myocardial Myocardial Perfusion Perfusion StudyStudy

Where is the Where is the heart?heart?

Carefully Carefully examine examine outline of outline of patientpatient

Breast Breast attenuationattenuation

Breast AttenuationBreast Attenuation

Breast Breast AttenuationAttenuation

Classic breast Classic breast

attenuation patternattenuation pattern

““Defects” in antero-Defects” in antero-

septal regionseptal region

Defects are fixedDefects are fixed

Walls move normallyWalls move normally

DMSA Kidney ScanDMSA Kidney Scan

Looks for scarred areas Looks for scarred areas

of kidneysof kidneys

Can be used to Can be used to

determine the divided determine the divided

function of the kidneysfunction of the kidneys

Can be useful post UTICan be useful post UTI

DMSA Scan with DMSA Scan with patient motionpatient motion

Patient has moved Patient has moved position midway through position midway through the scanthe scan

Has effect of smearing Has effect of smearing the counts and making the counts and making the kidney look big and the kidney look big and underperfusedunderperfused

Repeat imaging shows Repeat imaging shows normal perfusionnormal perfusion

ThyroidThyroid

Many Many radiopharmaceuticals radiopharmaceuticals are taken up by are taken up by thyroidthyroid

Thyroid imaging used Thyroid imaging used in parathyroid in parathyroid localisation scanslocalisation scans

Gastric Emptying Gastric Emptying StudyStudy

Used to examine Used to examine gastric emptying gastric emptying problemsproblems

Now also used in Now also used in gastric pacing gastric pacing studiesstudies

DATScanDATScan Binds to pre-synaptic Binds to pre-synaptic

dopamine dopamine transporterstransporters

Diagnosis of Diagnosis of Parkinsonian Parkinsonian disordersdisorders Normal appearance is Normal appearance is

comma shaped comma shaped putamenputamen

Abnormal is “full stop” Abnormal is “full stop” shape of one or both shape of one or both putamenputamen

Normal shaped Putamen Normal shaped Putamen What’s making it look “odd”What’s making it look “odd” Change the windowing of the images…Change the windowing of the images…

““Missing” section of brain?!Missing” section of brain?! Patient brought back for CT scanPatient brought back for CT scan CT showed large arachnoid cystCT showed large arachnoid cyst

Post ablation Post ablation thyroid scanthyroid scan

Taken 7-10 days Taken 7-10 days after ablationafter ablation

Still large amount of Still large amount of I-131 in the patient’s I-131 in the patient’s systemsystem

Star artefact due to Star artefact due to poor windowingpoor windowing hexagonal collimator hexagonal collimator

holesholes High Activity in thyroidHigh Activity in thyroid

Micturating renogramMicturating renogram Kidneys get hotter suggesting refluxKidneys get hotter suggesting reflux But, background changes intensity and analysis But, background changes intensity and analysis

suggests no increase in kidney countssuggests no increase in kidney counts

Incorrect display Incorrect display

LymphoscintigramLymphoscintigram

Administration of Administration of radioactive colloid radioactive colloid

Colloid moved through Colloid moved through the lymphatic system the lymphatic system

Allows assessment of Allows assessment of the cause of the cause of lymphoedemalymphoedema

Radionuclide Radionuclide VentriculogramVentriculogram

Red cells are labelled Red cells are labelled with pertechnetatewith pertechnetate

The image is acquired The image is acquired gatedgated

Allows precise, Allows precise, repeatable repeatable measurement of LVEFmeasurement of LVEF

OesophagogastrectomyOesophagogastrectomy Stomach pulled into thoraxStomach pulled into thorax One minute before the bone scan the patient One minute before the bone scan the patient

drank his radioactive urinedrank his radioactive urine

UriposiaUriposia

Another unfair one…

DMSA kidney images DMSA kidney images with apparent uptake with apparent uptake in the gutin the gut

Originally suspected Originally suspected to be improper to be improper labelling or labelling or contamination of contamination of pharmaceutical pharmaceutical

Later found to be Later found to be caused by the patient caused by the patient drinking their own drinking their own urineurine

Just shows that Just shows that Uriposia is not Uriposia is not thatthat uncommon…uncommon…