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…