Nuclear Medicine: Nuclear Medicine: Image Quality, Image Quality, Sources of Sources of Artefacts and the Artefacts and the Nuclear Medicine Nuclear Medicine “What… ?!” Quiz “What… ?!” Quiz Katrina Cockburn Katrina Cockburn Nuclear Medicine Nuclear Medicine Physicist Physicist
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Nuclear Medicine: Image Quality, Sources of Artefacts and the Nuclear Medicine “What… ?!” Quiz
Nuclear Medicine: Image Quality, Sources of Artefacts and the Nuclear Medicine “What… ?!” Quiz. Katrina Cockburn Nuclear Medicine Physicist. Image Quality in NM. Image Quality is largely subjective Beware of believing pretty = better! Can measure physical properties: Resolution - PowerPoint PPT Presentation
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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 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
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
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
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
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…