Nuclear Medicine Physics
Image Artifacts in
Nuclear Medicine
Jerry Allison, Ph.D.
Department of Radiology
Medical College of Georgia
Augusta University
A note of thanks to
Z. J. Cao, Ph.D.
Medical College of Georgia
And
Sameer Tipnis, Ph.D.
G. Donald Frey, Ph.D.
Medical University of South Carolina
for
Sharing nuclear medicine presentation content
Artifacts in NM images
 Defects of gamma camera or suboptimal data




acquisition
Photon attenuation
Compensation of photon attenuation in
PET/CT and SPECT/CT
Patient motion
Undesired uptake of radiopharmaceutical
3
Defects of gamma camera
 Defect of collimator or detector
 Bad PMT
 Shift of energy peak out of energy window
 High count rate (> 250,000 counts/sec)
 SPECT artifacts
4
Effect of counts on perceived noise
Image of a brain phantom. As counts
increase, noise decreases.
©1999 by Radiological Society of North America
Rzeszotarski M S Radiographics 1999;19:765-782
Effect of counts on contrast
End –diastole image
©1999 by Radiological Society of North America
Rzeszotarski M S Radiographics 1999;19:765-782
Small dot: collimator defect
7
One PMT  a defective PMT
Multiple PMTs  offset of energy peak
8
Shift of
energy
peak
9
Line: cracked detector
Caused by
mechanical
impact
10
pulse height
High count rate  pile-up
time
11
High count rate
12
COR shift in SPECT
13
Contamination of the
patient's clothing with
radioactivity
14
Myocardial perfusion studies
Attenuation
compensated
vs
Non-compensated
15
Attenuation
by left breast
 an
apparent
defect in the
anterior wall
16
Attenuation by diaphragm  an apparent
defect in the inferior wall
17
Cerebral perfusion studies
Tc-HMPAO or Tc-ECD
Without attenuation correction
Correcteded
18
Misalignment in SPECT/CT
19
Misalignment in SPECT/CT
20
Septal Penetration
Thyroid scan on a patient imaged with
I-131 using a low energy collimator.
Septal Penetration
Ant
Post
These 111In images were obtained simultaneously with a
dual head camera, and the collimator for the posterior
head had not been changed to a medium energy
collimator. Therefore, there is significant septal
penetration (typical star pattern).
2015
Nuclear Medicine Physics for Radiology Residents
Sameer Tipnis, PhD, DABR
A telemetry monitor on patient's chest
23
PET/CT issues
 Attenuation correction
 Resolution
 Metallic artifact
 Truncated CT
 CT contrast
 Respiration misalignment
 Motion
 Brown fat
 Scar
24
Attenuation correction in PET
High uptake
in lungs
Low uptake
in others
High uptake
in skin
w/o
comp
25
2014 PET image of the ACR
phantom
7.9 mm
26
2014 SPECT image of the ACR
phantom
• as
9.5 mm
31.8 mm
15.9 mm
27
Sphere diameters: 9.5, 12.7, 15.9, 19.1, 25.4, and 31.8 mm
Metallic implant
PET comp
PET w/o
CT
28
Truncated CT
PET comp
CT
29
Truncated CT
SUV=1.96
Corrected
SUV=7.44
30
CT contrast
CT
PET comp
PET w/o
31
Respiration misalignment in PET/CT
PET comp
32
Respiration misalignment in PET/CT
PET
comp
PET
w/o
33
Head motion in PET
Corrected
34
Head motion  increased uptake in
right face as compared with the left side
35
Brown fat uptake of 18F-FDG
 keep patient warm
36
Question
PET comp
Pace maker
PET w/o
CT
37
Question
CT truncation
SUV=0.32
Corrected SUV=0.79
38
Question
PET comp
Metallic implant
PET w/o
CT
39
Question
Scar uptake of 18F-FDG
PET comp
40
Time of flight PET image of a
big patient
Why better
resolution?
Less noise 
lighter filtering 
more resolution
preserved
(electronic
collimation)