1. Myocardial Perfusion Imaging Atomic Energy Medical Centre, JPMC.
Image Artifacts
and
Pitfalls
Dr. Hasan Raza
Atomic Energy Medical Centre, JPMC.

2. Image Artifacts and Pitfalls
MPI is a valuable diagnostic tool
It is also a complex physiologic imaging process, which exposes it to several potential pitfalls and artifacts that can limit the utility of the study.

3. Image Artifacts and Pitfalls
Technical
Sources of
Error
Patient Related
Issues .
Patient Motion
LBBB
Attenuation
Hypertrophic cardiomyopathy
Reconstruction Artifacts
Balanced Ischemia
Myocardial Statistics

4. Evaluation of the Images for Technical Sources of Error
Patient Motion
Attenuation
Reconstruction Artifacts
Myocardial Statistics.
...

5. Evaluation of the Images for Technical Sources of Error
Patient Motion
Attenuation
Reconstruction Artifacts
Myocardial Statistics.
...

6. Patient Motion
Patient motion is a common source of artifact on MPI studies.
The greater the extent of movement, the greater is the likelihood of artifact.
Images should be inspected for the presence of patient motion
A cine display of the planar projection data is highly recommended
A static “sinogram” may be used to detect motion

7. Patient Motion
Movement of 2 or more pixels always caused a detectable artifact
Generally up and down motion is less deleterious to image quality than sideways motion.
Motion occurring in the middle of the acquisition is more significant than motion near the beginning or the end
Abrupt patient motion is more significant than gradual motion
Software routines are available for correction of motion.
...

8. Patient Motion
The raw data viewed in cine mode demonstrated significant patient motion in 2 raw data frames. On the resultant images, there is an artifactual perfusion defect in the apical septum

9. Evaluation of the Images for Technical Sources of Error
Patient Motion
Attenuation
Reconstruction Artifacts
Myocardial Statistics.
...

10. Attenuation
Attenuation of photons by the patient’s body is responsible for one of the most prevalent artifacts in MPI.
A large body habitus results in generalized decreased counts
Focal attenuation is typically due to breasts in women and
the diaphragm in men
...

11. Breast Attenuation
Breast attenuation usually results in a perfusion defect along the anterior wall of the LV, although, depending on body habitus, the lateral wall, septum, and even the apex can be affected
A fixed defect along with normal motion and thickening on the gated study does favor breast attenuation
The raw data in cine format should be evaluated to appreciate the size and density of the breasts
Breast attenuation can sometimes be improved by repeating the acquisition with the breast repositioned.

12. Breast Attenuation
Myocardial perfusion scan reveals a fixed defect in the anterior wall (arrowheads).
Frame from raw data demonstrates marked attenuation by left breast (arrowheads), which is causing the apparent perfusion defect.

13. Breast Attenuation Myocardial perfusion
scan reveals a reversible defect in anterior
wall (arrowheads).
Breast Attenuation??
Breast positioning should be similar on the stress
and rest images to optimize accurate interpretation

14. Diaphragmatic Attenuation
Large abdomens due to diaphragm result in attenuation of the inferior wall.
This is more commonly seen in men, resulting in sex differences. In typical myocardial perfusion patterns, with men often having a mild artifactual defect in the inferior wall
Diaphragmatic attenuation may be minimized by imaging the patient prone.

15. Diaphragmatic Attenuation
A) Myocardial perfusion scan demonstrates typical mild fixed inferior wall perfusion abnormality (arrowheads) in male patient resulting from diaphragmatic attenuation.
B) Quantitative analysis using appropriate male database indicates no significant abnormality
C) When incorrectly reprocessed comparing with female normal database, this male patient appears to have a significant fixed defect in inferior wall

16. Evaluation of the Images for Technical Sources of Error
Patient Motion
Attenuation
Reconstruction Artifacts
Myocardial Statistics.
...

17. Reconstruction Artifacts
Adjacent extracardiac activity may also affect the reconstructed myocardial images
Superimposed bowel loops or liver activity may create artifactually intense uptake in the overlapped myocardium that could mask a real perfusion defect
Intense activity in bowel loops or adjacent liver may cause a negative reconstruction artifact, resulting in an apparent reduction in activity in the adjacent myocardial segments.

18. Reconstruction Artifacts
There is currently no reliable correction for such artifacts
They may be less prominent with iterative as opposed to filtered back-projection techniques
They can often be eliminated by repeating the acquisition after the activity level in the adjacent structure has decreased.

19. Reconstruction Artifacts
Due to prominent liver activity adjacent to inferior wall defect on rest images, it impossible to tell if there is any
reversibility present.

20. Reconstruction Artifacts
Rest study was repeated with longer delay between injection and imaging, resulting in no confounding liver
activity and, thus, a diagnostic scan.

21. Reconstruction Artifacts
Perfusion images demonstrate apparent perfusion defect in inferior wall that is much worse at rest than during
stress (arrowheads).
Anterior frames from raw data reveal liver activity to be much greater than cardiac activity at rest (left frame), which is not the case on the stress study

22. Evaluation of the Images for Technical Sources of Error
Patient Motion
Attenuation
Reconstruction Artifacts
Myocardial Statistics
...

23. Myocardial Statistics
Perfusion defects can be artifactually created simply because of poor statistics
Many factors are involved in the final count density of perfusion images including
Body habitus
Exercise level
Radiopharmaceutical dose
Acquisition time
Energy window
Collimation
...

24. Myocardial Statistics
Count density in the planar projection images should be noted because the quality of the reconstructed data is a direct reflection of the raw data
As a general rule, peak pixel activity in the left ventricular myocardium in an anterior planar projection should exceed 100 counts for a Tl-201 study and 200 counts in a Tc-99m study
...

25. Myocardial Statistics
Raw data images demonstrate low counts in stress image, similar to low dose rest image, resulting from an infiltrated injection during stress study (B).
Raw data from a repeat-stress study (right panel) on the following day demonstrate expected better counts from high-dose stress study
Repeat-stress study demonstrates a stress-induced defect in anteroseptum (arrowheads) not present on the study with infiltrated injection.
...

26. Patient related Issues
LBBB
Hypertrophic cardiomyopathy
Balanced Ischemia
...

27. Patient related Issues
LBBB
Hypertrophic cardiomyopathy
Balanced Ischemia
...

28. Left Bundle Branch Block (LBBB)
LBBB is a conduction abnormality in which the signal cannot pass through the left bundle branch
In this situation conduction to the LV comes from the right ventricle and is delayed.
This results in paradoxical septal motion
It can result in a septal defect on perfusion imaging, which may be mistaken for myocardial infarction or ischemia

29. Left Bundle Branch Block (LBBB)
Mechanism for the apparent defect has not been completely
established but likely results from compromise of diastolic
blood flow due to the delayed septal contraction
This compromise is accentuated by increasing heart rate
It is less common when using vasodilator stress with
dipyridamole or adenosine than with exercise stress

30. Left Bundle Branch Block (LBBB)
Myocardial perfusion
scan obatined after injection of tracer during chest pain shows septal defect
Patient’s ECG reveals
presence of LBBB.
Patient’s coronary angiogram reveals normal vessels supplying the
septum, including left anterior descending artery (arrows) and septal perforators

31. Patient related Issues
LBBB
Hypertrophic cardiomyopathy
Balanced Ischemia
...

32. Hypertrophic cardiomyopathy
Cardiomyopathies are a group of diseases in which the primary abnormality directly involves the heart muscle
In hypertrophic cardiomyopathy, there is thickening of the myocardium, often particularly involving the septum
This can result in significant increased activity in the septum, which results in the activity in the other walls appearing decreased
This may lead to the erroneous diagnosis of widespread perfusion abnormalities
This phenomenon can also be seen in the setting of hypertension,

33. Hypertrophic cardiomyopathy
Myocardial perfusion scan in patient with hypertrophic cardiomyopathy.
There is marked increased uptake in septum (arrowheads), which leads to the erroneous appearance of decreased perfusion to remaining walls
Major Limitation of MPI
It can only measure relative uptake, not absolute activity

34. Patient related Issues
LBBB
Hypertrophic cardiomyopathy
Balanced Ischemia
...

35. Balanced Ischemia
This limitation of MPI is responsible for another potential pitfall, under recognition of multivessel disease
If there is decreased perfusion to all walls,
particularly if the decrease is of a similar magnitude then this condition is called as ‘‘balanced ischemia’’
The sensitivity for identifying multivessel disease in patients with 3-vessel disease is only approximately 60%

36. Balanced Ischemia
Myocardial perfusion scan reveals inferior and inferolateral defect (arrowheads) with only mild reversibility.
However,patient had critical 3-vessel disease not evident on myocardial perfusion scan, likely a result of ‘‘balanced ischemia’’.

37. Myocardial perfusion
scan reveals a fixed defect.
Lateral wall infarct?
Attenuation?
Or something else?
Situs inversus

38. Conclusion
There are several artifacts and interpretation pitfalls that can potentially compromise MPI
It is essential for both the technologist and the interpreting physician to be aware of these potential sources of error
Appropriate steps should be taken to limit these pitfalls beforehand, where possible correct them if they do occur
When they cannot be eliminated, recognize their potential impact on the interpretation of the study in the final report.

39. Thanks for the Patience