Cardiac Case Study

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Cardiac Case Study

• Inferior wall attenuation and correction with
  CT-based Attenuation Correction

Linda Campbell, BS GE Applications Scientist
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Patient History
A 68 year old male was referred for myocardial
perfusion imaging three months status post
revascularization of the right coronary artery
for evaluation of patency. Some atypical chest
pain was noted.

• Imaging Procedure

The one day Sestamibi protocol was used, and rest
imaging was performed first. SPECT imaging was
done with 60 stops over 180 degrees. In addition,
CT images were acquired. Acquisitions were done
on a GE Hawkeye.
 
Target heart rate (85 of maximum heartrate) 129
Maximal heart rate achieved on treadmill
90
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Imaging Analysis

• As part of the acquisition quality control for
  this data, fused SPECT-CT images were checked for
  proper registration of attenuation maps and
  emission data.

SPECT-CT sagittal fusion
SPECT-CT transaxial fusion
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• Further quality control checks showed the
  acquisition to be of good quality
• The stress and rest selective linograms showed no
  significant motion in the vertical direction and
  showed no significant extra-cardiac activity that
  would interfere with the reconstruction.
• The stress and rest sinograms showed no
  significant motion in the horizontal direction
• Myocardial count density was adequate. The stress
  maximum pixel value was 201 rest maximal pixel
  value was 65. The guideline for an adequate count
  study for 60-64 projection images is to have a
  maximum pixel value of at least 50 counts within
  a tight circular/ elliptical ROI around the
  epicardial edge of the myocardium on an anterior
  view of the heart.
• There were no gating errors

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Question 1 Acquisition quality controlWhich
one of the following acquisition factors has the
least effect on slice image quality? A.
Horizontal motion B. Myocardial count
density C. Gating errors D. Vertical motion E.
Intense extra-cardiac activity adjacent to the
heart
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The correct answer is C - Gating errors

• Thickening is the parameter most prone to error
  in the presence of arrhythmias. Slice appearance
  is maintained in the presence of arrhythmias
  except in very severe cases. LV ejection fraction
  (EF) is a robust parameter that is little
  affected by arrhythmias. Quantitative perfusion
  measures were also little affected by arrhythmias
  except in the case of atrial fibrillation.1

As has been well documented in the literature,
vertical and horizontal motion and myocardial
count density are critical for slice image
quality. Intense visceral activity close to the
heart can also affect slice image quality as it
results in changed slice count densities.
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• The rotating projection images show soft
  tissue attenuation in the waist area which can
  cause increased attenuation of the inferior wall.
  

Click
Click
Stress projection images
Rest projection images
Soft tissue attenuation may create artifacts that
mimic true perfusion abnormalities and can lead
to false positive interpretation.
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Question 2 Attenuation correction

• What are the advantages of doing attenuation
  correction on cardiac studies?
• Provide images that are more uniform and easier
  to interpret
• Decrease acquisition time
• Increase myocardial count density
• Increase sensitivity and overall diagnostic
  accuracy
• Both A and D

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The correct answer is E Both A and D
Attenuation correction can provide images that
are more uniform and easier to interpret, and
increase sensitivity and overall diagnostic
accuracy.
The diagnostic accuracy of SPECT imaging is
compromised by soft tissue attenuation artifacts.
Though education, experience, and the application
of gated SPECT imaging have greatly helped, there
is a need for improved diagnostic accuracy.

Attenuation correction SPECT techniques represent
a significant advance in myocardial perfusion
imaging and hold great promise for improved
assessment of cardiac patients.2
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Question 3 CT-based attenuation correction

• What are the further advantages of doing CT-based
  attenuation correction on cardiac studies?
• A. CT-based AC produces high quality
  transmission maps
• B. CT-based AC is consistent with time
• C. CT-based AC is consistent over a full range
  of body types
• D. All of the above

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The correct answer is D all of the above

• There are significant differences in the ability
  of different commercial AC systems to reduce
  artifacts due to attenuation, hot liver / bowel
  activity and type of orbit. Systems that can
  generate high quality attenuation maps yielded
  the best results. A high quality attenuation map
  appears to be an important determinant of image
  quality.3

Stress attenuation map
Rest attenuation map
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• Stress and rest images were reconstructed by
  filtered back projection (FBP) and iterative
  reconstruction with attenuation correction
  (IR-AC). Count deficiencies in the inferior
  walls of both the stress and rest FBP slices have
  been noticeably improved in the IR-AC slices,
  correcting for inferior wall attenuation.

FBP IR-AC
Stress SA slices
Rest SA slices
FBP IR-AC
Stress VLA slices
Rest VLA slices
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EKG Results
Non-specific ECG changes were noted with no ST
depression at maximal exertion. Test terminated
at maximal heart rate and SOB. No chest pain was
noted.
Findings
FBP images were interpreted as inferior wall scar
with possible ischemic component. This could also
be a diaphragmatic attenuation artifact. With
CT-based AC the inferior wall is shown to be
viable with no ischemia. The validity of the
revascularization of the RCA is confirmed.
For more information on GE Nuclear Cardiology
products and the unique Hawkeye CT based cardiac
AC, visit GE Hawkeye Cardiac Attenuation
Correction
Findings and Images Courtesy of VA Medical
Center, Baltimore, Maryland
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References

• 1. Nichols K, Yao S, Kamran M, Faber TL, Cooke,
  CD, and DePuey EG. Clinical impact of arrhythmias
  on gated SPECT cardiac myocardial perfusion and
  function assessment. J Nucl Cardiol 2001
  819-30.
• 2. Hendel RC, Corbett JR, Cullom SJ, DePuey EG,
  Garcia EV, and Bateman TM. The Value and Practice
  of Attenuation Correction for Myocardial
  Perfusion SPECT Imaging A Joint Position
  Statement form the American Society of Nuclear
  Cardiology and the Society of Nuclear Medicine. J
  Nucl Med 2002 43273-280
• 3. OConnor MK, Kemp B, Anstett F, Christian P,
  Ficaro EP, Frey E, Jacobs M, Kritzman JN,
  Pooley RA, and Wilk M . A multicenter evaluation
  of commercial attenuation compensation techniques
  in cardiac SPECT using phantom models. J Nucl
  Cardiol 2002 9361-76.