1. Attenuation Artifacts
A major teaching hospital of Harvard Medical School
Attenuation Artifacts
Thomas H. Hauser, MD, MMSc
Director of Nuclear Cardiology
Beth Israel Deaconess Medical Center
Instructor in Medicine
Harvard Medical School
Boston, MA

2. Cases
Prone imaging
Stress: 99mTc-Sestamibi
Rest: 201Tl

3. Case 1
65 year-old man with a history of HTN who presented with chest pain. He was referred for an exercise stress test with nuclear imaging
He exercised for 6.5 minutes of a Bruce protocol
Peak HR 143 (92% predicted maximal)
Peak BP 194/64
During exercise, he had chest pain but no ECG changes

4. Case 1

5. Case 2
82 year-old woman with a history of CAD, s/p multi-vessel PCI, HTN, dyslipidemia who presented with chest pain. She was referred for dipyridamole stress with nuclear imaging.
Appropriate hemodynamic response with a fall in BP and an increase in HR.
She had no symptoms or ECG changes.

6. Case 2

7. Challenge of Fixed Defects
Fixed defects can represent either myocardial infarction or an artifact due to soft tissue attenuation
Difficult to distinguish between them using standard filtered backprojection images alone
Soft tissue attenuation is very common
Major limitation in the specificity of SPECT imaging for the detection of CAD

8. Attenuation

9. Low Photon Counts

10. People are not Uniform

11. People are not Uniform

12. Outline Typical patterns of attenuation artifacts Supine/Prone Imaging
Gated Imaging
Attenuation Correction

13. Outline Typical patterns of attenuation artifacts Supine/Prone Imaging
Gated Imaging
Attenuation Correction

14. Attenuation Artifact Patterns
Inferior (“Diaphragmatic”) Attenuation
Related to weight/abdominal girth
Inferior wall
Worse near the base
Anterior (Breast) Attenuation
Anterior wall
Usually sparing the apex
Arm Attenuation
Arms down imaging
Anteroseptal and inferolateral walls

15. Inferior Attenuation

16. Anterior Attenuation

17. Anterior Attenuation

18. Arm Attenuation

19. Arm Attenuation

20. Characteristics of Attenuation Artifacts
Tend to be of mild intensity, but can be moderate
Usually follow one of these typical patterns
Usually evidence of attenuation on the projection images or the attenuation map

21. Outline Typical patterns of attenuation artifacts Supine/Prone Imaging
Gated Imaging
Attenuation Correction

22. Supine/Prone Imaging
                              

23. Positional Imaging Supine Imaging Prone Imaging
Inferior attenuation increased
Anterior attenuation decreased
Prone Imaging
Anterior attenuation increased
Inferior attenuation decreased

24. Supine/Prone Imaging
True perfusion defects are independent of position
Attenuation artifacts often change depending on patient position
If a defect appears or disappears with a change in position, then it is an artifact
Segall et al. J Nucl Med 1989;30:

25. Supine Prone Imaging Pros Cons Cheap Easy Little data
Relatively poor performance

26. Outline Typical patterns of attenuation artifacts Supine/Prone Imaging
Gated Imaging
Attenuation Correction

27. Gated Imaging Divides the cardiac cycle into phases
Data collected during each phase is pooled to form a single image
Images from each phase are put together to compose a series of images called a cine
Further information can then be obtained from this data by applying computer algorithms.

28. Gated Imaging

29. Gated Images
The number of gates depends on the desired temporal resolution and image quality
Always a trade-off between them
Finite number of counts
8, 16, 32, 64
Traditional vs. List mode
List mode not frequently used
Fixed vs. Variable RR interval

30. Gated Imaging

31. Gated Imaging
Although the display used at BIDMC shows four slices, the gated cine images are 3D.
Any set of slices can be selected
Many systems show the 3D images

32. Quantification
3D images allow for accurate quantification of volumes in each phase of the cardiac cycle
Calculated by using computerized edge detection to determine the endocardial border
Usually displayed as a time-volume curve
LVEF = 1-(ESV/EDV)

33. Gated Imaging

34. Correlation of SPECT and MR EDV
Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

35. Correlation of SPECT and MR EF
Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

36. Differences between SPECT and MR EF
Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

37. Image Quality
To get accurate quantification, the computer must be able to accurately detect the endocardium
Regular rhythm
Motion or other artifacts that significantly affect the perfusion images
Severe defects (real or attenuation)
No counts, no border
Small hearts

38. Arrhythmia

39. Arrhythmia If the R wave occurs prior to the expected time
Later phases are empty for the prior beat
Timing of systole is different for next beat
If the R wave occurs after the expected time
Little effect on the prior beat
Timing of systole is different for the next beat
Either causes image blurring
To preserve image quality, RR intervals that deviate from the expected are rejected

40. Arrhythmia Rejection

41. Arrhythmia Many software packages generate a histogram of RR intervals
Helpful to determine presence and severity of arrhythmia
If there is frequent arrhythmia rejection, then acquisition time can be overly prolonged
Use non-gated imaging with severe arrhythmia

42. Atrial Fibrillation

43. Gating Error due to AF

44. Severe Defect

45. Small Heart

46. Small Heart

47. Small Heart

48. Gated Imaging and Attenuation
Gated images provide functional data about regional systolic function
Translation
Wall thickening

49. Inferior Attenuation

50. Inferior Attenuation

51. Patients WITHOUT CAD
Smanio et al, J Am Coll Cardiol 1997;30:1687–92

52. Patients WITH CAD
Smanio et al, J Am Coll Cardiol 1997;30:1687–92

53. Change in Interpretation
Smanio et al, J Am Coll Cardiol 1997;30:1687–92

54. Outline Typical patterns of attenuation artifacts Supine/Prone Imaging
Gated Imaging
Attenuation Correction

55. Attenuation Map

56. Attenuation Map

57. Algorithmic Reconstruction

58. Truncation

59. Attenuation Correction

60. Attenuation Correction

61. Attenuation Correction

62. Attenuation Correction: Sensitivity for Detection of >50% Stenosis

63. Attenuation Correction: Reader Confidence

64. Attenuation Correction

65. Attenuation Correction
Links et al evaluated 66 patients using information from both attenuation corrected images and gated images
Combination of both provided the highest diagnostic accuracy
Links et al. J Nucl Cardiol 2002;9:183–7

66. Attenuation Correction
Links et al. J Nucl Cardiol 2002;9:183–7

67. Attenuation Correction
Links et al. J Nucl Cardiol 2002;9:183–7

68. Attenuation Correction
O’Connor et al evaluated the performance of all available SPECT systems with attenuation correction.
Highly variable results depending on the system
Inability to reproduce normal phantom images in the presence of attenuation
Inability to consistently depict inferior or anterior defects
Significant artifacts in the presence of adjacent hot spots
O’Connor et al. J Nucl Cardiol 2002;9:361–76

69. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

70. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

71. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

72. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

73. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

74. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

75. Attenuation Correction
O’Connor et al. J Nucl Cardiol 2002;9:361–76

76. ASNC/SNM Statement
“It is the position of ASNC and the SNM that incorporation of attenuation correction in addition to ECG gating with SPECT myocardial perfusion images will improve image quality, interpretive certainty, and diagnostic accuracy. These combined results are anticipated to have a substantial impact on improving the effectiveness of care and lowering health care costs.”
Heller et al. J Nucl Cardiol. 2004;11:229

77. ASNC/SNM Statement
High-quality transmission scans and sufficient transmission counts with low cross-talk from the emission radionuclide are essential to reduce the propagation of noise and error into the corrected emission images.
Quality-control procedures for image registration should be used for projection data acquired by use of sequential transmission-emission imaging protocols (eg, computed tomography–SPECT systems).
Motion correction, scatter correction, and resolution recovery should be used with attenuation correction.
Attenuation correction should be employed concurrently with ECG-gated SPECT imaging.
Technologists must have adequate training in the acquisition and processing of attenuation-corrected studies. Physicians must have adequate training in the interpretation of attenuation-corrected images.
Physicians should view and interpret both uncorrected and corrected images.
Heller et al. J Nucl Cardiol. 2004;11:229

78. An Integrative Approach to Recognizing Attenuation Artifacts
Inspect the raw data for evidence of attenuation
Projection images: visualize attenuation
Attenuation map: attenuating structures
Recognize the typical patterns of attenuation artifacts
If available, compare supine/prone images
Examine attenuation corrected images
Examine the gated images

79. Case 1
65 year-old man with a history of HTN who presented with chest pain. He was referred for an exercise stress test with nuclear imaging
He exercised for 6.5 minutes of a Bruce protocol
Peak HR 143 (92% predicted maximal)
Peak BP 194/64
During exercise, he had chest pain but no ECG changes

80. Case 1: Projection Data

81. Case 1: Attenuation Map

82. Case 1: Filtered Backprojection

83. Case 1: Attenuation Correction

84. Case 1: Gated Images

85. Case 1: Diaphragmatic Attenuation
Mild intensity
Fixed
Inferior wall
Graded appearance
Resolves with attenuation correction
Normal wall motion

86. Case 2
82 year-old woman with a history of CAD, s/p multi-vessel PCI, HTN, dyslipidemia who presented with chest pain. She was referred for dipyridamole stress with nuclear imaging.
Appropriate hemodynamic response with a fall in BP and an increase in HR.
She had no symptoms or ECG changes.

87. Case 2: Projection Data

88. Case 2: Attenuation Map

89. Case 2: Filtered Backprojection

90. Case 2: Attenuation Correction

91. Case 2: Gated Images

92. Case 2: Breast Attenuation
Moderate intensity
Fixed
Anterior wall, with relative sparing of the apex
Resolves with attenuation correction
Normal wall motion

93. Case 3

94. Inferior Ischemia

95. Case 4

96. Multivessel Disease

97. Case 5

98. Case 5: Attenuation Correction

99. Case 5: Gated Images

100. Case 5 Inferior Infarction Mild defect Distribution typical for CAD
Persists after attenuation correction
Distal inferior hypokinesis

101. Case 6

102. Case 6: Attenuation Correction

103. Case 6: Gated Images

104. Case 6 Anterior Infarction Severe defect
Distribution typical for attenuation
Persists with attenuation correction
Anterior hypokinesis