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Attenuation Artifacts Thomas H. Hauser, MD, MMSc Director of Nuclear Cardiology Beth Israel Deaconess Medical Center Instructor in Medicine Harvard Medical.

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Presentation on theme: "Attenuation Artifacts Thomas H. Hauser, MD, MMSc Director of Nuclear Cardiology Beth Israel Deaconess Medical Center Instructor in Medicine Harvard Medical."— Presentation transcript:

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

2 Harvard Medical School THH 10/04 Cases Prone imaging Stress: 99m Tc-Sestamibi Rest: 201 Tl

3 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Case 1

5 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Case 2

7 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Attenuation

9 Harvard Medical School THH 10/04 Low Photon Counts

10 Harvard Medical School THH 10/04 People are not Uniform

11 Harvard Medical School THH 10/04 People are not Uniform

12 Harvard Medical School THH 10/04 Outline Typical patterns of attenuation artifacts Supine/Prone Imaging Gated Imaging Attenuation Correction

13 Harvard Medical School THH 10/04 Outline Typical patterns of attenuation artifacts Supine/Prone Imaging Gated Imaging Attenuation Correction

14 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Inferior Attenuation

16 Harvard Medical School THH 10/04 Anterior Attenuation

17 Harvard Medical School THH 10/04 Anterior Attenuation

18 Harvard Medical School THH 10/04 Arm Attenuation

19 Harvard Medical School THH 10/04 Arm Attenuation

20 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Outline Typical patterns of attenuation artifacts Supine/Prone Imaging Gated Imaging Attenuation Correction

22 Harvard Medical School THH 10/04 Supine/Prone Imaging

23 Harvard Medical School THH 10/04 Positional Imaging Supine Imaging –Inferior attenuation increased –Anterior attenuation decreased Prone Imaging –Anterior attenuation increased –Inferior attenuation decreased

24 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Supine Prone Imaging Pros –Cheap –Easy Cons –Little data –Relatively poor performance

26 Harvard Medical School THH 10/04 Outline Typical patterns of attenuation artifacts Supine/Prone Imaging Gated Imaging Attenuation Correction

27 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Gated Imaging

29 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Gated Imaging

31 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Gated Imaging

34 Harvard Medical School THH 10/04 Correlation of SPECT and MR EDV Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

35 Harvard Medical School THH 10/04 Correlation of SPECT and MR EF Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

36 Harvard Medical School THH 10/04 Differences between SPECT and MR EF Ioannidis et al, J Am Coll Cardiol 2002;39:2059–68

37 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Arrhythmia

39 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Arrhythmia Rejection

41 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Atrial Fibrillation

43 Harvard Medical School THH 10/04 Gating Error due to AF

44 Harvard Medical School THH 10/04 Severe Defect

45 Harvard Medical School THH 10/04 Small Heart

46 Harvard Medical School THH 10/04 Small Heart

47 Harvard Medical School THH 10/04 Small Heart

48 Harvard Medical School THH 10/04 Gated Imaging and Attenuation Gated images provide functional data about regional systolic function –Translation –Wall thickening

49 Harvard Medical School THH 10/04 Inferior Attenuation

50 Harvard Medical School THH 10/04 Inferior Attenuation

51 Harvard Medical School THH 10/04 Patients WITHOUT CAD Smanio et al, J Am Coll Cardiol 1997;30:1687–92

52 Harvard Medical School THH 10/04 Patients WITH CAD Smanio et al, J Am Coll Cardiol 1997;30:1687–92

53 Harvard Medical School THH 10/04 Change in Interpretation Smanio et al, J Am Coll Cardiol 1997;30:1687–92

54 Harvard Medical School THH 10/04 Outline Typical patterns of attenuation artifacts Supine/Prone Imaging Gated Imaging Attenuation Correction

55 Harvard Medical School THH 10/04 Attenuation Map

56 Harvard Medical School THH 10/04 Attenuation Map

57 Harvard Medical School THH 10/04 Algorithmic Reconstruction

58 Harvard Medical School THH 10/04 Truncation

59 Harvard Medical School THH 10/04 Attenuation Correction

60 Harvard Medical School THH 10/04 Attenuation Correction

61 Harvard Medical School THH 10/04 Attenuation Correction

62 Harvard Medical School THH 10/04 Attenuation Correction: Sensitivity for Detection of >50% Stenosis

63 Harvard Medical School THH 10/04 Attenuation Correction: Reader Confidence

64 Harvard Medical School THH 10/04 Attenuation Correction

65 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Attenuation Correction Links et al. J Nucl Cardiol 2002;9:183–7

67 Harvard Medical School THH 10/04 Attenuation Correction Links et al. J Nucl Cardiol 2002;9:183–7

68 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

70 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

71 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

72 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

73 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

74 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

75 Harvard Medical School THH 10/04 Attenuation Correction O’Connor et al. J Nucl Cardiol 2002;9:361–76

76 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Case 1: Projection Data

81 Harvard Medical School THH 10/04 Case 1: Attenuation Map

82 Harvard Medical School THH 10/04 Case 1: Filtered Backprojection

83 Harvard Medical School THH 10/04 Case 1: Attenuation Correction

84 Harvard Medical School THH 10/04 Case 1: Gated Images

85 Harvard Medical School THH 10/04 Case 1: Diaphragmatic Attenuation Mild intensity Fixed Inferior wall Graded appearance Resolves with attenuation correction Normal wall motion

86 Harvard Medical School THH 10/04 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 Harvard Medical School THH 10/04 Case 2: Projection Data

88 Harvard Medical School THH 10/04 Case 2: Attenuation Map

89 Harvard Medical School THH 10/04 Case 2: Filtered Backprojection

90 Harvard Medical School THH 10/04 Case 2: Attenuation Correction

91 Harvard Medical School THH 10/04 Case 2: Gated Images

92 Harvard Medical School THH 10/04 Case 2: Breast Attenuation Moderate intensity Fixed Anterior wall, with relative sparing of the apex Resolves with attenuation correction Normal wall motion

93 Harvard Medical School THH 10/04 Case 3

94 Harvard Medical School THH 10/04 Inferior Ischemia

95 Harvard Medical School THH 10/04 Case 4

96 Harvard Medical School THH 10/04 Multivessel Disease

97 Harvard Medical School THH 10/04 Case 5

98 Harvard Medical School THH 10/04 Case 5: Attenuation Correction

99 Harvard Medical School THH 10/04 Case 5: Gated Images

100 Harvard Medical School THH 10/04 Case 5 Inferior Infarction Mild defect Distribution typical for CAD Persists after attenuation correction Distal inferior hypokinesis

101 Harvard Medical School THH 10/04 Case 6

102 Harvard Medical School THH 10/04 Case 6: Attenuation Correction

103 Harvard Medical School THH 10/04 Case 6: Gated Images

104 Harvard Medical School THH 10/04 Case 6 Anterior Infarction Severe defect Distribution typical for attenuation Persists with attenuation correction Anterior hypokinesis


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