Editorial point of viewAttenuation artifact, attenuation correction, and the future of myocardial perfusion SPECT
Section snippets
Prone imaging
Diaphragmatic attenuation of the inferior wall on MPI in the supine position results in false-positive reversible and fixed defects.5 The use of prone imaging has been proposed to improve inferior wall uniformity with both Tl-201 and technetium 99m SPECT imaging. In theory, the heart shifts slightly upward in the prone position, whereas the diaphragm is pushed down, thus increasing the distance between the diaphragm and the inferior wall of the left ventricle and decreasing the potential for
ECG-gated SPECT imaging
ECG-gated functional data may be obtained simultaneously with SPECT MPI. Gating may help in differentiating between CAD and attenuation artifact in patients with fixed perfusion abnormalities. Normal function associated with a fixed defect on perfusion imaging can be classified as a soft-tissue attenuation artifact, whereas abnormal function in conjunction with a similar fixed defect would be compatible with myocardial infarction or myocardial stunning. Gated SPECT imaging cannot be used to
Attenuation correction
Although prone imaging and ECG-gated SPECT imaging have been partially successful in improving identification of attenuation artifact, each has serious limitations. A more scientific approach should use various techniques of attenuation correction, such as routinely performed with positron emission tomography (PET) imaging.20 To apply the methods of attenuation correction, it is necessary to create patient-specific nonuniform attenuation maps that accurately reflect the attenuation potential of
Attenuation correction and the future of myocardial perfusion SPECT
The recently published perspectives on attenuation correction of myocardial perfusion SPECT scans nicely lay out both the intellectualism of our pioneers and the immense dilemma currently confronting our field.4, 55 The past 20 years have seen a virtual explosion in the utilization of myocardial perfusion SPECT imaging, to a point where this technique now accounts for the largest outlay of Medicare dollars going to cardiology services. According to a recent MedPAC analysis, the average annual
Acknowledgment
Authors James A. Case and Timothy M. Bateman receive royalties for ExSPECT II software for myocardial perfusion attenuation correction. Gary V. Heller receives honoraria and unrestricted research grants from Philips Medical Systems.
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