Myocardial Perfusion Imaging
Use of myocardial perfusion imaging (MPI or MPS) is preferable to “stress nuclear imaging,” but both terms are used interchangeably. In general, images at peak stress and at rest reflect changes in the distribution of the radiopharmaceutical if ischemia is present (see Plate 3-16; SPECT, single-photon emission tomography). Indications for MPI are as follows :
1. To detect and provide semiquantitative information about
ischemia, especially when the ECG may not be useful during exercise (e.g.,
patients with left bundle branch block).
2. To distinguish a false-positive ECG response for patients
who are asymptomatic during exercise but have striking ECG alteration (e.g., ST
segment depression); normal radionuclide uptake in these patients is highly
suggestive of a false-positive ECG response to exercise.
3. To assess previous or new myocardial infarction and to
provide some semiquantitative information about the size of the infarction.
4. To provide information on the functional significance of
a specific coronary artery stenosis found at angiography(e.g., patient with
50%-60% stenosis of left anterior descending coronary artery and 90% stenosis
of a right coronary artery has exercise radionuclide test to detect regional
abnormality in distribution of descending as well as right coronary artery).
Unfortunately,
a false-positive test for “ischemia” can occur, especially in patients who have
any type of infiltrative disease within the myocardium, such as myocarditis or
tumors. False-negative results are also found, especially when the ischemic
area of the myocardium is too small to be detected by this technique.
