Effects of exercise-induced alterations of cardiac physiology on nuclear perfusion imaging.

The effects produced on nuclear perfusion images by exercise-induced changes in the heart and respiration rate and possible transient myocardial stunning are not well understood. In this study we attempted to indirectly evaluate the potential artifacts created by exercise-induced changes in cardiac physiology. Twenty patients with prior myocardial infarction and suspected peri-infarct ischemia were studied by 99mTc-MIBI imaging. Two SPECT perfusion studies were performed after 99mTc-MIBI administration at rest. The first acquisition was carried out 90 minutes after injection of the tracer. Immediately afterwards, the patients underwent a stress test followed by a second acquisition (exercise stress superimposed on rest tracer distribution). A standard stress perfusion scan was also performed 48 hours later. Superimposed exercise stress produced artifactual defects in the resting distribution of the tracer in 15 out of 20 patients (68 of 360 segments). Standard stress images demonstrated concordant defects in 48 of these segments, indicating the concomitant presence of ischemia and stunning. This study indicates that exercise-induced changes in cardiac physiology may result in artifactual perfusion defects in scintigraphic images acquired shortly after the stress.

Regional cerebral blood flow study with 99mTc-hexamethyl-propyleneamine oxime single photon emission computed tomography in Alzheimer's and multi-infarct dementia.

Thirty-four demented patients, 19 with Alzheimer's and 15 with multi-infarct dementia, were studied using single photon emission computed tomography, and 99mTc-hexamethyl-propylenemine oxime as a tracer of regional cerebral perfusion. Tracer activity ratios, determined in cortical and subcortical regions, were compared with those of 11 age-matched controls. In both groups of demented patients, most of the cortical regions showed significant declines in tracer uptake from control values, with the greatest reductions in the parietal cortex. Significantly lower parietal indexes were found in the Alzheimer's patient group as compared both to the control values and to the group of multi-infarct dementia patients. A positive correlation was found between the magnitude of the parietal deficits and the severity of dementia.