Assessment of myocardial viability with SPECT and PET imaging.

The use of thrombolytic therapy for the treatment of acute myocardial infarction has increased the number of patients presenting for assessment of myocardial viability. Stress SPECT 201Tl perfusion imaging performed in the conventional manner with delayed imaging at 4 hr can identify a large percentage of patients with ischemic but viable areas of myocardium. In some patients, delayed imaging up to as long as 24-48 hr after exercise may be required to show 201Tl redistribution indicative of viability. Thus, in most patients, stress 201Tl scintigraphy will correctly identify the presence of viable myocardium. PET imaging, with its ability to assess blood flow and metabolism separately, offers the ability to identify myocardial areas with diminished blood flow but preserved metabolism. Areas with such a blood flow-metabolism mismatch may benefit from revascularization, even in the absence of 201Tl redistribution. The exact role PET will play in the initial evaluation of patients presenting for assessment of myocardial viability remains to be established as more clinical data are accumulated.