The thallium washout was analyzed in 40 patients with angiographically documented CAD, using circumferential time-activity profiles of the initial and four-hour delayed images. A net washout pattern (fewer counts in delayed images than initial images) was observed in the distribution of normal and diseased vessels. A negative washout (washin)(a net increase in counts in the four-hour delayed images) was observed only in the presence of diseased vessels, even if the initial scans were normal. Quantitative analysis of thallium kinetics was shown to be important in rest images, and should be performed event if the initial images appear normal.
