COMPARISON BETWEEN REFERENCE VALUES FOR TL-201 UPTAKE AND WASHOUT FROM THE MYOCARDIUM AFTER EXERCISE AND AFTER DIPYRIDAMOLE

A slow washout of Thallium-201 has a high diagnostic and prognostic va lue for coronary artery disease. The aim of the present work was to co ntribute with reference data on Tl-201 uptake and washout from the myo cardium. With a quantitative method using circumferential profiles and interpolative background subtraction we performed Tl-201 myocardial i maging in two groups of subjects with a low probability of coronary ar tery disease. Washout in per cent is defined as (1-D/I).100. where D i s the delayed uptake rate and I the initial uptake rate. In group A (n =16) myocardial hyperaemia was induced by maximal exercise, in group B (n=15) by intravenous infusion of dipyridamole. In group A, the mean washout was 52%, and in group B it was 34% (P<0.001). The delayed upta ke rate D was significantly higher after dipyridamole. 58.4 cps, than after exercise, 44.5 cps (P<0.05). There was no significant difference in I between the two groups. The findings regarding D and I explain t hat the washout is slower after dipyridamole than after exercise, as t he mean D/I ratio was 0.48 in group A and 0.66 in group B (P<0.001).