Comparison between reference values for ²⁰¹Thallium uptake and washout from the myocardium after exercise and after dipyridamole

Summary. A slow washout of ²⁰¹Thallium has a high diagnostic and prognostic value for coronary artery disease. The aim of the present work was to contribute with reference data on ²⁰¹T1 uptake and washout from the myocardium. With a quantitative method using circumferential profiles and interpolative background subtraction we performed ²⁰¹T1 myocardial imaging in two groups of subjects with a low probability of coronary artery disease. Washout in per cent is defined as (1‐D/I) 100, where D is 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 uptake 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 that the washout is slower after dipyridamole than after exercise, as the mean D/I ratio was 0.48 in group A and 0.66 in group B (P < 00.1).