Quantitative analysis of myocardial ischaemia on end-diastolic thallium 201 perfusion images.

ECG gating of images with thallium 201 (201Tl) may improve the representation of myocardial perfusion by allowing isolation of the end-diastolic (ED) portion of the cardiac cycle. To characterize this phenomenon, circumferential distribution profiles for ED and conventional total-cycle images (TC) with 201Tl were analysed after summing ECG gated acquisitions; redistribution was defined as net washing of 201Tl for specific myocardial segments visualized on the left anterior oblique images. Scintigraphic data were compared with the presence of coronary stenoses in 150 patients. ED images had relatively less activity in the inferoseptal and inferoapical region than TC profiles. The ED mode of washout analysis provided more frequent confirmation of visually suggested redistribution than did the TC mode (84% incidence of net wash in for ED, 69% for TC). ED analysis showed a higher incidence of net 201Tl wash in in relation to critical circumflex and left anterior descending artery lesions, but yielded a similar overall performance to TC analysis in distinguishing patients with diseased coronary arteries from normal subjects. Thus, in selected cases, analysis of ED images could assist in confirming 201Tl redistribution.