Characterization of the reinjection thallium image.

Abstract

The 201TI image after reinjection was characterized by analysis of stress and reinjection data acquired in 204 consecutive patients undergoing planar 201TI cardiac stress tests. In an additional 63 patients, redistribution data were also acquired to determine the effect of washout on the final reinjection image. Maximum count densities for the myocardium, lung and liver were measured, and the ratios between the stress and redistribution and the stress and reinjection sets of data were calculated. In patients with < 5% probability of coronary artery disease (CAD) ("normal" group), the reinjection image was typified by less myocardial activity (initial/reinjection = 1.22), slightly less lung activity (initial/reinjection = 1.05) and greater hepatic activity compared to the initial postexercise image. In male patients with > 5% probability of CAD, peak myocardial activity after reinjection was affected by the following variables: the interval between stress and reinjection, the amount of the initial dose and the 201TI scan results (normal 201TI study: initial/reinjection = 1.16; abnormal = 1.06; p < 0.009). Myocardial activity after reinjection was linearly related to myocardial activity after redistribution (r = 0.82). There was no significant influence by those variables in the 76 women who were studied. In conclusion, myocardial 201TI was decreased after reinjection in normal patients. The results indicate that there is an increased likelihood of underlying CAD in male patients undergoing exercise stress tests when 201TI myocardial activity on reinjection is greater than on the initial image.