Recent studies have shown that the sensitivity of conventional thallium-201 scintigraphy can be increased by the quantitative assessment of myocardial radiotracer clearance rates in conjunction with the evaluation of radionuclide uptake. In this study, a similar analysis of tomographic scintigrams was performed to determine the feasibility and value of this approach, particularly in estimating the extent of disease and detecting three vessel coronary involvement. Seventy patients undergoing cardiac catheterization for chest pain were studied by exercise and 3 hour delayed thallium-201 scintigrams using the seven-pinhole tomographic technique. Each study was evaluated by visual inspection of the tomographic sections and quantitative analysis. The latter approach consisted of comparing circumferential profiles of the initial post-exercise radionuclide uptake and the 3 hour clearance rates generated from each of three left ventricular slices with similar profiles representing the lower 95% confidence limits derived from 15 middle-aged volunteers. An abnormality was considered present when a patient's profile fell below these limits for a 30 degrees arc, and was ascribed to disease in a particular artery when it involved that vessel's usual distribution. Among the 61 patients without apparent primary myocardial or valvular disease, the diagnostic sensitivity of thallium scintigraphy was increased from 86% (43 of 50) to 96% (48 of 50) without a change in specificity (both 9 of 11 or 82%). More importantly, the quantitative approach permitted detection of 85% (107 of 126) of significantly obstructed coronary vessels compared with 47% (59 of 126) by visual analysis (p less than 0.001), again without sacrificing specificity (85 versus 87%).(ABSTRACT TRUNCATED AT 250 WORDS)