Thallium circumferential profiles in the detection of coronary artery disease ― assessment by receiver operating characteristic curve analysis

Thallium uptake and redistribution in the myocardium was quantitated using circumferential activity profiles. The profiles were determined from images in the LAO 35, LAO 70 and anterior views, obtained after peak exercise and after 3-4 h redistribution. A retention curve was constructed from these profiles, displaying the redistribution profile as a fraction of the stress profile. Normal values were obtained from 21 normal patients and compared to the images from 68 patients suspected of having coronary artery disease (CAD). Of the latter, 20 had normal/non-significant CAD and 48 had 70% or greater stenosis of one or more vessels on coronary angiography. Several methodological variations were examined: calculation of the profiles using the peak or average counts around the ventricle, uniform or interpolative background subtraction, normalisation of the profiles to their peak or mean counts. Receiver operating characteristic (ROC) curves were generated for profiles calculated using these variations and compared with the ROC curves obtained by visual interpretation of both analogue and computer-enhanced images by two experienced observers. The uniform background subtraction method was found to be better than the interpolative method, and normalisation to the mean of each curve was preferable to normalisation to the peak. ROC curves using profiles calculated using the peak myocardial counts were identical to the ROC curves from profiles using the average counts, but the operating points on the two curves differed. Computer enhancement of the digital images resulted in increased sensitivity for CAD without loss of specificity when compared to the interpretation of the analogue images. The circumferential profiles were found to provide a further increase in sensitivity and were highly reproducible.