Contrast enhancement of thallium-201 myocardial scintigrams: improved sensitivity with diminished specificity in coronary disease detection.

Thallium-201 myocardial scintigraphy (TMS) has become an increasingly popular noninvasive technique with a high diagnostic specificity, but a somewhat lower sensitivity for coronary disease (CAD) detection. Many centers now routinely employ computer techniques to contrast enhance scintigrams, but the resulting changes in sensitivity and specificity have not been carefully evaluated. In the present study, three observers with different levels of experience blindly interpreted both unprocessed and enhanced exercise TMS from 40 patients with CAD and from 15 without significant obstructions. The sensitivity for CAD achieved by each observer was higher with the enhanced scintigrams (increase from an average of 80% to 93%), but there was concomitant loss of specificity (from 93% to 73%). Similarly, significant changes were present in the sensitivity and specificity with which ischemic regions were diagnosed. In addition, contrast enhancement facilitated interpretation of TMS studies, particularly in making comparisons between exercise scintigrams and subsequent rest or redistribution images. Contrast enhancement affected the interpretations of the inexperienced observer most significantly. We conclude that contrast enhancement improves TMS sensitivity but results in some loss of specificity. The variable effect of enhancement on observers with different levels of experience suggests that laboratories should critically evaluate their own results before routinely employing computer processing.