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Interobserver Variability in the Interpretation of Myocardial Images with Tc-99m-Labeled Diphosphonate and Pyrophosphate

Instituto Nacional de Cardiología Dr. Ignacio Chávez, Mexico City, Mexico

Correspondence: For reprints contact: Alfredo Cuarón, Departamento de Medicina Nuclear, Instituto Nacional de Cardiología Dr. Ignacio Chávez, Cubículo B-408, Juan Badiano I, México 22, D.F. México.

ABSTRACT

Without prior knowledge of the significant clinical data, six observers have independently evaluated a consecutive series of 250 myocardial scans made with Tc-99m-labeled phosphates: 127 with MDP and 123 with PPI. Of the 226 patients, all having acute precordial chest pain, 169 were shown to have acute myocardial infarction while 57 suffered acute distress from other causes. The six observers, varying in their experience with nuclear medicine, compared the intensity of uptake in the heart with that in bone, and rated their impression of a "positive" image by a six-category scale—that is, one with five criterion levels. Results were expressed as receiver operating characteristic (ROC) curves, from which the optimal individual criterion level for each observer was determined. We found very high interobserver variability in the perception of the shades of myocardial concentration, although they were based on strict and apparently objective criteria. This variability has a direct influence on the overall performance of each observer. In every instance, PPI was demonstrated to be a better tracer than MDP for myocardial imaging. The bias of the experience, visual perception, and psychology of the observer at the time of the reading of the images seems to be significant, as is the presence of uncorrected visual defects. These results justify the setting of special programs to evaluate periodically the performance of every physician who interprets studies, to establish his optimal individual criterion level instead of using a fixed criterion level to decide whether an image is "positive."