Problem of diffuse cardiac uptake of technetium-99m pyrophosphate in the diagnosis of acute myocardial infarction: Enhanced scintigraphic accuracy by computerized selective blood pool subtraction

Abstract

Because considerable controversy attends the interpretation of the diffuse uptake pattern of technetium-99m pyrophosphate scintigraphy, a practical computerized method for selective subtraction of the cardiac blood pool from these equivocal technetium-99m pyrophosphate scintigrams is described. The technique employs injection of a readily available radiopharmaceutical (technetium-99m pertechnetate) and standard computer software. The subtraction process allows subclassification of the equivocal scintigrams into two groups: one with definite myocardial localization of radioactivity, and the other without evidence of myocardial labeling. The clinical utility of this selective subtraction technique was assessed in 35 patients with equivocal pyrophosphate scintigrams and in an additional 13 patients with probably abnormal scintigrams by comparing the results of the subtraction scintigraphy with the final clinical diagnosis based on history, serial electrocardiograms and serial cardiospecific serum enzyme determinations. The results demonstrated that the subclassification based on computerized selective blood pool subtraction is clinically useful: If definite myocardial localization is demonstrated after subtraction, acute infarction is likely, whereas, if no myocardial localization is evident after subtraction, acute infarction is highly unlikely. Therefore, the addition of this simple selective blood pool subtraction technique to standard pyrophosphate imaging has been found to improve the overall effectiveness of pyrophosphate scintigraphy in the detection of acute myocardial infarction.