A comparison of myocardial thallium-201 image quality after either dipyridamole or exercise stress.

Exercise and dipyridamole provide two mechanistically different stress techniques for thallium-201 imaging. To date, comparisons of the two have relied solely on assessments of clinical results. However, because diagnostic accuracy ultimately depends on image quality, this study was undertaken to compare the image quality obtained by both techniques. The left anterior oblique images of 30 patients, who had thallium imaging after intravenous dipyridamole (0.56 mg kg-1 over 4 min) were compared with those of 30 patients who were imaged after symptom limited, Bruce protocol, treadmill exercise in the same time period. Myocardial and lung-background thallium uptake were compared after stress and on redistribution. The ratio of the best segmental myocardial thallium uptake (M) to that in a fixed lung-background region (B) was taken as an index (M/B) of image quality. Myocardial thallium uptake was significantly higher after dipyridamole than after exercise (P less than 0.001). Lung-background thallium uptake, however, was also higher (P less than 0.001) so that the resulting image quality indices (M/B) were similar (P = NS). The redistribution images gave the same results. In both techniques myocardial and lung-background thallium uptake counts dropped significantly from stress to redistribution images, but because they declined at similar rates, the resulting image quality index (M/B) remained unchanged. Adverse effects occurred less frequently in the dipyridamole stressed group. Thallium images performed after dipyridamole stress are at least equivalent in image quality to those after exercise stress. This technical study further strengthens the clinical case for the use of the dipyridamole stress technique in routine diagnostic imaging.