FREQUENCY OF EXTRA-CARDIAC ACTIVITY AND ITS EFFECT ON TC-99(M)-MIBI CARDIAC SPET INTERPRETATION

There are limited published data concerning the frequency and relative intensity of abdominal activity on Tc-99(m)-methoxyisobutyl isonitril e (Tc-99(m)-MIBI) myocardial perfusion scans and its effect on interpr etation. We undertook a blinded prospective study to evaluate (1) the frequency and intensity of abdominal activity on single photon emissio n tomography (SPET) scans, (2) its effect on separate evaluation of re st and stress SPET images, and (3) its effect on clinical interpretati on. Patients undergoing one-day rest-stress Tc-99(m)-MIBI scans were r andomized to receive Tc-99(m)-MIBI obtained from one of two radiopharm acies. The rest plus exercise or rest plus intravenous dipyridamole sc ans of 303 patients were scored separately by three physicians for (1) intensity of abdominal activity and (2) its effect on scan evaluation . Nuclear reports generated independently of the blinded evaluation we re reviewed to assess the effect of abdominal activity on clinical int erpretation. There were no statistical differences between pharmacies. Abdominal activity was uncommon on the exercise but common on the res t and dipyridamole scans. The exercise scans differed from the rest an d dipyridamole scans in the subgroups: intensity of abdominal activity equal to myocardium, and greater than myocardium (P < 0.001). There w as no difference between the rest and dipyridamole scans. The effect o n evaluation was moderate in 5% of the exercise, 46% of the dipyridamo le and 37% of the rest scans, and severe in 1% of the exercise, 3% of the dipyridamole and 12% of the rest scans. Rest differed from exercis e (P < 0.001) and from dipyridamole (P < 0.05). There was no differenc e between the dipyridamole and exercise scans. Based on the clinical r eports, abdominal activity was a limitation to scan interpretation for 20 patients; in 5, the inferior wall could not be evaluated. Although abdominal activity was frequently observed on both the dipyridamole a nd rest scans, it was a limitation to clinical interpretation in a sma ll fraction of the patients.