Effect of patient obesity on the accuracy of thallium-201 myocardial perfusion imaging

The effects of patient habitus (e.g., breast attenuation in women and diaph ragmatic attenuation in men) have long been recognized as factors that redu ce the accuracy of myocardial perfusion imaging. Although it has long been assumed that patient obesity effects accuracy, this has never been formally evaluated. We studied the effects of patient obesity, defined as a body ma ss index (BMI) greater than or equal to 30, on 607 patients who underwent e xercise thallium-201 single-photon emission computed tomography (SPECT), Be cause the effects of obesity are most likely mediated through increased pho ton attenuation and scatter, we also evaluated the effects of other markers of patient size: body surface area (BSA) and patient weight. Accuracy was determined by performing quantitative analysis and measuring the area under the receiver operating characteristic curve (AUC). Obesity was associated with significantly lower accuracy (AUC 0.86 +/- 0.03 vs 0.92 +/- 0.02, p <0 .05) despite similar estimates of maximal coronary blood flow las estimated by heart rate and rate-pressure product at peak exercise) and severity of coronary disease. There were no significant differences attributable to eit her patient weight or BSA. Weight and BSA correlated significantly with lef t ventricular chamber size whereas BMI did not. We conclude that the accura cy of quantitative SPECT thallium-201 is significantly reduced by patient o besity and that although BSA and weight are also associated with increased attenuation, they have no effect on accuracy, which is most likely due to t he compensating effects of increased chamber size. (C)2000 by Excerpta Medi co, Inc.