Prone versus supine thallium myocardial SPECT: a method to decrease artifactual inferior wall defects.

Artifactual inferior wall defects as a result of diaphragmatic attenuation of activity are a frequent source of error in thallium myocardial single photon emission computed tomography (SPECT) studies. Thirty-four patients and 11 clinically normal volunteers were studied prospectively to see if specificity of inferior wall defects for right coronary artery disease could be improved by scanning patients prone versus supine. All individuals were scanned both prone and supine, in random order, following symptom limited treadmill exercise. Images were acquired at 3 degrees steps, 25 sec per frame, in a 180 degrees elliptical orbit always beginning in the 45 degrees right anterior oblique position relative to the patient. Polar maps generated from the short axis slices were used to calculate the average regional activity. The prone studies showed consistently higher inferior wall activity compared to the supine studies on both the exercise (182 +/- 22 vs. 160 +/- 23, p less than or equal to 0.001) and 4-hr delay studies (183 +/- 20 vs. 175 +/- 21, p less than or equal to 0.001). Prone imaging resulted in a significantly higher specificity for RCA disease compared to supine imaging (90% vs. 66%, p less than 0.05) with an improvement in accuracy from 71% to 82%. Sensitivity, specificity, and accuracy for left anterior descending and left circumflex artery disease were not significantly affected by patient position during imaging. All patients having SPECT thallium myocardial perfusion studies should be imaged prone to minimize artifactual inferior wall defects and improve accuracy.