Epicardial fat : An unrecognized cause of artifact on myocardial perfusion imaging

Myocardial count defects are noted in regions without perfusion abnormalities, usually because of soft tissue attenuation. We present 3 examples in this report in which we found that, despite attenuation correction using standard commercially available hardware and software, focal perfusion abnormalities were seen that were anomalous, because both wall motion and wall thickening were normal as seen on both nuclear and cardiac MR imaging. These defects appear to be caused by unusually prominent focal epicardial fat as demonstrated in the accompanying examples showing epicardial fat revealed by MRI at sites coincident with count defects of the fused nuclear tomograms. In a prospective study of 21 patients with diabetes who underwent same-day cardiac magnetic resonance and Tc-99m sestamibi-gated SPECT imaging, we found that anomalous decreased counts resulting from the presence of epicardial fat was seen in 48% of patients. These apparent perfusion defects were considered to be of potential clinical significance in 10% of cases. In all cases, both visual and quantitative wall motion and wall thickness were normal. The only clinical correlates for the presence of an epicardial fat pad were body surface area and waist circumference.