Left ventricular volume: physical basis for attenuation corrections in radionuclide determinations

Absolute left ventricular volume has been calculated from gated blood pool studies by estimating an attenuation correction for left ventricular counts. The physical basis of these corrections was studied by evaluating x-ray photon attenuation from CT scans of the thorax. CT numbers were converted to linear attenuation coefficients (LACs) at 140 keV, and LACs from the center of the left ventricle or esophagus to the chest wall were determined in 12 patients of various body habitus. The mean LACs were virtually identical but were less than the LAC of water. These results suggest that conventional methods overestimate attenuation and show that LAC variability between individuals can be large. Better methods of attenuation correction may improve count-based estimates of left ventricular volume