REDUCTION OF TRUNCATION ARTIFACTS IN FAN-BEAM TRANSMISSION BY USING PARALLEL BEAM EMISSION DATA

We describe a method which uses the measurement of both photopeak and Compton scatter energy window images from a parallel beam collimation to augment the truncated attenuation map reconstruction in a fan beam transmission system. The method first estimates the body and lung outl ines from the reconstructed emission data and truncated attenuation ma p. Based on the outline information, an assigned attenuation map is cr eated and reprojected to estimate the missed projection data, which ar e then combined with the truncated projection data for the set of comp lete data without truncation. Finally, a reconstruction using the comb ined complete data is performed to obtain the attenuation map with no truncation. We demonstrate that this method can significantly reduce t he truncation artifacts in two phantom studies and one patient study. When some portion of the heart walls stays outside the densely sampled region (defined as the region of the object that has no truncation in any projection angle), the attenuation map estimated from this method can more effectively correct for the attenuation in the emission data than the truncated attenuation map.