Reduction of truncation artifacts in fan beam transmission by using parallel beam emission data

We describe a method to reduce the truncation artifacts in the fan beam transmission image reconstruction of a simultaneous transmission and emission SPECT system. Parallel hole collimation is adopted for the measurement of both emission photopeak and Compton scatter photons, which are also used to obtain the body and lung outlines. The lung outlines can be refined using attenuation coefficient (μ) estimates from within the fully sampled region (FSR) of the attenuation map computed using the truncated transmission data. The regions of the lungs and other soft tissues are assigned appropriate attenuation coefficients to create the attenuation map with no truncation, which are then reprojected to augment the transmission projection data. A match of the total attenuation between the real and reprojected data is made at each projection angle in each slice to account for the different attenuation coefficients in different slices. Finally, a reconstruction of the combined measured and augmented data is performed. We demonstrate that this method can significantly reduce the truncation artifacts using two phantom studies. When some portion of the heart falls outside the FSR, the attenuation map estimated from this method can more effectively correct for the attenuation in the emission data than the truncated map