Reconstruction-reprojection processing of transmission scans and the variance of PET images

Two methods for processing noisy transmission sinograms are compared on the basis of the sample variances of emission images reconstructed from simulated data. The first method, reconstruction-reprojection, reconstructs a transmission image, and then reprojects and exponentiates it to form a smoothed set of attenuation correction factors. The other method low-pass filters each projection in the transmission data. It showed analytically that reconstruction-reprojection significantly reduces the variance of the attenuation correction factors even when the reconstruction step uses a ramp filter. Simulations were done to determine whether this reduction emission image when compared to low-pass filtering. The results of these simulations are presented