Attenuation correction in 3D PET-comparison of the direct and the reconstruction-reprojection method

Two methods for attenuation correction in 3D positron emission tomography have been compared. The first method, which is referred to here as the direct method, estimates the attenuation correction factors from the ratio of the blank and transmission scan. The second method, referred to here as the reconstruction-reprojection method is based on the reconstruction and forward projection of a transmission image. Using computer simulation, it is shown that the reconstruction-reprojection method significantly increases the signal-to-noise ratio in the corrected 3D emission scan, but leads to only a limited improvement in the image. A similar image signal-to-noise ratio can be obtained using the direct method, if the transmission scan is first convolved with a 3-point smoothing window. The consequence of the loss of resolution caused by this smoothing is analysed using a simulated chest phantom