SIGNAL-TO-NOISE RATIOS FOR ATTENUATION CORRECTION IN PET IMAGING

Attenuation correction is an important part of accurate image reconstr uction in positron tomography. The usual correction method involves di rect measurement of attenuation correction factors (ACF's). A reconstr uct-reproject method, which has been suggested as providing superior n oise properties, is sometimes employed; an attenuation image is first reconstructed from the measurement and then ACF's are obtained by repr ojection through this image. In this paper, we present a model which f ollows the signal-to-noise ratio (SNR) through the attenuation correct ion by both the direct and reconstruct-reproject methods. This model i s applicable to both 2-D and 3-D imaging geometry, but applies to the central elements of emission and transmission objects with circular sy mmetry and constant amplitude. For this simplified geometry, the model predicts that the SNR of the emission image following attenuation cor rection is the same for both direct and reconstruct-reproject methods, although the SNR's of the ACF's are themselves substantially differen t. This paper also presents the measured SNR at the various steps of a ttenuation correction for both the direct and reconstruct-reproject me thods using simulated transmission and emission data. The measured SNR 's agree with the model; no significant difference between the direct and reconstruct-reproject SNR's was observed.