Detailed investigation of transmission and emission data smoothing protocols and their effects on emission images

Measured attenuation correction in PET, is routinely performed using transmission scans. Acquisition time and noise considerations necessitate low pass filtering of the transmission data, before generating the attenuation correction matrix. This smoothing operation reduces noise propagation from transmission into emission data, but also introduces image artifacts which are mostly pronounced around areas of strongly varying attenuation coefficients. The source of these artifacts, which lies in the mismatch of the spatial resolutions of emission and transmission data, was investigated in this study. The effects of different transmission and emission sinogram smoothing protocols on the emission images were also investigated. A method is proposed that addresses the problem, in coordination with the filtering step during reconstruction. Instead of the standard low pass filtering of the emission data during reconstruction, emission and transmission sinograms can be filtered to the desired reconstructed image resolution prior to reconstruction. This operation reduces or eliminates resolution mismatch and consequent image artifacts, which can be significant, especially in cardiac studies. The proposed method improves the accuracy of the activity distribution in the emission images, with minimal computational and SNR cost