Improving Scatter Correction for Ga-68 PSMA PET Studies

Ga-68 Prostate Specific Membrane Antigen (PSMA) is currently used in prostate cancer PET imaging. The resulting images corrected for scatter using standard/distributed software show high uptakes in the kidneys and the bladder which could produce a halo-artifact which potentially masks metastasis lesions at the level of any tracer accumulating structure such as kidney or bladder. This artifact was attributed to scatter over-correction when neglecting the prompt gamma contribution. In previous work, we have shown clinically relevant improvement in selected clinical studies, when adding a prompt gamma contribution to our standard single-bed position 3D scatter correction. The latter is based on relative scatter estimation using single scatter simulation followed by axial scaling. The axial scaling uses scatter tail fitting in an attempt to compensate both the effect of ignoring multiple scatter and out-of-axial-FOV activity. This work demonstrates further reduction in residual artifacts by replacing the one-bed SSS with a whole-body (multi-bed) one. When considering a long virtual scanner, the activity and the attenuation distributions are almost inside the axial FOV and the axial scaling accounts only for neglecting multiple scatter. The timing performance of the new algorithm is presented. An advantage of the multi-bed scheme is the uniformity of the 3D plane scaling factors especially in the bed overlap region. The new method is tested on clinical data with a Siemens mCT system and acquired by Technische Universität München, Germany.