PET random reduction with a FOV-dependent coincidence window and tangential TOF-mask

Time-of-flight (TOF) positron emission tomography (PET) has achieved a 500-600 ps coincidence timing resolution for clinical whole-body scanners. TOF PET has been used to narrow the coincidence window to 4-6 ns for whole-body imaging and thus reduced random coincidence rate and improved the noise-equivalent-count (NEC) rate. In this paper, we revisit the random reduction by deriving an explicit coincidence window equation, and propose a tangential TOF-mask to tailor the coincidence window to conform to the FOV without any patient morphological information. Experimental line source data at the edge of various FOVs are used to validate the coincidence window equation and TOF-mask. A new signal-to-noise ratio (SNR) formula via NEC is given with this TOF mask. Multiple FOVs of NEMA NU-2 experimental count-rate data are used to demonstrate the relative gain in NEC with this TOF mask.