Simultaneous time-skew and time-walk correction for TOF-PET detector

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Time-of-flight (TOF) has become a very important technology in PET, as it reduces noise to improve the PET imaging performance significantly. To obtain a high coincidence resolving time (CRT), it is effective to eliminate inter-crystal scattering (ICS). In one-to-one readout detectors, ICS events can be easily eliminated by setting an energy window for each photo sensor. Removal of ICS events improves CRT but greatly reduces sensitivity. In this work, we developed a simultaneous time-skew and time-walk correction method that suppresses the degradation of CRT even when ICS events are used for a whole-body TOF-PET scanner. A TOF detector with one-to-one readout using fast LGSO and multi pixel photo counter (MPPC) was developed to apply the proposed correction method. To maximize the sensitivity, the crystal size was 3.1 × 3.1 × 20 mm 3 and all sides were chemically polished as the surface treatment. The fast LGSO array was optically connected to an 8 × 8 MPPC array so that the crystals and MPPCs were in one-to-one coupling. In the detector calibration, we worked to improve CRT by separating individual crystal clusters into photoelectric absorption and multiple ICSs on a 2D position histogram and performing simultaneous time-skew and time-walk correction. A pair of TOF detectors was assembled and CRT was measured. When ICS events were removed as much as possible, the CRT of 230.4 ps was obtained, but about 80% of the coincidence events were removed as ICS events. On the other hand, with all events including ICS, the CRT was 320.2 ps. Using the proposed correction method, we improved the CRT to 268.5 ps without causing sensitivity loss.