Timing estimation of the exponentiated energy-weighted average for crosshair light sharing TOF-DOI PET detector.

In TOF-PET, the method of timestamp calculation is an important factor that affects coincidence resolving time (CRT). In independent readout detectors, for one-to-one coupled detectors, the first hit (FH) timestamp is the optimal one, while in light-sharing detectors, the optimal timestamp must be calculated from multiple timestamps. The method for the latter performs energy-weighted averaging (EWA) using several photosensors with earlier timestamps, but the light distribution varies depending on the detector structure. Here, we developed an exponentiated energy-weighted averaging (EEWA) method for our previously developed light-sharing detector that limits light spreading. The crosshair light-sharing (CLS) PET detector was developed as a TOF-DOI PET detector. It uses fast LGSO crystals with dimensions of 1.45 × 1.45 × 15 mm3 arranged in a 2D crystal array with three layers of enhanced specular reflectors (ESRs) forming a loop structure within a pair of crystals. The 2D crystal array is optically connected to an 8 × 8 MPPC array. The signals of the MPPC array are individually read out and processed by using TOFPET2 ASICs. To effectively utilize multiple timestamps, the EEWA method introduces a power term to the energy, giving priority to timestamps with higher energy. Additionally, we use Lumirror to increase the light collection efficiency and we compared its performance with the ESRs. In the FH method, the CRTs of the ESR and Lumirror arrays were 250 and 232 ps, respectively. In the EWA method, the CRT deteriorated as the number of MPPCs used was increased compared to the FH method. In the EEWA method, by optimizing the number of MPPCs used and the power factor, the CRT was improved to 226 and 221 ps, respectively. In summary, we developed the EEWA method for timestamp estimation and achieved an improvement of up to 24 ps in CRT. [ABSTRACT FROM AUTHOR]