Detector Characterization of a High-Resolution Ring for PET Imaging of Mice Heads With Sub-200-ps TOF

Positron emission tomography (PET) stands out as a highly specific molecular imaging technique. However, its detection sensitivity remains a challenge. The implementation of time-of-flight (TOF) PET technology enhances sensitivity by precisely measuring the time lapse between the annihilation photons. Moreover, by characterizing scattered (Compton) events, the effective sensitivity of PET imaging might significantly be enhanced. In this work, we present the scatter subsystem of a 2 layers preclinical TOF-PET scanner for mice head imaging. The scatter subsystem is composed of eight identical modules based on analog silicon photomultipliers (SiPMs) coupled to crystal arrays of $24\times 24$ LYSO pixels with 0.95 mm $\times 0$ .95 mm $\times $ 3 mm dimensions. The system has 29-mm bore and 50.8-mm axial length. An average CTR of $192~\pm ~1$ ps was obtained for the whole subsystem at the photopeak energy range after energy and timing corrections, and CTR values as good as 155 ps were found for some individual pixels. The transit time spread at the SiPM level was also studied and corrected, achieving a mean value of 41 ps of maximum time difference at the sensor corners with respect to the center. Voronoi diagrams were implemented to correct for position decoding.