Timing resolution of a TOF-DOI detector module prototype for positron emission tomography

To increase the image quality and spatial resolution in positron emission tomography (PET), organ-dedicated and large axial field of view scanners require precise correction of the parallax errors at oblique angles via depth-of-interaction methods. In addition to their large solid angle coverage, time-of-flight (TOF) information, i.e., a high coincidence time resolution (CTR), can be exploited to increase the image signal-to-noise ratio and effectively boost system sensitivity. Due to the impact of the photon travel time spread (PTS) on the TOF resolution, a high DOI resolution is essential to correct the impact of the PTS on the CTR and achieve even higher timing resolution. In this work, we present a TOF- and DOI-capable detector block with a CTR of 187 ps (FWHM) to 213 ps (FWHM), read out with the NINO and TOFPET2 ASIC, and a DOI resolution of 3.4 mm to 4.7 mm (RMSE), which distinguishes at least two DOI layers in the detector. Additionally, we established benchmarks for the CTR with custom high-frequency readout electronics. With these, a CTR of 136 ps (FWHM) can be maintained for a single TOF-DOI unit channel in the detector block.