Timing, Energy, and Spatial Characterization of Highly Sampled Monolithic PET Detectors With Different Thicknesses

The HyPET project proposes a hybrid dedicated time of flight-positron emission tomography for prostate imaging, with pixelated detector blocks in the front layer and monolithic blocks in the back layer. In this work, four detector configurations have been experimentally evaluated for the rear detector layer. The detector configuration consists of LYSO monolithic blocks with the same size (25.4 mm $\times25.4$ mm) but different thicknesses (5, 7.5, 10, and 15 mm) coupled to the same silicon photomultiplier array. Each detector configuration has been experimentally characterized in terms of time, energy, and spatial resolution by scanning the crystal surface using a fan beam in steps of 0.25 mm. Regarding spatial resolution, the interaction position was estimated using a neural network technique. All resolutions except energy, which remains nearly constant at 17% for all cases, show better values for the 5-mm detector thickness. We have achieved spatial resolution values of full width at half of the maximum of 1.02 ± 0.10, 1.19 ± 0.13, 1.53 ± 0.17, and 2.33 ± 0.55 mm, for 5, 7.5, 10, and 15 mm blocks, respectively. The detector time resolution obtained was 275 ± 26, 291 ± 21, 344 ± 48, and 433 ± 45 ps, respectively, using the energy-weighted average method for the time stamps.