Development of a TOF-PET detector capable of four-layer DOI encoding with a single-layer crystal array

In positron emission tomography (PET), depth of interaction (DOI) detectors are preferable for providing both high spatial resolution and high sensitivity. In previous work, we developed a four-layer DOI detector and invented and proved it works successfully for a time-of-flight (TOF) PET scanner. The detector consists of four layers of a 16 × 16 Lu_1.8Gd_0.2SiO₅ (LGSO) crystal array. Each crystal element is 3.0 mm square and 5, 6, 7, and 8 mm in depth, and the four-layer DOI encoding is allowed by changing the reflector arrangement for each layer. However, the gaps between layers degrade the performance of the detector such as the energy and time resolution. In addition, the increase in the number of crystal elements increases the assembly time of the crystal blocks. In this work, we have developed a new TOF-PET detector capable of four-layer DOI encoding with a single-layer 16 × 16 crystal array. Each crystal element of LGSO is 3.0 mm square and 26 mm in depth, but the reflector arrangement is same as in the conventional DOI-TOF detector. The crystal block is coupled to a 64-channel flat panel position sensitive photomultiplier tube which has 8 × 8 multi anodes at intervals of 6.08 mm. The proposed detector was arranged opposite a BaF₂ detector and was uniformly irradiated using 511 keV gamma rays from a ²²Na point source. All crystal elements and DOI layers were expressed on a two-dimensional position histogram without overlapping. In comparison with the conventional DOI-TOF detector, the energy resolution was improved from 13.0% to 11.2% and the time resolution was improved from 476 ps to 455 ps. These results demonstrated the proposed DOI-TOF detector is suitable for practical use by reducing cost while improving energy and time resolutions