Advantage of the four-layer DOI information in the time resolution for a TOF-PET detector

Time-of-flight position emission tomography (TOF-PET) is a promising technique for greatly improving image quality. It is well known that depth of interaction (DOI) information can reduce parallax error and uniform the spatial resolution in whole FOV. In this work, we developed three types of DOI detector (non-DOI, 2-layer and 4-layer) for TOF-PET and confirmed whether DOI information can also improve time resolution. The crystal blocks consist of a 16 × 16 Lu1.8Gd0.2SiO5 (LGSO) array. To become the same sensitivity for all crystal blocks, they had the total length in depth direction of the crystal blocks are the same. The size of each crystal element was 3 mm square. The crystal blocks were optically coupled to a 64-channel position sensitive photomultiplier tube, which has 8 × 8 multi anodes at intervals of 6.08 mm. Irradiating 511 keV gamma rays uniformly, All crystal elements of each block are clearly separated on a two-dimensional position histogram. Energy resolutions of non-DOI, 2-layer and 4-layer DOI detectors are 11.1%, 12.0% and 13.0% and time resolutions are 450 ps, 455 ps and 476 ps, respectively.