Gapless implementation of crosshair light-sharing PET detector

Abstract

Recently, silicon photomultipliers (SiPMs) have become established as photo-sensors for PET scanners. Commercially available SiPM arrays are typically about 3–4 cm in size. In order to develop larger detectors with an Anger calculation, multiple SiPM arrays need to be combined. This configuration requires the use of a light guide and has inactive areas between SiPM arrays. If not addressed, crystal identification degrades not only for peripheral crystals but also for crystals to bridge the gap between the SiPM arrays. On the other hand, we have developed the crosshair light-sharing (CLS) PET detector, which is based on a single-ended readout scheme with roughly quadrisected crystals comparable in size to a SiPM, with depth-of-interaction (DOI) capability. The CLS PET detector based on the local centroid calculation was expected to mitigate the edge effect similar to what the one-to-one coupling detector is able to do. In this work, we developed the axially long CLS PET detector with two multipixel photon counter (MPPC) arrays. The proposed long CLS PET detector consisted of 30 × 14 gadolinium fine aluminum garnet (GFAG) arrays coupled to two 8 × 8 MPPC arrays without the light guide. From 511-keV uniform irradiation, responses of all crystal elements could be separated clearly on a 2D position histogram after applying the Anger calculation. Pulse heights of additional crystals to bridge the gap were 18% lower than those of crystals at the center of the MPPC array, but similar to that of the peripheral crystals based on non-uniformity of the MPPC array. On the other hand, energy resolutions of additional crystals to bridge the gap were almost the same to those of other crystals. The long CLS PET detector promises improvement of the packing fraction while keeping performance.