A trapezoidal slat crystal (TSC) PET detector

We report on initial performance characteristics of a trapezoidal, slat crystal (TSC) PET detector module with depth of interaction (DOI) positioning capability. The trapezoidal detector geometry supports very high packing fraction for a ring-style PET detector system. The slat design allows DOI positioning using a single-ended readout approach by including a model of the depth dependent light response function along the long axis of the crystal. We envision this style detector to be ideal for multi-modality PET/MR imaging systems and also for very compact PET only designs. We report on initial performance characteristics of TSC PET detector comprised of six LYSO slat crystals. Each of the slats is 8 mm tall, 28.8 mm long, and 0.65 mm wide on the entrance surface and 0.93 mm thick on the exit surface. Mirror film of varying lengths is used to control light sharing within the crystal array. The TSC array was coupled to a two-dimensional SiPM array of 3.74 mm by 3.74 mm sensors with 4.1 mm center-to-center spacing. While the SiPM tile consists of an 8×8 array of sensors, the TSC detector was symmetrically placed over a 2×8 set of SiPMs. A three-dimensional statistics-based method was used for event positioning. Decoding which of the six slats an event was detected in was excellent. The average peak to valley ratio of the crystal map was 3. The average intrinsic spatial resolution along the long axis of the crystal was ~1.35 mm FWHM after correcting for source size. One of the factors that limited the intrinsic spatial resolution was the photon detection efficiency of the SiPM devices that we used. In future work we plan to use SiPM arrays with greater than twice the photon detection efficiency and expect to achieve an intrinsic spatial resolution along the long axis of the crystal of better than 1.0 mm FWHM.