Sub-millimeter intrinsic spatial resolution PET detector designs using Geiger-mode avalanche photodetectors

We propose two ultra-high resolution PET detector designs using metal resistive-layer semiconductor photodetectors (MRS-PDs). The goal for each design is to achieve an intrinsic spatial resolution of <0.7 mm FWHM. MRS-PDs are a new type of photodiode with Geiger mode operation that can provide a proportional signal to an input photon flux. Current devices are fabricated with 1 mm by 1 mm active areas. The main limitations of these devices for PET detectors is their limited quantum efficiency for blue wavelength light, as produced by most fast, dense scintillators such as LSO, LYSO, and LFS. The basic detector unit will consist of a very thin slab crystal coupled to an array of MRS-PDs. To achieve sufficient detection efficiency, a detector module will consist of a stack of slab detectors. The first design uses linear arrays of blue to green wavelength shifting (WLS) fibers coupled to MRS-PDs as strip sensors for position decoding. Orthogonal sets of fibers will be used on both sides of a thin crystal to provide X and Y readout. The second design uses a two-dimensional array of MRS-PDs for crystal readout. The MRS-PD array may be coupled directly to the crystal or via a thin sheet of wavelength shifting material. To reduce the number of readout channels, we propose to sum rows and columns of the devices to effectively create strip detectors. Energy spectra have been collected from MRS-PDs directly coupled to LSO and via WLS fibers with promising results