LOR-PET: a novel PET camera constructed with a monolithic scintillator ring

Conventional PET cameras are constructed with detectors which consist of arrays of discrete scintillators and photosesnsors. Arrays of very fine discrete crystals have been used in high-resolution small animal imaging. However, it is very challenging to machine and assemble discrete crystals with a size smaller than 1 mm. Thus, the arrays of fine crystals are usually very expensive. And the quality of these arrays, which is heavily depended on the vendor's skills, does not always meet the requirements. Reflectors with a thickness of 0.1 mm ~ 0.2mm are necessary to separate the individual crystals in an array. The smaller the size of the discrete crystals, the smaller the filling factor of the crystals in the array, and the smaller the sensitivity of the system. In this paper, we present a novel PET system constructed with a monolithic scintillator ring. This PET system is very different from any PET systems which have been constructed so far. It is constructed from a single piece of monolithic crystal. And the lines of response (LOR) are calculated directly from the light distribution around the crystal ring, instead of being calculated from the measurement of the positions of interaction (POI) of the two gammas. Thus, we name it LOR-PET. We have designed and constructed the first LOR-PET with a monolithic LYSO scintillator ring. The inner and outer diameters of the ring are 48.5 mm and 58.5 mm respectively. The length and thickness of the ring are 25.12mm and 5 mm respectively. Twenty-three 4x1 SiPM arrays are fabricated and mounted inside of the monolithic LYSO crystal ring. A low-cost highperformance electronics system (named Pico-PET electronics) was built to read out the 92 channels of SiPM in parallel. The results of initial tests shows that the electronics system works very well. We conclude that the LOR-PET system is a unique low-cost PET system that has the potential to achieve good sensitivity and spatial resolution in small animal or organ specific imaging. We are performing system characterization and phantom study to further assess the performance of the LORPET system.