Design and feasibility study of an ultra-fast high resolution PET detector

In this paper, we present the design and the results of a feasibility study of a novel, ultra-fast and high-resolution PET detector. It is based on the use of an LSO crystal array read-out by a Multi pixel Hybrid PhotoDiode (M-HPD) using an encoded fiber light-guide. The fiber encoding method enables one to readout more than 400 discrete crystal elements using a single M-HPD tube having 61 pixels. One of the key features of the detector is that the encoded fiber light-guide, used in conjunction with a digital readout system, eliminates the need for the use of ADCs in finding the address of the crystal in which interaction occurred. The readout time of a detector comprising around four hundred 2×2×10 mm discrete crystals, defined as the time between identifying a coincidence and providing the address of the crystal hit, can be reduced to less than 0.1 μs. As a consequence, one could significantly improve the noise-effective-count-rate (NECR) performance of a PET system based on this detector design. Another advantage of this detector design is that the parallel readout scheme used, greatly simplifies the readout electronics by eliminating the use of ADC in the readout system. The feasibility of this detector design has been confirmed by measurements using a prototype detector module based on a 5×5 array of 2×2×10 mm LSO crystals. A signal level of around 200 photoelectrons has been measured for 511 keV energy deposited in the detector. An energy-resolution of ∼30% and a timing resolution of less than 4 ns were achieved in this study.