Investigation of scintillation light multiplexing for PET detectors based on position sensitive avalanche photodiodes

Dedicated high resolution compact PET systems are being developed for breast and small animal imaging that use lutetium oxyorthosilicate (LSO) crystals (1×1×3 mm³) coupled to highly compact position sensitive avalanche photodiodes (PSAPDs) with 8×8 mm active area and 200 μm thickness. The full system will consist of thousands of PSAPDs. In this paper, we investigated methods to multiplex scintillation light from the LSO crystals in order to significantly reduce the number of PSAPDs required without compromising the system performance. Initial experiments were performed using dual-layer slotted LSO crystals forming crystal pixels that are offset with respect to either layer by half crystal pixel width in either 1D or 2D configuration. For the 1D crystal configuration, the results show that all crystal pixels (1×1×3 mm³ ) except the edge crystal pixels can be resolved with an average of 3:1 peak-to-valley ratio when a specular reflector is used between the crystal slots. An average energy resolution of (∼13%) is also obtained. Compared to the 1D offset crystal configuration, the 2D offset crystal configuration showed slightly better performance with an average energy resolution of (∼12%) and peak-to-valley ratio of (∼4.5:1). This result is comparable to the previous published data using discrete single layer crystal arrays. A relatively uniform photo peak energy distribution (standard deviation σ < 0.3 volts) is also observed. The result showed that light multiplexing using dual layer LSO crystals with offset crystal slot configuration has great potential. In addition, the slot crystal offset mechanism will simplify the mechanical assembly of the crystals.