Design of a high resolution and high sensitivity scintillation crystal array with nearly perfect light collection

Spatial resolution improvements in Positron Emission Tomography can be achieved by developing detector arrays with finer resolution elements. To maintain high sensitivity and image quality, the challenge is to develop a finely pixellated scintillation crystal array with both high detection efficiency and high light collection. High detection efficiency means the crystals must be relatively long and tightly packed. Extracting a high fraction of the available scintillation light from the ends of long and skinny crystals proves to be very difficult and there is a strong variation with light source depth. The result is inadequate energy resolution. To facilitate light collection, the crystals must be highly polished, which significantly increases costs and complexity. In this paper we examine this poor light collection phenomenon in more detail. We also describe a novel solution we are developing for readout of an array of 1×1×10 mm³ crystals using avalanche photodiodes (APD). We demonstrate through optical photon tracking simulations that the crystal light collection for this new design is nearly perfect (≥95%) and is independent of the crystal length, width, and surface treatment and origin of the light created.