High spatial resolution time of flight PET detectors for brain imaging.

In this work we evaluate PET detector prototypes which combine and surpass the HRRT and BrainPET detector capabilities. Our goal is to assess the feasibility of constructing higher performance brain PET systems. Several different geometries of detectors were investigated. Detector modules comprising a 5 × 5 or 10 × 10 array of 3.2 × 3.2 × 20 mm 3 or 1.6 × 1.6 × 15 mm 3 LSO crystals, respectively, were read out by a 4 × 4 element array of silicon photomultipliers. Such detector configurations do not allow depth-of-interaction determination, but provide excellent spatial and coincidence timing resolution of 192 ps and 214 ps FWHM, respectively. Two other configurations with depth-of-interaction capability were constructed. The simplest realization consists of 5 × 5 air coupled LSO crystals, 3.2 × 3.2 × 10 mm 3 in size, arranged in two stacked layers. The crystals of the top and bottom layers were selected to differ by their light outputs and decay times. The second is a triple layer detector built with a bottom layer of 4×4 elements, 4 × 4 × 10 mm 3 in size, a middle layer of 6 × 6 elements, 2 × 2 × 10 mm 3 in size, and a top layer of 5 × 5 elements, 2 × 2 × 10 mm 3 in size. The triple layer detector had 3M ESR foil in between the pixels to enhance pixel separation. To understand how the pixelation influenced our timing results single continuous LSO blocks 16 × 16 × 20 mm 3 and 16 × 16 × 16 mm 3 in size were also tested.