Optimizing the performance of a PET detector using discrete GSO crystals on a continuous lightguide

We are designing a new detector for PET scanners using discrete 4 x 4 x 10mm(3) GSO(Ce)crystals on a continuous lightguide with 39mm photomultiplier tubes. The lightguide is designed to optimize identification of the 4 mm crystals while also minimizing the detector dead area for a given event, thereby reducing pulse pileup at high count rates. Our simulations show that a 1.8cm thick lightguide produces a narrow Light Response Function (LRF) with good crystal discrimination. The LRF describes the spread of light from the crystal to the PMT array. Further improvement is achieved by extending the lightguide to 2.3 cm in thickness, but with 0.5 cm slots cut in its front surface, which results in reduced tails of the LRF. The slotted lightguide also minimizes the spatial dependence of event positioning on different depths of interaction of the gamma ray. Experiments are in general agreement with the simulations. The good spatial resolution and narrow LRF of such a detector will result in high performance for a PET scanner which is based on the GSO detector.