Nmis - 07 Submitted to Ieee Transactions on Nuclear Science , March 2002 Second

We consider detection of high-energy photons in PET using thick scintillation crystals. Parallax effect and multiple Compton interactions such crystals significantly reduce the accuracy of conventional detection methods. In order to estimate the photon line of flight based on photomultiplier responses, we use asymptotically optimal nonlinear techniques, implemented by feed-forward and radial basis function (RBF) neural networks. Incorporation of information about angles of incidence of photons, significantly improves accuracy of estimation. The proposed estimators are fast enough to perform detection, using conventional computers. Monte-Carlo simulation results show that our approach significantly outperforms the conventional Anger algorithm. I. INTRODUCTION ETECTION of high-energy photons emitted as the result of positron decay is one of the most important low-level stages in PET imaging. In this paper we consider a detector based on the Anger scintillation camera [1]. Incident high-energy gamma quanta, generated due to positron decay, produce scintillation effect in the crystal. As the result, a shower of low energy photons in the visible and UV spectra is emitted. These photons are collected by an array of photo-multipliers (PMTs), optically coupled to the scintillation crystal, and invoke electric impulses in them. The PMT responses are utilized in estimation of the scintillation point coordinates. A non-collimated Anger camera, based on thick crystals with high photon penetration depth such as NaI(Tl), is considered in this work. Application of such thick crystals in PET scanners is desirable, due to their low cost and very high light output; they were previously used primarily in gamma ray astronomy [2]. The majority of existing scintillation position estimation