Comparison of three approaches for timing optimization of a dual layer LSO-APD small animal PET scanner

Abstract

The application of avalanche photodiodes (APDs) for the readout of scintillation crystals offers the possibility of using compact detector modules in positron emission tomography. Good timing resolution is more challenging with APDs due to their lower gain and larger rise time in comparison to photomultiplier tubes. This study examined the different factors influencing time resolution and investigated three approaches for optimizing the time resolution of a dual layer LSO-APD small animal PET scanner. The used PET scanner (MADPET-II) features individual readout of LSO scintillation crystals (2×2 ×6mm3 front layer and 2×2×8 mm 3 back layer) by APD arrays. The system consists of 1152 LSO-APD channels arranged in a dual layer detector ring. For the purpose of this study different approaches for optimizing the time resolution were compared: A) Measurement and correction for amplitude walk in the analog part of the acquisition electronics. B) Determination of interchannel delays by two methods: B1) Measurement using a timing alignment probe. B2) Software approach based on an iterative algorithm. Method A: Distinct amplitude walk effects in the analog electronics were observed. When correcting for these, the time resolution can be reduced by 16%. Method B1: Interchannel delays, originating from amplitude- and rise time walk, of up to 40 ns were measured. The time resolution can be optimized by 40% when these delays are taken into account. Method B2: The algorithm does not determine the same interchannel delays as measured with B1 and the time resolution can be reduced by 9% when the algorithm is applied. Interchannel delays play the predominant role for the time resolution of the MADPET-II scanner. The measurement and correction of these interchannel delays improves the time resolution significantly. Further work is done to reduce the time resolution by minimizing jitter. © 2009 Springer-Verlag.