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A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa and INFN Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst (Trento, Italy), are being evaluated for this purpose. The devices are composed of 16 (4 times4) pixel elements of 1 mmtimes1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been performed coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs. The first tests on position determination with continuous crystals and SiPM matrices have been performed. An intrinsic spatial resolution of 0.61 mm FWHM has been obtained.

We have studied the performance of two multi-pixel Geiger-mode APDs (recently developed by the Centre of Perspective Technologies and Apparatus (CPTA) in Moscow) with 1×1 mm 2 and 3×3 mm 2 sensitive area as a readout for LSO and LYSO scintillator crystals. Energy and timing spectra were measured using a 22 Na γ-source. The results of this study allow us to conclude that this photodetector is a very promising candidate for PET applications.

The AX-PET is a new geometrical concept for a high resolution 3D PET scanner, based on matrices of axially oriented LYSO crystals interleaved by stacks of WLS, both individually read out by G-APDs. A PET demonstrator, based on two detector modules used in coincidence, is currently under construction.

The effective light attenuation length in thin bars of YAP:Ce and LYSO:Ce crystals has been studied for different coatings of the lateral surfaces of the scintillators. This physical parameter plays a key role in a novel 3D PET concept based on axial arrays of long scintillator bars read out at both ends by Hybrid Photodetectors (HPD). The parameter influences the spatial, energy, and time resolutions of such a device. The expected resolutions let the novel concept appear competitive compared to existing traditional PET devices. In this paper we show that the effective light attenuation length can be tuned to the desired value by wrapping the lateral surfaces of the crystals or by coating them with layers of Cr or Au of different thickness. The studies have been carried out with long YAP and LYSO scintillator bars, read out by standard photomultiplier tubes. Even though the novel PET device is planned to use different scintillators and HPD readout, the results described here prove the feasibility of an important aspect of the concept and explore the potential resolution of the device.