Measurements for the SiliPET project: A small animal PET scanner based on stacks of silicon detectors

In this paper we propose a new scanner for small-animal positron emission tomography (PET) based on stacks of double sided silicon detectors. Each stack is composed of 40 planar detectors with dimension 60 × 60 × 1 mm³ and 128 orthogonal strips on both sides to read the two coordinates of interaction, the third being the detector number in the stack. Multiple interactions in a stack are discarded by an exclusive OR applied between each plane detector of a stack. In this way we achieve a precise determination of the interaction point of the two 511 keV photons. The reduced dimensions of the scanner also improve the solid angle coverage resulting in a high sensitivity. Preliminary results were obtained with MEGA prototype tracker (11 double sided Si detector layers, each with a thickness of 0.5 mm and a strip pitch of 470 ¿m), divided into two stacks 2 cm apart made of respectively 5 and 6 prototype layers, placing a small spherical ²²Na source in different positions. We report on the results, spatial resolution, imaging, spectral and timing performances obtained with double sided silicon detectors, manufactured by ITC-FBK, having an active area of 3 × 3 cm² and a strip pitch of 500 ¿m. Two different strip widths of 300 ¿m and 200 ¿m, and two thicknesses of 1 mm and 1.5 mm, equipped with 64 orthogonal p and n strips on opposite sides were read out with the VATAGP2.5 ASIC, a 128-channel ¿general purpose¿ charge sensitive amplifier.