Experimental 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. 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 microns), 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, spectral and timing performances obtained with double sided silicon detectors, manufactured by ITC-FBK, having an active area of 3 x 3 cm² and a strip pitch of 500 mm. Two different strip widths of 300 μm and 200 μm, 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. Each channel is composed of a low-noise/ low-power preamplifier, a shaper (peaking time of 3.1 μs) with sample/hold, multiplexed analogue readout and a fast shaper (peaking time of 1.1 μs) that gives a trigger signal.