Development of a light readout based on silicon photomultipliers for a wavelength-shifting fibre gamma camera

The concept of wavelength-shifting fibre gamma camera has been previously introduced by Soares et al. (1999), consisting of a scintillation crystal covered in both sides by two ribbons of orthogonal wavelength-shifting fibres (WSFs), which provide 2D position information when read out by photon detectors and one or several PMTs on one side of the crystal+fibres set to provide energy information. In this work, the potential of silicon photomultipliers (SiPMs) to replace PSPMTs and improve the imaging performance of the WSF gamma camera is analysed. Several aspects concerning the application of SiPMs as photon detectors for position detection in a WSF gamma camera are evaluated, such as the impact of the intrinsic noise levels of these devices and the influence of temperature and readout electronics in their output signal. l prototype of 10 SiPMs reading out 10 WSFs was assembled and used to cover a 1 cm2 imaging area with a collimated 57Co source scanned in 1 mm steps, demonstrating the feasibility of applying the SiPMs in a CsI(Na)–WSF gamma camera. Two different algorithms were used for positioning and image reconstruction, obtaining encouraging results operating at 20 °C and with a common bias voltage applied to all SiPMs. The observed dependence of the detection efficiency with temperature indicates that further cooling is necessary in order to achieve better positioning results than previous work using PSPMTs. The development of larger prototypes with detection areas up to 100 cm2 is under way, considering the use of a water cooling system for the SiPMs.