Investigation of a continuous crystal PSAPD-based gamma camera

Position-sensitive avalanche photodiodes (PSAPDs) have recently been proposed as optical light detectors in scintillation based gamma cameras. They are compact solid-state devices that provide high quantum efficiency and gain, and they can achieve precise positioning over relatively large surfaces with few readout channels. In previous studies, PSAPDs were coupled to scintillator arrays and the imaging task consisted in identifying the crystal of interaction. In this paper, we investigate the possibility of using a PSAPD to read the light of a single continuous crystal. Such a configuration has the potential to reduce the cost and simplify the construction of a PSAPD-based gamma camera while maintaining good overall performance. The spatial resolution of a small imaging unit having a continuous scintillator coupled to an 8×8 mm² PSAPD was evaluated at different energies for CsI:Tl and LaBr₃:Ce crystals. After correcting the images for the distortion and the minification associated with this camera, spatial resolution values of 0.62, 0.72, 0.99, and 1.25 mm (FWHM) were obtained for ^99mTc (140 keV), ⁵⁷Co (122 keV), ²⁴¹Am (60 keV), and ¹²⁵I (30 keV) respectively for an 8×8×1 mm³ CsI:Tl crystal. Corresponding values of 0.55, 0.64, 0.92 and 1.10 mm (FWHM) were obtained from a 1 mm thick LaBr₃:Ce crystal. These results, reproduced by Monte Carlo simulations, suggest that the continuous crystal configuration is an attractive approach to develop a PSAPD-based high-resolution gamma camera and is especially well suited for a small-animal imaging system.