WSF gamma camera with SiPMs: First small animal tests

Following the introduction of the wavelength-shifting fiber (WSF) gamma camera by Soares et al. and evolution of photodiodes into highly sensitive silicon photomultipliers (SiPMs), we have assembled a WSF gamma camera applying SiPMs to individually read out 1 mm diameter WSFs carrying the position information of scintillation events in a continuous CsI(Na) crystal. Despite the challenge of using many SiPMs to read out light pulses of very low amplitude and slow decay time, at room-temperature, SiPMs show great potential to improve the spatial resolution and overall performance of the WSF gamma camera, due to their high photodetection efficiency. Moreover, they allow building a compact and low power consuming camera, aimed for breast-specific gamma imaging. Tests carried out with ⁵⁷Co and ⁹⁹mTc on a small prototype with 10×10 mm² field-of-view demonstrated the concept´s feasibility and characterized its imaging performance. A larger camera with 10×10 cm² is being developed for clinical application, but isn´t yet fully operational. Imaging of a small mouse injected with ^99mTc-HMDP was therefore carried out by performing several scans with the small prototype. Despite experimental limitations, the resulting images compared favorably to those obtained by a traditional Anger camera. Furthermore, performance can be improved by several optimizations, in order to minimize and control effects of thermal noise and non-uniformity of response of multiple SiPMs.