A SiPM-Readout ASIC for SPECT Applications

In this paper, we present ANGUS, an application specific integrated circuit (ASIC) for silicon photomultiplier (SiPM) readout designed for low-energy gamma imaging (140 keV), specifically targeting clinical single photon emission computed tomography (SPECT) applications based on Angertype detectors. The chip is composed of 36 channels, each featuring a current conveyor input followed by an RC filter with a time constant programmable from 200 ns up to 10 mu s, a baseline holder and a peak stretcher stage. Multichannel readout is performed with a polling strategy thanks to two analog multiplexers. The chip has been designed to cope with input capacitance values of several nanofarad, like the ones featured by the large-sized SiPM pixels (8 mm x 8 mm) of the application. Despite being conceived for operation with slow scintillator crystals like cesium-iodide (CsI), this ASIC can successfully manage the readout of faster crystals like lutetium-yttrium oxyorthosilicate. Measurements of the ASIC carried out on a fully equipped SPECT detection module have shown an energy resolution of 13.7% at the 140-keV line of 99mTc, for a 5 cm x 5 cm gamma camera consisting of a continuous CsI crystal and a SiPM detection plane cooled at 0 degrees C.