Design and development of a fNIRS system prototype based on SiPM detectors

Functional Near Infrared Spectroscopy (fNIRS) uses near infrared sources and detectors to measure changes in absorption due to neurovascular dynamics in response to brain activation. The use of Silicon Photomultipliers (SiPMs) in a fNIRS system has been estimated potentially able to increase the spatial resolution. Dedicated SiPM sensors have been designed and fabricated by using an optimized process. Electrical and optical characterizations are presented. The design and implementation of a portable fNIRS embedded system, hosting up to 64 IR-LED sources and 128 SiPM sensors, has been carried out. The system has been based on a scalable architecture whose elementary leaf is a flexible board with 16 SiPMs and 4 couples of LEDs each operating at two wavelengths. An ARM based microcontroller has been joined with a multiplexing interface, able to control power supply for the LEDs and collect data from the SiPMs in a time-sharing fashion and with configurable temporal slots. The system will be validated by using a phantom made by materials of different scattering and absorption indices layered to mimic a human head. A preliminary characterization of the optical properties of the single material composing the phantom has been performed using the SiPM in the diffuse radial reflectance measurement technique. The first obtained results confirm the high sensitivity of such kind of detector in the detection of weak light signal even at large distance between the light source and the detector.