Abstract
In this work, we investigate some major issues for the use of silicon photomultiplier (SiPM) devices in continuous wave functional near-infrared spectroscopy (CW fNIRS). We analyzed the after-pulsing effect, proposing the physical mechanism causing it, and determining its relevance for CW fNIRS. We studied the SiPM transients occurring as the SiPM device goes from the dark (LED in off state) to the illumination (LED in on state) conditions, and vice-versa. Finally, we studied the SiPM SNR in standard CW fNIRS operation.
Highlights
Silicon Photomultiplier devices (SiPM) are very promising to advance Continuous Wave Functional Near Infra-Red Spectroscopy (CW functional near infrared spectroscopy (fNIRS)) technique for human brain cortex monitoring [1,2,3,4]
SiPM devices are very promising for CW fNIRS since they allow very high responsivity and signal-to-noise ratio (SNR)
A more important effect to take into account is the temperature change as the SiPM device goes from the dark condition (LED in off-state) to the illumination condition (LED in on-state), and vice-versa
Summary
Silicon Photomultiplier devices (SiPM) are very promising to advance Continuous Wave Functional Near Infra-Red Spectroscopy (CW fNIRS) technique for human brain cortex monitoring [1,2,3,4]. Each optode (detector – optical source pair) performs a measurement of the O2Hb and HHb concentrations in a specific region of the brain cortex defined by the optode position on the scalp and the relative distances between the detector and the light source, the last providing the in-depth To this purpose a number of light sources (generally LEDs or laser diodes) positioned on the patient head surface are alternately multiplexed, i.e. switched on and off, while the detectors collect the photocurrent due to the light back-diffused at the head surface. Some artifacts were observed and, to implement a real-time SiPM based fNIRS system, these need to be carefully analyzed and understood For this purpose, in this paper we describe which artifacts are present in the transient due to the SiPM devices when the LED sources are switched on or off. In reverse bias in Geiger mode, the SiPM temperature was estimated by the temperature dependence of the dark current, as described
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