Time-gated photon counting in both confocal and offset configurations for cost-effective enhancement of functional near-infrared spectroscopy

Time-of-flight functional near-infrared spectroscopy (fNIRS) is a promising technology for non-invasive functional neuroimaging due to the capability to monitor absolute blood oxygen information. Moreover, it holds promise in addressing the spatial resolution limitations of continuous-wave fNIRS through the confocal array. However, ToF-fNIRS requires extensive data measurement and transmission, complex channel calibration, as well as high costs. Perhaps more importantly, absolute value is unnecessary in fNIRS. In light of this, a time-gated photon counting is designed to facilitate the acquisition of depth-resolved data in both confocal and offset optode configurations for cost-effective enhancement of functional near-infrared spectroscopy. To demonstrate the capabilities of the developed system, measurement performance analysis and image performance evaluation are conducted on the experimental data. The findings have demonstrated the efficacy and viability of the developed system: achieving a fluctuation level below 0.5%, relative quantitative enhancement of 32.9%, alongside improvements of 31.6% in signal-to-noise ratio, and 29.5% in spatial resolution during reconstruction. In summary, this time-gated photon counting fNIRS imaging system has the imaging quality equivalent to traditional time-correlated single-photon counter measurement in a cost-effective manner, thereby significantly augmenting the expansiveness of fNIRS-linked studies in the daily life.