Abstract
We built a fiber-less prototype of an optical system with 156 channels each one consisting of an optode made of a silicon photomultiplier (SiPM) and a pair of light emitting diodes (LEDs) operating at 700 nm and 830 nm. The system uses functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) imaging of the cortical activity of the human brain at frequencies above 1 Hz. In this paper, we discuss testing and system optimization performed through measurements on a multi-layered optical phantom with mechanically movable parts that simulate near-infrared light scattering inhomogeneities. The baseline optical characteristics of the phantom are carefully characterized and compared to those of human tissues. Here we discuss several technical aspects of the system development, such as LED light output drift and its possible compensation, SiPM linearity, corrections of channel signal differences, and signal-to-noise ratio (SNR). We implement an imaging algorithm that investigates large phantom regions. Thanks to the use of SiPMs, very large source-to-detector distances are acquired with a high SNR and 2 Hz time resolution. The overall results demonstrate the high potentialities of a system based on SiPMs for fNIRS/DOT human brain imaging applications.
Highlights
Functional near-infrared spectroscopy is a non-invasive technique that uses light in the near-infrared spectral range to measure the optical properties of biological tissues
By using silicon photomultiplier (SiPM) in their linear regime, we demonstrate the feasibility of a SiPMs and light emitting diodes (LEDs) based optical imaging system able to perform a large number of overlapping measurements by exploiting SDSs from 2 to 10 cm, in a phantom with near-infrared light scattering and absorption characteristics close to human head tissues
The results clearly demonstrate the high capabilities of SiPMs for the development of human brain cortex functional imaging systems
Summary
Functional near-infrared spectroscopy (fNIRS) is a non-invasive technique that uses light in the near-infrared spectral range to measure the optical properties of biological tissues. The technique relies on the diffusive properties of the tissue under study; it works at its best on soft tissues such as the human breast and brain. In medicine, this technique is used to report blood-oxygen-level-dependent (BOLD) signals [1] via measurements of scattered light attenuation induced by hemoglobin oscillations within the cortical layers, performed non-invasively from the scalp [2]. Sci. 2020, 10, 1068 such as total hemoglobin concentration and blood oxygen saturation can be obtained. With particular focus on the human brain, optical methods can be used to assess or monitor several neurological diseases manifesting as blood oxygenation related functional or metabolic alterations in the brain, including Alzheimer’s disease [3], autism spectrum disorder [4], stroke [5], and multiple sclerosis [6]
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