_Applied_  
_sciences_  
_Article_  
**Imaging System Based on Silicon Photomultipliers**  
**and Light Emitting Diodes for Functional**  
**Near-Infrared Spectroscopy**  
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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]. Traditionally, brain function is imaged with positron emission tomography (PET) or with functional magnetic resonance imaging (fMRI). However, PET uses ionizing radiation, which is risky for health, while fMRI involves exposure to strong magnetic fields and induced electric fields, making it a contraindication in patients with implanted electronic devices (e.g., deep brain stimulators, pacemakers, and cochlear implants). Moreover, both the techniques are quite uncomfortable for the patient who is forced to lay within a small space. Optical imaging is an alternative human brain mapping technique when both fMRI and PET are not indicated. Optical systems have, in principle, a much simpler hardware, therefore, they may be suitable for a more widespread use in medical care. One of the most popular optical techniques for brain imaging is continuous wave (CW) fNIRS. CW-fNIRS evaluates light attenuation by executing cyclic measurements of diffused light from the brain cortex at multiple source-detector couples, using at least two wavelengths in the 700-950 nm range, generally at an overall measurement rate ranging from 1 to 100 Hz [7]. In each cycle, each optode (detector, dual optical source pair) performs a measurement of the oxy- and deoxy-hemoglobin concentrations in a specific region of the brain cortex defined by the optode position on the scalp and the relative distance between the detector and the light source (source detector separation or SDS), the last providing an estimation of the investigation depth. As SDS increases, the banana-shaped probabilistic path of the detected light grows and extends deeper into the brain [8]. Traditional CW-fNIRS imaging instruments provide sparse arrangements of optodes with significantly lower spatial resolution than fMRI [2]. Sparse layouts of source-detectors are suitable to obtain functional traces rather than maps or images. However, recent developments in high-density diffuse optical tomography (HD-DOT) have broadened this perspective by providing a dramatically upgraded spatial resolution [9; 10; 11; 12]. However, high-density arrays, particularly when covering a large portion of the head, present significant challenges in high-channel-count instrumentation, illumination interferences (separating signals detected from multiple sources), fiber-optic-scalp coupling, and lateral torqueing of the fibers.