Diffuse optical imaging of biological tissue is a well-established methodology used to measure functional information from intrinsic contrast due to hemoglobin, water, and lipid. This information is exploited in frequency domain diffuse optical spectroscopy (FD-DOS) systems, which have been used to investigate chemotherapy response, optical mammography, and brain imaging. FD-DOS depth sensitivity and dynamic range are typically constrained by photodetector sensitivity. Here we present FD-DOS utilizing a silicon photomuhiplier (SiPM) detector that has a higher signal-to-noise ratio (SNR) compared to an avalanche photodiode (APD), and thus enables extended source-detector (S/D) separations and increased depth penetration. We find the SiPM to have 10-30 dB greater SNR than a comparably sized APD while detecting 1.5-2 orders of magnitude lower light levels, down to similar to 4 pW at 50 MHz modulation. The SiPM and APD recover optical property values of tissue-simulating phantoms within 13% agreement and are stable with 1% coefficient of variation over one hour. Finally, the SiPM is used to accurately recover optical properties in a reflectance geometry at S/D separations up to 48 mm in phantoms mimicking human breast tissue. (C) 2019 Optical Society of America
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