Near-infrared spectroscopy system with non-contact source and detector for in vivo multi-distance measurement of deep biological tissue

A non-contact near-infrared spectroscopy (NIRS) scanning system with a phosphor cell placed on the skin for in vivo measurement of biological tissue was developed and evaluated. Because the phosphor is excited by the light that propagates in the tissue, and the excitation light is cut by optical filters, the light that propagates in the tissue is selectively detected. The non-contact system was extended to create a scanning system that can flexibly change source positions with a galvano scanner. The optical scanning system was used for non-contact measurement of the human forearm muscle, and the dependence of optical-density change (ΔOD) caused by the upper-arm occlusion and release on source-detector distance was observed. The obtained ΔOD demonstrates the effectiveness of using this system for multi-distance human-forearm measurement. Furthermore, a human forehead was measured with the system. To extract a deep-layer signal, a surface-layer subtraction method with short-distance regression was applied to measured data. On the basis of the correlation with a simultaneously measured laser-Doppler flowmetry signal, it was confirmed that the deep-layer signal was successfully extracted. The extraction result demonstrates that the optical scanning system can be used as a multi-distance NIRS system for measuring the human brain activity at the forehead.