Quantitative measurement of muscle hemoglobin oxygenation using near-infrared spectroscopy with correction for the influence of a subcutaneous fat layer

The inhomogeneity of tissue structure greatly affects the sensitivity of tissue oxygenation measurement by reflectance near-infrared spectroscopy. In this study, we investigated the influence of a fat layer on muscle oxygenation measurement by in vivo tests and Monte Carlo simulation, and we propose a method for correcting the influence. In the simulation, a three-dimensional model consisting of the epidermis, dermis, fat, and muscle layers was used. In in vivo tests, measurement sensitivity was examined by measuring oxygen consumption of the forearm muscle and the peak-to-peak variation of oxygenation in periodic exercise tests on the vastus lateralis using a newly developed multisensor type of tissue oximeter. Fat layer thickness was also measured by ultrasonography. The correction curve of measurement sensitivity against fat layer thickness was obtained from the results of simulation and in vivo tests. The values of corrected oxygen consumption were almost the same and had less variation between individuals $\text{(0.13±0.02\hspace{0.05em}}{\mathrm{ml 100 g}}^{\mathrm{-1}}{\mathrm{ min}}^{\mathrm{-1}})$ than did the uncorrected values $\text{(0.08±0.04\hspace{0.05em}}{\mathrm{ml 100 g}}^{\mathrm{-1}}{\mathrm{ min}}^{\mathrm{-1}}\mathrm{).}$