Influence of adipose tissue on muscle oxygenation measurement with an NIRS instrument

The influence of the subcutaneous adipose tissue on near infra-red light propagation in leg muscle and on the sensitivity of NIR O 2 monitor is investigated. The simulation model is half infinite medium consisting of skin, adipose and muscle layer. The optical properties of each layer are chosen from the reported data and the absorption coefficient of muscle is rectified by using experimental results. The thickness of adipose layer is varied from 0 - 15 mm and the partial optical pathlength in the muscle layer and the spatial sensitivity profile are predicted by Monte Carlo simulation. The spatial sensitivity profile tends to distribute in the adipose layer and the detected light only grazes the muscle layer. These results suggest that the sensitivity in oxygenation of muscle tissue is impaired by influence of the adipose tissue and NIR O 2 monitor mainly detects the oxygenation change in shallow region of the muscle layer.