Correction of the influences of a subcutaneous fat layer and skin in a near-infrared muscle oximeter

The inhomogeneity of tissue structure greatly affects the sensitivity of tissue oxygenation measurement by reflectance NIRS. We have proposed a method for correcting the influence of a subcutaneous fat layer on muscle oxygenation measurement. The correction is based on an inverse relationship between the measurement sensitivity and detected light intensity. In this study, this method was validated by measuring the peak-to-peak variation of muscle oxygenation in periodic exercise tests on the vastus lateralis. A multisensor probe consisting of a light source and four photodiodes with source-detector distances of 7-40 mm was newly developed. A proximal detector with a 7-mm separation was used to eliminate the effect of skin. The fat layer thickness was also measured by ultrasonography. Results of the tests clearly showed that the presence of a fat layer greatly decreases the sensitivity of measurement and increases the light intensity at the detectors. Sensitivity correction by detected light intensity resulted in almost the same changes in muscle oxygenation due to periodic exercise among subjects regardless of different fat layer thicknesses. The proximal detector was also effective for reducing the effect of skin