 The near-infrared diffuse optical spectroscopy can measure tissue regions deeper below the skin surface and reports on larger tissue volumes in muscle and brain. The near-infrared diffuse optical spectroscopy instrument generate harmless amounts of low-level non-ionizing near-infrared ligh can measure the tissue absorption and scattering properties at depths of 1 cm or more below the skin surface include larger tissue volumes in muscle and brain. The absorption properties of tissue provide and can determine absolute concentrations of deoxygenated hemoglobin, oxygenated hemoglobin, and water, as well as the total hemoglobin saturation. 