Most recently, near infrared (NIR, of wavelength 700-900 nm) optical diffuse spectroscopic imaging has been investigated as a novel diagnostic tool for breast cancer. In the near-infrared (NIR) light spectrum, oxygenated hemoglobin and deoxygenated hemoglobin are the major chromospheres in tissue, and the absorption spectrums of the two hemoglobin states differ across these wavelengths. Thus, there have been many contemporary attempts to use the intra-tissue absorption and scattering of NIR light to quantify functional tissue parameters such as hemoglobin concentration (HbT) and oxygen saturation (StO2), including tumor differentiation within the human breast. To a very good approximation, NIR photons diffuse through relatively thick tissues, such as several centimeters of a human breast. Functional imaging with NIR light offers several novel tissue parameters that differentiate tumors from normal breast tissue. For example, hemoglobin de-saturation in tumors may be increased due to the high oxygen demand of cancers and blood volume may be increased over that of normal background tissue due to the greater vascularization and metabolic needs of cancers.