Geometry of the diffuse optical spectroscopy linescan, demonstrating (a) measurement locations and (b) overall probe orientation on the breast. The handheld probe was moved along a linear grid of steps spaced 10 mm apart. Both the tumor region (which had been previously identified) as well as the contra-lateral normal side were measured. Note that the orientation, location, and number of points of the linescan varied with the clinical presentation of the lesion. In (b) we demonstrate the diffusive nature of near infrared photons in tissue.