1. An optical system for in vivo, non-invasive examination of breast tissue of a female subject comprising: a light source and a light detector, an optical module including an array of optical input ports and detection ports located in a selected geometrical pattern to provide a multiplicity of photon migration paths inside an examined region of breast tissue, each said optical input port being constructed to introduce visible or infrared light emitted from said light source, each said optical detection port being constructed to receive photons of light that have migrated in the examined tissue region from at least one of said input ports and provide said received light to said light detector; a controller constructed and arranged to control operation of said light source and said light detector to detect light that has migrated over at least one of said photon migration paths; and a processor connected to receive signals from said detector and arranged to form at least two data sets, a first of said data sets representing blood volume in the examined tissue region and a second of said data sets representing blood oxygenation in the examined tissue region; said processor being arranged to calculate congruence of said first and second data sets to detect abnormal tissue in the examined tissue region.