1. An optical system for in vivo, non-invasive examination of breast tissue of a female subject comprising: at least one light source constructed to emit visible or infrared light and at least one 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, said optical input ports being constructed to introduce visible or infrared light emitted from said at least one light source, said optical detection ports 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 at least one light detector; a controller constructed and arranged to control operation of said at least one light source and said at least one 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 at least one light detector and programmed to form at least two data sets, wherein each data value of said at least two data sets corresponds to said detected light for a pair of said input and said detection ports, 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 programmed to calculate spatial congruence of said first and second data sets by calculating a maximum value of a difference between said blood volume and oxygenation data divided by a maximum normalized value to detect abnormal tissue in the examined tissue region.