An optical examination technique employs an optical system for in vivo
non-invasive transcranial examination of brain tissue of a subject. The
optical system includes an optical module arranged for placement on the
exterior of the head, a controller and a processor. The optical module
includes an array of optical input ports and optical detection ports
located in a selected geometrical pattern to provide a multiplicity of
photon migration paths inside the biological tissue. Each optical input
port is constructed to introduce into the examined tissue visible or
infrared light emitted from a light source. Each optical detection port
is constructed to provide light from the tissue to a light detector. The
controller is constructed and arranged to activate one or several light
sources and light detectors so that the light detector detects light that
has migrated over at least one of the photon migration paths. The
processor receives signals corresponding to the detected light and forms
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 of the examined tissue. The processor is
arranged to correlate the first and second data sets to detect abnormal
tissue in the examined tissue.