A probe and an apparatus for cerebral diagnostics and therapy, in particular for measuring absolute values of regional cerebral flow (CBF) and cerebral oxygenation. The probe is inserted through a burr hole in the skull and comprises illuminating device, light receiving device and a coating encapsulating said illuminating device and said light receiving means. The coating has a longitudinal shape and is adapted to fit through a burr hole in the skull. The coating is further adapted to slide between the skull and the dura, to be inserted into the ventricular system, and/or to be inserted into the cerebral tissue.