The method involves measuring the velocity of blood cells at right angles to the tissue surface. The laser beam pref. has a point diameter of the order of 10 micrometre, and the reflected light is captured using a camera (3) in conjunction with a lens system and beam splitters (BS1/F1;BS2). The lens system (L2) receives the back-scattered laser beam and focusses it the Doppler shifted radiation via the beam splitters onto a photoreceiver (5). The lens system also focuses the light that is backscattered by the surrounding tissue and non-Doppler shifted.
