Right choice is (d) Laser Doppler Blood Flowmeter
Explanation: A system utilizing the Doppler-shift of monochromatic laser light to measure blood flow in the skin is described by Watkins and Holloway (1978). When a laser beam is directed towards the tissue under study, absorption and scattering take place. Radiation scattered in movable structures, such as red cells, is shifted in frequency due to the Doppler effect, while radiation scattered in nonmoving soft tissue is unshifted in frequency.