A system for monitoring blood flow confined by at least one vessel wall, the system including: at least one implantable diffraction-gratin g transducer being embedded within or adjacent to a vessel wall, the diffraction-grating transducer being suitable for emitting or receiving ultrasound into the blood flow that experiences a measurable Doppler shift indicative of the flow to be measured; and, a source for pulse-exciting the implantable diffraction grating.
