An ultrasonic fluctuation velocimeter.

A novel ultrasonic velocimeter is described and evaluated with a view to measuring blood flow in vivo. The device is not based on the Doppler principle but operates by analysing the random fluctuations of the echo backscattered by blood. The rate at which the amplitude of the reflected signal passes through its mean level is related (by the dimensions of the resolution cell) to the velocity of the scatterers. Experimental trials in vitro validate the concept although there is a factor of two disagreement with predictions. The device is compared with the conventional Doppler volocimeter and problems on operation in vivo are discussed.