Transcutaneous Blood Flow Measurements Using Pseudorandom Noise Doppler System

In order to obviate the limitations of the conventional coherent ultrasonic Doppler flowmeters we have developed a new device. In this apparatus the continuous wave is replaced by a pseudorandom signal. We show, both theoretically (Waag et al. [12]) and experimentally, that the pseudorandom system offers advantages. The most important result concerns the improvement of the signal-to-noise ratio which can be as large as 20 dB. Furthermore, it is possible to decrease the frequency and the distance ambiguity by a factor of two. Compared to the "random noise flowmeter" (Newhouse et al. [7], Jethwa et al. [5]) our system measures flow near the wall of vessels or in ultrasonic field in which there are important fixed echoes. To illustrate the feasibility of this new device, we show some results obtained by the transcutaneous method.