Topoflow - A digital full range Doppler velocity meter

A digital implementation of the multigate Doppler blood flowmeter is described. The observation range of 10 cm is divided into 128 depth channels, thus offering the unique possibility of simultaneously recording the blood vessel geometry as well as the blood flow topography, where topography is defined as a two-dimensional map of blood flow velocity along the axis of a blood vessel. The apparatus consists of three major sections: a) Transmitter/receiver and mixer which produce a range phase signal containing the velocity information. b) The range phase signal is sampled, digitized, and stored into 128 memory ceDs for further processing. A feedback circuit significantly reduces the required resolution of the analog to digital converter and at the same time suppresses unwanted low-frequency signals. c) A frequency discriminator yields a voltage proportional to the velocity in each channel. The system can detect SOvelocity profiles per second, sufficient to characterize the pulsatile flow in arteries. The main features of the novel instrument are minimal hardware due to sequential signal processing, ease of operation, and a variety of display modes, including two-dimensional (2D) flow maps. The results, obtained in laboratory tests under simulated conditions as weD as in transcutaneous applications, agree weD with those reported by other investigators using conventional equipment.