On increasing the range of pulsed Doppler systems for blood flow measurement.

TLDR: This technique which is easily applicable to existing pulsed Dopplers, should extend the clinical applicability of these systems to long range or high velocity flows whose Doppler spectra are sufficiently narrow.

Abstract: Existing pulsed Dopplers have a fundamental limitation which makes them unable to measure a velocity v at a range R greater than that given by the limit Rv = c 2 /8 φ 0 where c is the sound velocity and f 0 the transmitted ultrasound frequency. This limit makes it impossible for conventional pulsed Dopplers to measure blood velocity transcutaneously in such locations as stenosed or regurgitant heart valves in adults. This paper described a principle using periodic changes of the repetition frequency of the transmitted signal. This increases the range limit of pulsed Doppler systems by the ratio of the Doppler spectrum enter frequency to its bandwidth. This technique which is easily applicable to existing pulsed Dopplers, should extend the clinical applicability of these systems to long range or high velocity flows whose Doppler spectra are sufficiently narrow