A Self-Correcting, Phase-Locked Tracking Method for Pulsed Ultrasound

A tracking system for pulsed ultrasound was developed with the specific aim of overcoming some of the limitations inherent in both amplitude-discrimination and phase-locked tracking techniques. The tracking accuracy in amplitude-discrimination systems is tied to the amplitude stability of the first cycle of the ultrasonic wavefront. Phase-locked systems cannot distinguish the leading edge of the ultrasonic wavefront and once unlocked are unable to realign the tracking gate with the same cycle of the ultrasonic tone burst. The tracking system described offers automatic alignment with the leading edge of a pulsed ultrasonic signal, yet can ignore fluctuations in amplitude so long as any one cycle of the received ultrasonic tone burst remains above ambient noise levels. A prototype myocardial dimensioning system which employs this tracking method has been built and is in use at the Department of Medicine, Cardiovascular Division, University of California at San Francisco.