Ultrasonic Doppler measurement using a pseudo-continuous mode

A pseudo-continuous ultrasound Doppler method was studied theoretically and experimentally. The principle of the method is based on the pulsed-wave mode. Short bursts are emitted with a high pulse repetition frequency, and demodulated echoes are integrated between emitted pulses. Gaps arise in the measurable range due to the lost echoes during emitting time, but a method for partly solving this problem that uses two alternating pulse repetition frequencies was suggested. The proposed pseudo-continuous method is useful for measuring high blood velocities, up to 3.8 m/s, with an emitted frequency of 3.2 MHz, at any depth up to 17 cm. Using the pulsed-wave mode, the maximum measurable velocity under similar conditions would be only 0.6 m/s. Thus, the maximum measurable velocity is six times higher in the pseudo-continuous mode. These results demonstrate the possibility of measuring high blood-flow velocities using a transducer and electronics compatible with the pulsed-wave mode.