Ultrasonic time-domain method for sensing fluid flow.

摘要

Pulses of ultrasound are focused in the patient's body to create an interrogation volume where either the magnitude of velocity or the direction of blood flow is to be measured. The strength of the back-scattered signal is measured for each pulse and the mean squared rate of change of the envelope of the range-gated signal is estimated. In order to measure flow velocity independent of direction, the interrogation volume is generated substantially as a sphere by creating an ultrasonic wave envelope in which the components of the mean square spatial gradient are equal in all directions. The estimated mean square rate of change of the envelope of the back-scattered signal is then scaled to provide a direction-independent measurement of flow velocity. In order to determine the direction of flow, the interrogation volume is generated substantially as an ellipsoid. The long axis of the ellipsoidal interrogation volume is then rotated until the measured mean square rate of change of the envelope of the return signal is at a minimum, which is reached when the long axis is aligned with the flow direction. The interrogation volume is preferably rotated and translated using differential phasing of the ultrasonic signals from different transducer elements in a two-dimensional phased array.