An Interferometric Blood Flow Measurement Technique - A Brief Analysis

An ultrasonic interferometric technique of measuring blood flow with an extravascular probe is presented and analyzed. The difference in phase between pulses of ultrasonic energy transmitted simultaneously from a pair of barium titanate crystals diagonally through the vessel and received by the same pair of crystals is employed as the basic measurement of blood flow velocity. It is shown that the sensitivity is influenced mainly by variability in the internal diameter of the vessel and the zero-flow baseline voltage position is influenced principally by variations in the level of energy reflected from the vessel surfaces. Baseline stability is enhanced by the use of an asymmetrical probe which minimizes the variable reflection components. This measurement technique is currently being employed in long term telemetry implants in which flow measurements have been satisfactorily performed for periods in excess of three months duration.