Principles and design feasibility of a Doppler ultrasound intravascular volumetric flowmeter

A new Doppler ultrasound intravascular method is described for the measurement of volumetric flow. Based on the principles described by C. F. Hottinger and J. D. Meindl (Ultrasonic Imaging, vol. 1, p. 1-15, 1979), it uses a novel semispherical transducer mounted at the tip of a catheter, which generates sample volumes in the form of a thin semispherical shell. Volumetric flow is calculated by using the average velocity determined from the received Doppler spectrum and the area of intersection of a sample volume that completely intersects flow across the vessel. Although a catheter-size transducer was not developed, a larger version was tested using an in vitro steady flow model. Maximum average flow error was limited to 9% for steady flows of 2 to 7 L/min. This error is believed to be a result of the nonuniform intensity generated by the prototype transducer, as well as slight variations in the received power, rather than any fundamental limitations of the flow measurement method itself. Since this study has verified the design principles and feasibility of this new approach, the authors believe that more detailed experimental investigations are warranted.