Power velocity integral technique for quantification of flow in valvular heart disease

Abstract

The noninvasive quantification of pathologic backflow, often referred to as regurgitant flow, associated with valvular heart disease has been an elusive medical goal. To date, techniques based on ultrasound have been unsatisfactory due to weak assumptions and indirect estimations. Here, instead, the proposal is to estimate regurgitant flow directly from the Doppler spectrum of the backscattered ultrasound . As backscattered spectral power is hypothesized to be proportional to the sonified blood volume, and spectral frequency is directly related to velocity of flow, the product of power and velocity should be proportional to flow. However, researchers have long assumed the above principles held only for laminar flow, and not for regurgitant jets in which turbulence augments backscatter. Yet as will be demonstrated, the challenge can be surmounted by analyzing the Doppler spectrum at the origin of the regurgitant jet, where flow is laminar since turbulence has not yet developed. Development of a software system that incorporates the theories expounded above, problems encountered using implementation, and their eventual resolution will presently ensue. In the system, power measurements were also calibrated by applying a dual-beam technique, providing absolute values of flow volume. Also presented are in vitro and in vivo data that demonstrate a high degree of accuracy between true flow volume and flow volume measured by the calibratedinte gral of Doppler power times velocity over time (PVTI). Such measurement of turbulent flow volumes directly and noninvasively is unprecedented and overcomes the limitations of current techniques.