Flow quantification in valvular heart disease based on the integral of backscattered acoustic power using Doppler ultrasound

The noninvasive quantification of pathologic backflow, 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, we propose to estimate regurgitant flow directly from the Doppler spectrum of the backscattered ultrasound. Since backscattered spectral power is proportional to the sonified blood volume and spectral frequency is directly related to velocity, power times velocity should be proportional to flow. To date, however investigators have assumed this held only for laminar flow, not for regurgitant jets in which turbulence augments backscatter. We demonstrate that this challenge can be overcome by analyzing the Doppler spectrum at the origin of the regurgitant jet, where flow is laminar since turbulence has not yet developed. We present in vitro and in vivo data that demonstrate that there is a linear proportionality between regurgitant flow and the integral of Doppler power times velocity (PVI). Power measurements were also calibrated by applying a dual-beam technique, providing absolute values of flow rate and volume in vivo. In our work we demonstrate that in patients with valvular heart disease, this new PVI technique allows for the measurement of regurgitant flow directly and noninvasively for the first time, overcoming the limitations of current techniques.