Flow convergence flow rates from 3-dimensional reconstruction of color Doppler flow maps for computing transvalvular regurgitant flows without geometric assumptions: An in vitro quantitative flow study

Objective: This study was designed to develop and test a 3-dimensional method for direct measurement of flow convergence (FC) region surface area and for quantitating regurgitant flows with an in vitro flow system. Background: Quantitative methods for characterizing regurgitant flow events such as flow convergence with 2-dimensional color flow Doppler imaging systems have yielded variable results and may not be accurate enough to characterize those more complex spatial events. Method: Four differently shaped regurgitant orifices were studied: 3 flat orifices (circular, rectangular, triangular) and a nonflat one mimicking mitral valve prolapse (all 4 orifice areas = 0.24 cm²) in a pulsatile flow model at 8 to 9 different regurgitant flow rates (10 to 50 mL/beat). An ultrasonic flow probe and meter were connected to the flow model to provide reference flow data. Video composite data from the color Doppler flow images of the FC were reconstructed after computer-controlled 180°rotational acquisition was performed. FC surface area (S cm²) was calculated directly without any geometric assumptions by measuring parallel sliced flow convergence arc lengths through the FC volume and multiplying each by the slice thickness (2.5 to 3.2 mm) over 5 to 8 slices and then adding them together. Peak regurgitant flow rate (milliliters per second) was calculated as the product of 3-dimensional determined S (cm²) multiplied by the aliasing velocity (centimeters per second) used for color Doppler imaging. Results: For all of the 4 shaped orifices, there was an excellent relationship between actual peak flow rates and 3-dimensional FC-calculated flow rates with the direct measurement of the surface area of FC (r = 0.99, mean difference = -7.2 to - 0.81 mL/s, % difference = -5% to 0%), whereas a hemielliptic method implemented with 3 axial measurements of the flow convergence zone from 2- dimensional planes underestimated actual flow rate by mean difference = -39.8 to -18.2 mL/s, % difference = -32% to -17% for any given orifice. Conclusions: Three-dimensional reconstruction of flow based on 2-dimensional color Doppler may add quantitative spatial information, especially for complex flow events. Direct measurement of 3-dimensional flow convergence surface areas may improve accuracy for estimation of the severity of valvular regurgitation.