Evaluation of mitral regurgitation using ultrafast ultrasound: in vitro validation in a pulsatile flow phantom

Abstract Introduction The regurgitant volume (RVol) is used to decide which patient with mitral valve regurgitation (MR) needs to be referred to invasive therapeutic procedure. It is currently computed with the proximal isovelocity surface area (PISA, fig. 1a) method which uses a single velocity value at the aliasing point (fig. 1b). The RVol is then obtained by integrating all the PISA over time. This method used in the clinic with focused echocardiography is known to underestimate the RVol [1]. Ultrafast ultrasound color Doppler can map the flow field of interest at any point in the field of view with high temporal and spatial resolution. In this study, we investigated whether we can improve the precision of the RVol quantification with ultrafast ultrasound with respect to the clinical standard PISA method. Methods In a left heart phantom, different physiological RVols were delivered by a pulsatile pump through a regurgitant orifice. Data were acquired at 6000 frames/s by a conventional cardiac phased array probe (central frequency at 2.75MHz) emitting ultrafast diverging waves, connected to an ultrafast scanner. Power Doppler was first computed to select the area of the image with higher signal (fig. 1c). Color Doppler mapping (fig. 1d) was computed over the systolic phase. A point on the central line in the axis of the orifice was selected in in the convergence zone were the mean velocity was 0.25m/s on average. On this point, RVols were computed as the surface integral of the velocity through a planar disk at the input of the orifice and was integrated over the systolic phase (blue dotted line, fig. 1e) and with the PISA method at this same point (red point fig 1e). The accuracy of the 2 methods were compared by computing the difference in their mean absolute value and percentage. Results RVol estimation using planar disk method yielded statistically significant lower absolute values than the clinical standard PISA method (9±8ml vs 31±10 ml, p