Evaluation of Mitral Regurgitation: Comparison of Ultrafast and Focused Ultrasound in an In-Vitro Pulsatile Flow Phantom

Mitral regurgitation (MR) severity is assessed by measuring the regurgitant volume (RVol) with echocardiography using the proximal iso-velocity surface area (PISA) method. The low temporal resolution of focused ultrasound, the assumption of hemispheric iso-velocity contours, and the use of a single point to assess the velocity are the pitfalls of this method. This study evaluates a novel method using ultrafast ultrasound, and multiple points for velocity assessment without the aforementioned geometrical assumption to provide a more accurate RVol measurement. A left heart mock system, comprised of an orifice simulating MR, was filled with water mixed with cellulose. RVols from 20 mL to 70 mL with increments of 10 mL, were delivered by a pulsatile pump which was the reference. Data were acquired at 6000 frames/s by a cardiac phased array probe emitting ultrafast diverging waves, connected to an ultrafast scanner as well as a clinical system emitting focused waves. RVols were computed with the surface integral of the velocity through a planar disk at the input of the orifice with ultrafast transmission (u-PD) and PISA method with focused waves (f-PISA). The error of the two methods was compared. u-PD showed a significant lower error values than f-PISA (18.6 ± 11.5% and 56.5 ± 4.9%, respectively, p < 0.001). This study demonstrates that ultrafast ultrasound can provide accurate multi-point estimates of RVol in a model of MR by leveraging the complete axial velocity mapping at high temporal resolution. Its complementary role to PISA method will be evaluated in future clinical studies.