Noninvasive Estimation of Pressure Changes Using 2-D Vector Velocity Ultrasound: An Experimental Study With In Vivo...

A noninvasive method for estimating intravascular pressure changes using 2-D vector velocity is presented. The method was first validated on computational fluid dynamic (CFD) data and with catheter measurements on phantoms. Hereafter, the method was tested in vivo at the carotid bifurcation and at the aortic valve of two healthy volunteers. Ultrasound measurements were performed using the experimental scanner SARUS, in combination with an 8 MHz linear array transducer for experimental scans and a carotid scan, whereas a 3.5-MHz phased array probe was employed for a scan of an aortic valve. Measured 2-D fields of angle-independent vector velocities were obtained using synthetic aperture imaging. Pressure drops from simulated steady flow through six vessel geometries spanning different degrees of diameter narrowing, running from 20%-70%, showed relative biases from 0.35% to 12.06%, depending on the degree of constriction. Phantom measurements were performed on a vessel with the same geometry as the 70% constricted CFD model. The derived pressure drops were compared to pressure drops measured by a clinically used 4F catheter and to a finite-element model. The proposed method showed peak systolic pressure drops of -3 kPa ± 57 Pa, while the catheter and the simulation model showed -5.4 kPa ± 52 Pa and -2.9 kPa, respectively. An in vivo acquisition of 10 s was made at the carotid bifurcation. This produced eight cardiac cycles from where pressure gradients of -227 ± 15 Pa were found. Finally, the aortic valve measurement showed a peak pressure drop of -2.1 kPa over one cardiac cycle. In conclusion, pressure gradients from convective flow changes are detectable using 2-D vector velocity ultrasound.