Evaluation of local arterial stiffness using ultrafast imaging: A comparative study using local arterial pulse wave velocity estimation and shear wave imaging

We have previously proposed a novel method for measuring arterial stiffness using shear wave imaging (SWI). In this study, we evaluate the performance of this method on a healthy population (N=30) and we compare it to local measurement of the arterial pulse wave velocity (PWV) achieved at the same arterial site using ultrafast imaging. Ultrafast imaging was used to track shear wave induced remotely by acoustic radiation force at the carotid site at a frame rate of 10000 images/second with a 8 MHz ultrasound probe. SWI was acquired with a repetition rate of 7 Hz in order to measure stiffness variation over the cardiac cycle. The axial-velocity field in the imaging plane was obtained using conventional Doppler algorithm. As shown in a previous study, acoustic radiation force applied normally to the arterial wall induces mainly a flexural guided mode (FO) which propagates between 100 to 1500 Hz. The dispersion curve of this mode is extracted from the 2D-FFT of the shear wave spatio-temporal velocity field within and along the arterial wall. The shear modulus is then estimated by a theoretical fit of the experimental dispersion curve. Ultrafast imaging was also used to measure the tissue velocity of the arterial wall at the same site at a frame rate of 1000 images/s during 1 second. PWV was estimated by tracking the pulse wave along the arterial wall based on spatio-temporal velocity field at early and end-systole. Each ultrasound measurement was repeated 3 times on each carotid to estimate the reproducibility of the technique. Lower reproducibility was found on systolic PWV measurements. Thanks to its higher frequency content, the PWV at end-systole was measured more accurately and was found to be more reliable, but was not visible in all volunteers. In contrast, SWI offered high reproducibility. Moreover, arterial stiffness was achieved 6 times per seconds contrary to one time per second for PWV, giving access to the arterial stiffness time variation during the cardiac cycle.