Noninvasive assessment of wall-shear rate and vascular elasticity using combined ARFI/SWEI/spectral Doppler imaging system.

The progression of atherosclerotic disease is a complex process believed to be a function of the localized mechanical properties and hemodynamic loading associated with the arterial wall. It is hypothesized that measurements of cardiovascular stiffness and wall-shear rate (WSR) may provide important information regarding vascular remodeling, endothelial function and the growth of soft lipid-filled plaques that could help a clinician better predict the occurrence of clinical events such as stroke. Two novel ARFI based imaging techniques, combined on-axis/off-axis ARFI/Spectral Doppler Imaging (SAD-SWEI) and Gated 2D ARFI/Spectral Doppler Imaging (SAD-Gated), were developed to form co-registered depictions of B-mode echogenicity, ARFI displacements, ARF-excited transverse wave velocity estimates and estimates ofwall-shear rate throughout the cardiac cycle. Implemented on a commercial ultrasound scanner, the developed techniques were evaluated in tissue-mimicking and steady-state flow phantoms and compared with conventional techniques, other published study results and theoretical values. Initial in vivo feasibility of the method is demonstrated with results obtained from scanning the carotid arteries of five healthy volunteers. Cyclic variations over the cardiac cycle were observed in on-axis displacements, off-axis transverse-wave velocities and wall-shear rates.