In efforts to monitor the progression of atherosclerosis using ultrasound, Acoustic Radiation Force Impulse (ARFI¹) and Shear Wave Elasticity Imaging (SWEI²) have been implemented to measure the mechanical stiffness of vascular tissue while colorflow Doppler and spectral Doppler techniques have been used to monitor the associated blood flow hemodynamics.

Towards creating an imaging system capable of collecting both the mechanical and hemodynamic information within one acquisition, a series of combined Bmode/ARFI/Doppler imaging tools were developed. These tools acquire multiple frames of co-registered Bmode echogenicity, ARF induced on-axis displacements and transverse wave velocities, along with blood flow velocity estimates and wall-shear rate (WSR) at frame rates up to 20 Hz over several cardiac cycles. Implemented on a diagnostic ultrasound scanner connected to a laptop for off-line processing, the carotid arteries of patients with and without known carotid artery plaques were scanned.

Processed images were temporally and spatially stable across multiple frames and acquisitions. Cyclic variations across the cardiac cycle were observed, depicting increased vessel wall stiffness and increased WSR during systole compared to diastole. For combined Bmode/ARFI configurations, overall data acquisition and image processing frame rates of 1 Hz were achieved, enabling feedback during the exam. A series of acquired in vivo image sequences will be presented.

Figure 1

Co-registered ARFI displacement image (left) and WSR image (right) shown overlaid on a B-mode image obtained in vivo using a combined B-mode/ARFI/Doppler system.