Simultaneous imaging of artery-wall strain and blood flow realized by high frame rate acquisition of RF echoes

Mechanical properties of the arterial walls are significantly altered by atherosclerosis, and various studies have been recently conducted to measure the regional elastic properties (radial strain) of the arterial wall. We have developed a phasesensitive correlation-based method, namely, the phased-tracking method, to measure the regional radial strain. On the other hand, the measurement of blood flow is an important practical routine in the diagnosis of atherosclerosis. It would be useful if the regional strain of the arterial wall as well as blood flow could be assessed simultaneously. Such measurement would require a high frame rate of several kilohertz. In this study, acquisition of ultrasonic RF echoes at a high frame rate (about 3500 Hz) was achieved using parallel beamforming, in which plane waves were transmitted only three times and receive beamforming created 24 beams for each transmit beam. The accuracy in measurement of the minute radial strain was evaluated by a basic experiment using a cylindrical phantom. The error of the measured strain from the theoretical strain profile and its standard deviation were 4.80/0 and 9.50/0, respectively. Furthermore, the radial strain of a carotid arterial wall and blood flow were simultaneously imaged in vivo.