Measurement of longitudinal and circumferential waves in tubes and artery excited with ultrasound radiation force

Abstract

Increased arterial stiffness is associated with increased risk of cardiovascular events. Radiation force methods have been developed to investigate the longitudinal wave speeds of the artery with high spatial and temporal resolution. The artery is anisotropic so to fully characterize its material properties, we need to examine longitudinal and circumferential wave speeds. We used ultrasound radiation force to generate propagating waves in the wall of rubber tubes and an excised pig carotid artery and measured the wave motion using compounded plane wave imaging. To study the tubes we used two Verasonics systems equipped with linear array transducers. The transducers were placed 90° with respect to each other to obtain different views along the tube wall. One transducer applied a radiation force push and then both systems were used to detect the wall motion of the tube. One system was used for the artery experiment. The group velocity of the longitudinal wave, c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> , was measured along the length of the vessel/tube. The motion near the radiation force push location was analyzed to measure the speed of the circumferential wave. We varied the transmural pressure over ranges of 10-30 mmHg and 20-200 mmHg for the tubes and artery, respectively. We confirmed the presence of circumferential waves by pushing on a tube with one transducer and measuring with the other transducer at 90°. We compared c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> and c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in the tubes and found very good agreement in tube 1 and a bias in tube 2. It was expected that both wave speeds would be similar because the material is isotropic. The c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> and c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values for the artery show similar trends but the c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> values are lower than the c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> values. We were able to measure values of c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> and c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in tubes and arteries. The speeds measured in isotropic tubes were similar. The values of c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> in an excised artery were shown to be lower than the values of c <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">l</sub> .