Noninvasive method for estimation of complex elastic modulus of arterial vessels.

Pulse wave velocity (PWV) is widely used for estimating the stiffness of an artery. It is well-known that a stiffened artery can be associated with various diseases and with aging. Usually, PWV is measured using the "foot-to-foot" method in which the travel time of the wave is measured over a distance. The "foot" of the pressure wave is not clear due to reflected waves and blood noise. Also, PWV is an average indicator of artery stiffness between the two measuring points and, therefore, does not identify local stiffness variations. We propose producing a bending wave in the arterial wall using low-frequency, localized ultrasound radiation force and measuring the wave velocity along the arterial wall. The wave velocity can be measured accurately over a few millimeters. A mathematical model for wave propagation along the artery is developed with which the Young's modulus of the artery can be determined from measured wave velocities. Experiments were conducted on a pig carotid artery cast in a tissue-mimicking gelatin. The wave velocity was measured by the phase change at a known distance for a given frequency. The measured wave velocity is about 3 m/s at 100 Hz and 6.5 m/s at 500 Hz. The real part of complex elastic modulus of the artery is estimated to be 300 kPa.