Arterial Properties from Stimulated Acoustical Emission

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DESCRIPTION (provided by applicant): Increased stiffness of the great vessels and conducting arteries has recently gained acceptance as a potential risk factor for cardiovascular and many other diseases. Standard methods for estimating blood vessel stiffness in humans measure changes in blood vessel diameter and relate these measurements to arterial pressure to estimate arterial stiffness (compliance). This technique can be time-consuming, is difficult to apply during physiologic maneuvers associated with rapid changes in blood vessel tone, and there is controversy about which of several derived calculations of stiffness is best. In addition, non-invasive determination of blood pressure may bring additional errors in the estimation of arterial stiffness. Therefore, development of new approaches to assess blood vessel stiffness in humans has the potential to be an extremely useful tool in studying human cardiovascular function in health and disease. The advantages of the methods proposed here are that they are noninvasive and fast allowing real-time measurement of properties, and they take into account the fact that properties are a function of frequency. Our new method is an extension of our vibro-acoustography technique. We use radiation pressure of focused ultrasound beams to vibrate the wall of a vessel at a set of low frequencies (50-600 Hz). We then measure the speed and attenuation of the resulting propagating shear wave within the vessel wall for each frequency. The Young's modulus is then calculated from the dispersion curves. The goal of this application is to develop this noninvasive method for quantitatively measuring the material properties of vessels. We will achieve these goals with four specific aims including: 1) Extended development of advanced wave propagation theory for shear waves in walls of vessels and for acoustic emission from the waves, 2) Development of better transducers for inducing tissue motion and receivers for measuring the resulting acoustic emission and displacement, 3) Validation of our newly developed vibrometry methods in animals, and 4) Application of vibrometry methods to quantitative measurement of vessel wall viscoelasticity (complex Young's modulus) in humans. Successful completion of this program will result in new noninvasive methods to assess arterial stiffness and other material properties with fast and accurate measurements applicable to the conscious human.