Arterial Properties From Stimulated Acoustical Emission
A simple and robust method to measure anisotropic arterial wall viscoelasticity can help assist researchers in understanding new targets in the arterial wall. Estimation of the material properties of the arterial wall creates a very complex problem because of the complexity of the wall itself. To approach this problem, the lab has designed a four-component program of investigation.
The first part of the program is designed to complete the mathematical and computational foundations to support newly developed methods of estimating anisotropic and viscoelastic material properties from measurable arterial wall responses to applied radiation force. This covers computation of the radiation stress from the ultrasound beams and includes two approaches to solving the inverse problem (for example, an analytic computational inverse method and an iterative inverse finite element method).
The second part of the program is designed to give laboratory-based validation of the methods developed in part one. The validation is conducted on excised arteries and tubes. In addition, the dependence of the material properties on various constituents of the artery, such as elastin and collagen, is determined.
The third part tests the implementation of the developed methods in live pigs. The point is to test the methods in pig arteries that have a wide range of stiffness induced by disease — in this case, induced hypertension. Histomorphometry is done on the arteries and correlated with the measured viscoelastic moduli of the arterial walls.
The fourth part implements the clinical application of these methods. To do this, measurements are made of the anisotropic viscoelastic moduli of arteries in humans that are already enrolled in ongoing clinical studies. Classical arterial stiffness measurements, such as pulse wave velocity and augmentation index, and pulse pressure is correlated to the viscoelastic arterial wall moduli measured with the new system. Implementation in a clinical scanner of the methods developed here allows for measuring humans using a portable scanner that can be added to funding for the National Institutes of Health clinical trials with minimal modification of the ongoing protocols and minimal cost.
Successful completion of these studies will result in knowledge of the relationship of the viscoelastic arterial wall moduli to an array of clinical attributes in the studied populations, resulting in a valuable clinical ultrasound tool.