Noninvasive methods for measuring myocardial viscoelasticity are needed to assist with evaluation of heart function. The long-term goal of this program is to noninvasively measure and image heart wall mechanical properties with high accuracy and precision. For this purpose, we have developed shear wave dispersion ultrasound vibrometry (SDUV). The availability of noninvasive quantitative heart wall viscoelasticity measurements will support clinical evaluation and population studies. Toward this goal, we have developed: methods to measure shear modulus using MRI (Science 269:1854-1857, 1995), a new imaging method that uses the harmonic vibration of tissue induced by ultrasound radiation pressure (Science 280, 82-85, 1998), theory for harmonic vibration imaging (Proc Natl Acad Sci USA 96:6603-6608, 1999) and a theory for fundamental parameters of radiation pressure (Phys. Rev E 71, 2005). In addition, we developed an inverse solution to this problem using FEM (J Appl Phys 101, 2007). This outstanding record of achievements leads to the following specific goals for the next funding cycle of this program of research: 1) develop advanced theories for solving the very complex inverse problem of determining mechanical properties of the left ventricular myocardium from shear wave properties, 2) use ultrasonic radiation force to induce shear-waves into the heart wall of instrumented open chest and closed chest animals and validate SDUV viscoelastic moduli by independent methods, 3) implement SDUV to characterize the complex shear modulus with high temporal and spatial resolution in closed chest swine with hypertension-induced increased left ventricular/myocardial stiffness and fibrosis, and 4) in hypertensive patients with heart failure and preserved ejection fraction, we will make noninvasive SDUV measurements of myocardial viscoelastic properties, and we will correlate these measurements with catheter-proven increased ventricular/myocardial stiffness and standard echocardiographic measures of diastolic dysfunction. Successful completion of this program will result in a scientific and technological advancement in the field of ultrasonic imaging, providing the cardiologist with a direct quantitative measurement of the regional viscous and elastic compliance of the heart wall. Measurements will be fast enough to be incorporated in the typical cardiac ultrasound examination and allow evaluations at rest and during physiologic or pharmacologic interventions. In this cardiology evaluation of SDUV, we will focus our attention on hypertensive patients with diastolic heart failure as one of the largest populations that may benefit from direct measurements of myocardial viscoelastic properties. We anticipate the technology will provide quantitative measurements of myocardial properties with a wide variety of applications such as ischemic heart disease, cardiomyopathies and heart transplant.
Successful completion of this program will result in a noninvasive, quantitative method for measuring viscoelastic properties of the myocardium that would be a software addition to the current suite of cardiac ultrasound instruments providing the cardiologist with a quantitative measurement of the regional viscous and elastic compliance of the heart wall. Measurements will be fast enough to allow evaluations at rest during routine cardiac ultrasound evaluation as well as during physiologic or pharmacologic interventions.
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