Ultrasound Imaging - James F. Greenleaf

Multidimensional Heart Imaging With Ultrasound

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, researchers have developed shear wave dispersion ultrasound vibrometry (SDUV) techniques. The availability of noninvasive quantitative heart wall viscoelasticity measurements will support clinical evaluation and population studies.

Toward this objective, the following has been developed:

• Methods to measure shear modulus using magnetic resonance imaging
• New imaging methods that use the harmonic vibration of tissue induced by ultrasound radiation pressure
• Theory for harmonic vibration imaging
• Theory for fundamental parameters of radiation pressure
• Development of an inverse solution to this problem using finite element solution

Project aims

The outstanding record of achievements leads to the following specific goals for the next funding cycle of this program of research:

• Develop advanced theories for solving the very complex inverse problem of determining mechanical properties of the left ventricular myocardium from shear wave properties.
• 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.
• Implement SDUV to characterize the complex shear modulus with high temporal and spatial resolution in closed-chest swine with hypertension-induced increased left ventricular or myocardial stiffness and fibrosis.
• Make noninvasive SDUV measurements of myocardial viscoelastic properties in hypertensive patients with heart failure and preserved ejection fraction. Researchers will correlate these measurements with catheter-proven increased ventricular or 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 incorporate them in the typical cardiac ultrasound examination and allow evaluations at rest and during physiologic or pharmacologic interventions.

In this cardiology evaluation of SDUV, researcher will focus attention on hypertensive patients with diastolic heart failure — one of the largest populations that may benefit from direct measurements of myocardial viscoelastic properties. The lab anticipates the technology will provide quantitative measurements of myocardial properties with a wide variety of applications, such as ischemic heart disease, cardiomyopathies and heart transplant.

References

Brigham JC, Aquino W, Mitri FG, Greenleaf JF, Fatemi M. Inverse estimation of viscoelastic material properties for solids immersed in fluids using vibroacoustic techniques. Journal of Applied Physics. 2007;101:023509.

Fatemi M, Greenleaf JF. Ultrasound-stimulated vibro-acoustic spectrography. Science. 1998;280:82.

Fatemi M, Greenleaf JF. Vibro-acoustography: An imaging modality based on ultrasound-stimulated acoustic emission. Proceedings of the National Academy of Sciences of the United States of America. 1999;96:6603.

Mitri FG, Chen S. Theory of dynamic acoustic radiation force experienced by solid cylinders. Physical Review E — Statistical, Nonlinear, and Soft Matter Physics. 2005;71:016306.

Muthupillai R, Lomas DJ, Rossman PJ, Greenleaf JF, Manduca A, Ehman RL. Magnetic resonance elastography by direct visualization of propagating acoustic strain waves. Science. 1995;269:1854.