FRIDAY MORNING, 20 MAY 2005 REGENCY E, 8:30 A.M. TO 12:00 ...

9:20
5aBBb4. Shear wave interferometry, an application of sonoelastography. Clark Z. Wu and Kevin J. Parker Hopeman 204 ECE
Dept., Univ. of Rochester, Rochester, NY 14623, wuzhe@ece.rochester.edu
Sonoelastography is an ultrasound imaging technique where low-amplitude, low-frequency LF vibration is detected and displayed
via real-time Doppler techniques. When multiple coherent shear wave sources exist, shear wave interference patterns appear.
Two shear wave sources at the same frequency create hyperbolic shaped interference patterns in homogeneous, isotropic elastic media.
Shear wave speed can be estimated from the fringe separation and the source frequency. If the two sources are driven at slightly
different sinusoidal frequencies, the interference patterns no longer remain stationary. It is proven that the apparent velocity of the
fringes is approximately proportional to the local shear wave velocity. With this approach, local shear wave speed in elastic media can
be estimated. In addition, with a single shear wave source at frequency f and the ultrasound probe externally vibrated at frequency
f f , a novel type of moving interference between the shear waves and the frame of reference motion is created. The moving
interference fringes represent the shape of shear wave wavefronts while traveling at a much slower speed. This approach provides a
real-time visualization of shear wave propagation and local wave speed estimation from which local stiffness is inferred. Work
supported by NIH.
9:45
5aBBb5. Magnetic resonance elastography. Richard Ehman and Armando Manduca Depts. of Radiol. and Bioengineering, Mayo
Clinic, Rochester, MN 55905
The goal of our research is to develop MRI-based methods for assessing the mechanical properties of tissues in vivo. We have
focused on a novel MRI technique for visualizing propagating acoustic shear waves Science 269, 1854–1857 1995. Suitable
dynamic shear stress for Magnetic Resonance Elastography MRE can be generated by surface drivers, inertial effects, acoustic
radiation pressure, or endogenous physiologic mechanisms. The MRE acquisition sequence is capable of visualizing cyclic tissue
motion of less than 1 micron in displacement amplitude, with imaging times ranging from 100 ms to several minutes. Inversion
algorithms based on continuum mechanics are used to process the acquired data to generate maps of mechanical properties such as
depict stiffness, viscosity, attenuation, and anisotropic behavior. We have applied MRE to assess specimens of a variety of tissues,
ranging in stiffness from lung to cartilage. Human studies have demonstrated that it is feasible to apply MRE to quantitatively image
the mechanical properties of skeletal muscles, gray and white matter in the brain, thyroid, kidney, liver, and skin. Our preliminary
clinical studies have to date applied MRE to observe changes in tissue mechanical properties in patients with breast, brain, and thyroid
tumors, liver fibrosis, and diffuse diseases of skeletal muscle.
10:10–10:25 Break
Contributed Papers
10:25
5aBBb6. Microscopic dynamic magnetic resonance elastography.
Shadi F. Othman, Thomas J. Royston, and Richard L. Magin Univ. of
Illinois at Chicago, 842 W. Taylor St. MC 251, Chicago, IL 60607
Microscopic magnetic resonance elastography uMRE is a high resolution
imaging technique for measuring the viscoelastic properties of small
synthetic and biological samples. Mechanical shear waves, typically with
amplitudes of less than 100 m and frequencies of 500–600 Hz, are induced
using a piezoelectric oscillator directly coupled to the region of
interest. By using multiple phase offsets and motion encoding gradients
we acquire data that allows the generation of images that depict shear
wave motion and the calculation of local values of the tissue viscoelastic
properties. Recent MRE investigations are increasingly being conducted at
higher spatial resolution to establish histological correlations between
elasticity maps and tissue structures; such microscopic MRE studies require
stronger static fields, stronger magnetic field gradients, higher performance
RF coils, and more compact, higher frequency mechanical actuators.
Microscopic MRE experiments were conducted at 11.74 T in a 54
mm diameter vertical bore magnet with a 10 mm diameter25 mm length
cylindrical space available for imaging. The field-of-view ranged from 4 to
14 mm. The study was conducted on agarose gel phantoms of different
concentrations ranging from 025%–1% w. Different biological samples,
including frog oocytes and tissue engineered constructs, were also tested.
10:40
5aBBb7. Coupled vibration and sound radiation from a fluid-filled
and submerged or embedded vascular tube with internal turbulent
flow due to a constriction. Yigit Yazicioglu, Thomas J. Royston, Todd
Spohnholtz, Bryn Martin Univ. of Illinois at Chicago, 842 W. Taylor St.
MC 251, Chicago, IL 60607, Francis Loth Univ. of Illinois at Chicago,
Chicago, IL 60607, and Hisham Bassiouny Univ. of Chicago, Chicago,
IL 60637
The vibration of a thin-walled cylindrical, compliant viscoelastic tube
with internal flow and an axisymmetric constriction that results in turbulent
fluid flow is studied theoretically and experimentally. Vibration of the
tube is considered with internal fluid-coupling only and with coupling to
internal flowing fluid and external stagnant fluid or external tissue-like
viscoelastic material. The theoretical analysis includes the adaptation of a
model for turbulence in the internal fluid and its vibratory excitation of
and interaction with the tube wall and surrounding viscoelastic medium.
Theoretical predictions are compared with experimental measurements
conducted on a flow model system using laser Doppler vibrometry to
measure tube vibration and the vibration of the surrounding viscoelastic
medium, as well as miniature hydrophones to measure fluid pressure in the
tube. Discrepancies between theory and experiment and the coupled nature
of the fluid-structure interaction are highlighted. This study is relevant to
and may provide further incite into vascular patency and mechanisms of
5a FRI. AM
2587 J. Acoust. Soc. Am., Vol. 117, No. 4, Pt. 2, April 2005 149th Meeting: Acoustical Society of America 2587