proceedings - International Tissue Elasticity Conference

029 FIRST RESULTS IN THE MEASUREMENT OF RAYLEIGH ELASTICITY PARAMETERS IN
PHANTOMS AND IN–VIVO BREAST TISSUE.
EEW Van Houten 1 , MDJ McGarry 1 , JB Weaver 2 , KD Paulsen 3 .
1 University of Canterbury, Private Bag 4800, Christchurch, New Zealand; 2 Dartmouth Hitchcock
Medical Center, Lebanon, NH 03756, USA, 3 Thayer School of Engineering, Dartmouth College,
Hanover, NH 03755, USA.
Background: The attenuating behavior of soft tissue shows evidence of providing clinical and diagnostic
insight into various soft tissue disorders [1–3]. To make the most of this diagnostic capability,
characterization of the damping behavior of tissue should be as accurate as possible. To date, attenuation
in the case of the time–harmonic tissue behavior found in dynamic elastography has captured the damping
behavior through a single parameter that takes the form of an imaginary component of a complex valued
shear modulus. A more generalized damping formulation for the time–harmonic case, known commonly as
Rayleigh or proportional damping, includes an additional parameter that takes the form of an imaginary
component of a complex valued density. The effects of these two different damping mechanisms can be
shown to be independent across homogeneous distributions and mischaracterization of the damping
structure can be shown to lead to artifacts in the reconstructed attenuation profile [4].
Methods: A novel method for reconstructing the Rayleigh damping distribution of within tissue and
tissue–mimicking phantoms from 3D time–harmonic displacement data obtained via MR imaging has
been developed based on a subzone approach to the global inverse problem [5]. This technique has been
used to evaluate the ability to assess Rayleigh damping distribution from measured data and to initiate
an investigation into the potential clinical value of these measurements.
Results: The two figures below illustrate typical results for this reconstruction method in tissue mimicking
phantoms and breast tissue. It can be seen that that the structure of the various reconstructed mechanical
properties match structural aspects in both cases. Resulting values for real shear modulus and overall
damping levels are in reasonable agreement with values established in the literature or measured by
mechanical testing. The value of real density was fixed at that of water, roughly 1000 kg/m 3 .
42
Figure 1: Rayleigh damping reconstruction from a tissue mimicking heterogeneous phantom.
Figure 2: 3 slices of a Rayleigh damping reconstruction from breast tissue.
Acknowledgements: We gratefully acknowledge support from NIH/NIBIB R01–EB004632–02.
References:
[1] L Huwart et al., Liver Fibrosis: Noninvasive Assessment with MR Elastography versus Aspartate
Aminotransferase–to–Platelet Ratio Index, Radiology, 245, 2007.
[2] R Sinkus et al., Viscoelastic shear properties of in vivo breast lesions measured by MR elastography, J Magn
Reson Imaging, 23(2), 2005.
[3] N Salameh et al., Hepatic viscoelastic parameters measured with MR elastography: correlations with quantitative
analysis of liver fibrosis in the rat, J. Magn Reson Imag, 26(4), 2007.
[4] MDJ McGarry et. al., Reconstructing spatially varying rayleigh damping parameters in magnetic resonance
elastography, Sixth Int Conf Ultrason Meas Imag Tiss Elast, 54, 2007.
[5] M Doyley et al., Steady–state magnetic resonance harmonic elastography: contrast detailed analysis and
preliminary clinical evaluation, First Int Conf Ultrason Meas Imag Tiss Elast, 45, 2002.
indicates Presenter