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Requirements for accurate estimation of anisotropic material parameters by magnetic resonance elastography: A computational study.

ABSTRACT: To establish the essential requirements for characterization of a transversely isotropic material by magnetic resonance elastography (MRE).Three methods for characterizing nearly incompressible, transversely isotropic (ITI) materials were used to analyze data from closed-form expressions for traveling waves, finite-element (FE) simulations of waves in homogeneous ITI material, and FE simulations of waves in heterogeneous material. Key properties are the complex shear modulus ?2 , shear anisotropy ?=?1/?2-1, and tensile anisotropy ?=E1/E2-1.Each method provided good estimates of ITI parameters when both slow and fast shear waves with multiple propagation directions were present. No method gave accurate estimates when the displacement field contained only slow shear waves, only fast shear waves, or waves with only a single propagation direction. Methods based on directional filtering are robust to noise and include explicit checks of propagation and polarization. Curl-based methods led to more accurate estimates in low noise conditions. Parameter estimation in heterogeneous materials is challenging for all methods.Multiple shear waves, both slow and fast, with different propagation directions, must be present in the displacement field for accurate parameter estimates in ITI materials. Experimental design and data analysis can ensure that these requirements are met. Magn Reson Med 78:2360-2372, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

SUBMITTER: Tweten DJ

PROVIDER: S-EPMC5513802 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Requirements for accurate estimation of anisotropic material parameters by magnetic resonance elastography: A computational study.

Tweten D J DJ Okamoto R J RJ Bayly P V PV

Magnetic resonance in medicine 20170117 6

<h4>Purpose</h4>To establish the essential requirements for characterization of a transversely isotropic material by magnetic resonance elastography (MRE).<h4>Theory and methods</h4>Three methods for characterizing nearly incompressible, transversely isotropic (ITI) materials were used to analyze data from closed-form expressions for traveling waves, finite-element (FE) simulations of waves in homogeneous ITI material, and FE simulations of waves in heterogeneous material. Key properties are the ...[more]

PMID: 28097687

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Project description:BACKGROUND AND OBJECTIVES:Fibrosis is a major cause of kidney allograft injury. Currently, the only means of assessing allograft fibrosis is by biopsy, an invasive procedure that samples <1% of the kidney. We examined whether magnetic resonance elastography, an imaging-based measure of organ stiffness, could noninvasively estimate allograft fibrosis and predict progression of allograft dysfunction. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS:Kidney allograft recipients >1 year post-transplant undergoing an allograft biopsy first underwent free-breathing, flow-compensated magnetic resonance elastography on a 3.0-T magnetic resonance imaging scanner. Each patient had serial eGFR measurements after the elastography scan for a follow-up period of up to 1 year. The mean stiffness value of the kidney allograft was compared with both the histopathologic Banff fibrosis score and the rate of eGFR change during the follow-up period. RESULTS:Sixteen patients who underwent magnetic resonance elastography and biopsy were studied (mean age: 54±9 years old). Whole-kidney mean stiffness ranged between 3.5 and 7.3 kPa. Whole-kidney stiffness correlated with biopsy-derived Banff fibrosis score (Spearman rho =0.67; P<0.01). Stiffness was heterogeneously distributed within each kidney, providing a possible explanation for the lack of a stronger stiffness-fibrosis correlation. We also found negative correlations between whole-kidney stiffness and both baseline eGFR (Spearman rho =-0.65; P<0.01) and eGFR change over time (Spearman rho =-0.70; P<0.01). Irrespective of the baseline eGFR, increased kidney stiffness was associated with a greater eGFR decline (regression r2=0.48; P=0.03). CONCLUSIONS:Given the limitations of allograft biopsy, our pilot study suggests the potential for magnetic resonance elastography as a novel noninvasive measure of whole-allograft fibrosis burden that may predict future changes in kidney function. Future studies exploring the utility and accuracy of magnetic resonance elastography are needed.

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Requirements for accurate estimation of anisotropic material parameters by magnetic resonance elastography: A computational study.

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Requirements for accurate estimation of anisotropic material parameters by magnetic resonance elastography: A computational study.

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