Modeling shear modulus distribution in magnetic resonance elastography with piecewise constant level sets

2012 ◽  
Vol 30 (3) ◽  
pp. 390-401 ◽  
Author(s):  
Bing Nan Li ◽  
Chee Kong Chui ◽  
Sim Heng Ong ◽  
Tomokazu Numano ◽  
Toshikatsu Washio ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Level Sets ◽  
Magnetic Resonance Elastography ◽  
Constant Level ◽  
Piecewise Constant

Magnetic Resonance Elastography for the Measurement of Annulus Fibrosus Material Properties

2011 ◽  
Author(s):  
Daniel H. Cortes ◽  
Lachlan J. Smith ◽  
Sung M. Moon ◽  
Jeremy F. Magland ◽  
Alexander C. Wright ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Magnetic Resonance ◽  
Shear Modulus ◽  
Disc Degeneration ◽  
Annulus Fibrosus ◽  
Pulse Sequence ◽  
Imaging Techniques ◽  
Mechanical Vibration ◽  
Magnetic Resonance Elastography

Intervertebral disc degeneration is characterized by a progressive cascade of structural, biochemical and biomechanical changes affecting the annulus fibrosus (AF), nucleus pulposus (NP) and end plates (EP). These changes are considered to contribute to the onset of back pain. It has been shown that mechanical properties of the AF and NP change significantly with degeneration [1,2]. Therefore, mechanical properties have the potential to serve as a biomarker for diagnosis of disc degeneration. Currently, disc degeneration is diagnosed based on the detection of structural and compositional changes using MRI, X-ray, discography and other imaging techniques. These methods, however, do not measure directly the mechanical properties of the extracellular matrix of the disc. Magnetic Resonance Elastography (MRE) is a technique that has been used to measure in vivo mechanical properties of soft tissue by applying a mechanical vibration and measuring displacements with a motion-sensitized MRI pulse sequence [3]. The mechanical properties (e.g., the shear modulus) are calculated from the displacement field using an inverse method. Since the applied displacements are in the order of few microns, fibers may not be stretched enough to remove crimping. Therefore, it is unknown if the anisotropy of the AF due to the contribution of the fibers is detectable using MRE. The objective of this study is twofold: to measure shear properties of AF in different orientations to determine the degree of AF anisotropy observable by MRE, and to identify the contribution of different AF constituents to the measured shear modulus by applying different biochemical treatments.

Validation of Magnetic Resonance Elastography by Dynamic Shear Testing in the Shear Wave Regime

2010 ◽  
Author(s):  
Ruth J. Okamoto ◽  
Erik H. Clayton ◽  
Kate S. Wilson ◽  
Philip V. Bayly
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Shear Wave ◽  
Shear Force ◽  
Magnetic Resonance Elastography ◽  
Dynamic Shear ◽  
Complex Shear Modulus ◽  
Shear Testing ◽  
Complex Shear ◽  
Propagating Shear

Magnetic resonance elastography (MRE) is a novel experimental technique for probing the dynamic shear modulus of soft biological tissue non-invasively and in vivo. MRE utilizes a standard MRI scanner to acquire images of propagating shear waves through a specimen that is subject to external harmonic mechanical actuation; commonly at frequencies in excess of 200Hz. At steady state, the wavelength of the propagating shear wave can be used to estimate the shear modulus of the tissue. Dynamic shear testing (DST) is also used to characterize soft biomaterials. Thin samples of the material are subject to oscillatory shear strains. Shear force is measured, and converted to shear stress — analysis of this data of a range of frequencies gives a complex shear modulus. The data analysis method assumes that the shear displacement is linear and shear strain is constant through the thickness of the sample. In soft tissues, very thin samples are typically used to avoid inertial effects at higher frequencies. As the thickness of the sample decreases, it is more difficult to cut samples of uniform thickness and to maintain structural integrity of the sample. Thus in practice, measurements of brain tissue properties using DST without inertial correction are limited to low frequencies. In this work, we bridge the frequency regimes of DST and MRE by testing thick samples using DST over a range of frequencies that generates a shear wave in the sample, with a corresponding peak in the measured shear force. The frequency and magnitude of this peak give additional information about the complex shear modulus of the material being tested, and these DST results are interpreted using a finite element (FE) model of the sample. Using this method, we can obtain an estimate of shear modulus in an intermediate frequency regime between that of standard DST and MRE.

scholarly journals Shear Modulus Decomposition Algorithm in Magnetic Resonance Elastography

2009 ◽  
Vol 28 (10) ◽  
pp. 1526-1533 ◽  
Author(s):  
Oh In Kwon ◽  
Chunjae Park ◽  
Hyun Soo Nam ◽  
Eung Je Woo ◽  
Jin Keun Seo ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Magnetic Resonance Elastography ◽  
Decomposition Algorithm

scholarly journals Feasibility of Using Magnetic Resonance Elastography to Study the Effect of Aging on Shear Modulus of Skeletal Muscle

2009 ◽  
Vol 25 (1) ◽  
pp. 93-97 ◽  
Author(s):  
Zachary J. Domire ◽  
Matthew B. McCullough ◽  
Qingshan Chen ◽  
Kai-Nan An
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Significant Relationship ◽  
Skeletal Muscles ◽  
Magnetic Resonance Elastography ◽  
Muscle Stiffness ◽  
Muscle Quality ◽  
Tissue Stiffness ◽  
Age Range

A common complication associated with aging is the stiffening of skeletal muscles. The purpose of this study was to determine the ability of magnetic resonance elastography (MRE) to study this phenomenon in vivo. Twenty female subjects were included in the study with an age range of 50 to 70 years. Shear modulus was calculated for the tibialis anterior of each subject. There was not a significant relationship between age and shear modulus. However, three subjects had abnormally high values and were among the oldest subjects tested. There was a significant relationship between age and tissue stiffness homogeneity. More research is needed to determine whether the changes seen here are reflective of increased tissue cross-linking or related to reduced muscle quality. However, MRE shows promise as a tool to study aging-related muscle stiffness changes or to evaluate treatments to counteract these changes.

Initial In-Vivo Results Considering Rayleigh Damping in Magnetic Resonance Elastography

2009 ◽  
Author(s):  
D. Viviers ◽  
E. E. W. Van Houten ◽  
M. D. J. McGarry ◽  
J. B. Weaver ◽  
K. D. Paulsen
Keyword(s):  
Magnetic Resonance ◽  
Soft Tissue ◽  
Shear Modulus ◽  
Material Properties ◽  
Magnetic Resonance Elastography ◽  
Imaginary Component ◽  
Non Invasive ◽  
Rayleigh Damping ◽  
Time Harmonic ◽  
Complex Valued

Dispersive material properties provide valuable metrics for characterizing the nature of soft tissue lesions. Magnetic Resonance Elastography (MRE) targets non-invasive breast cancer diagnosis and is capable of imaging the damping properties of soft tissue. 3D time-harmonic displacement data obtained via MRI is used to drive a reconstruction algorithm capable of deducing the distribution of mechanical properties in the tissue. To make the most of this diagnostic capability, characterization of the damping behavior of tissue is made more sophisticated by the use of a Rayleigh damping model. To date, time-harmonic motion attenuation in tissue as found in dynamic MRE has been characterized by a single parameter model 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. We have implemented a Rayleigh damping reconstruction method for MRE and measured the dispersive properties of actual patient data sets with impressive results. Reconstructions show a close match with varying tissue structure. The reconstructed values for real shear modulus and overall damping levels are in reasonable agreement with values established in the literature or measured by mechanical testing, and in the case of malignant lesions, show good correspondence with contrast enhanced MRI. There is significant medical potential for an algorithm that can accurately reconstruct soft tissue material properties through non invasive MRI scans. Imaging methods that help identify invasive regions through reconstruction of dispersive soft tissue properties could be applied to pathologies in the brain, lung, liver and kidney as well.

scholarly journals Mechanical Properties of Viscoelastic Media by Local Frequency Estimation of Divergence-Free Wave Fields

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Erik H. Clayton ◽  
Ruth J. Okamoto ◽  
Philip V. Bayly
Keyword(s):  
Mechanical Properties ◽  
Magnetic Resonance ◽  
Shear Modulus ◽  
Rigid Body ◽  
Frequency Estimation ◽  
Magnetic Resonance Elastography ◽  
Rigid Body Motion ◽  
Body Motion ◽  
Wave Fields ◽  
Longitudinal Waves

Magnetic resonance elastography (MRE) is an imaging modality with which mechanical properties can be noninvasively measured in living tissue. Magnetic resonance elastography relies on the fact that the elastic shear modulus determines the phase velocity and, hence the wavelength, of shear waves which are visualized by motion-sensitive MR imaging. Local frequency estimation (LFE) has been used to extract the local wavenumber from displacement wave fields recorded by MRE. LFE -based inversion is attractive because it allows material parameters to be estimated without explicitly invoking the equations governing wave propagation, thus obviating the need to numerically compute the Laplacian. Nevertheless, studies using LFE have not explicitly addressed three important issues: (1) tissue viscoelasticity; (2) the effects of longitudinal waves and rigid body motion on estimates of shear modulus; and (3) mechanical anisotropy. In the current study we extend the LFE technique to (1) estimate the (complex) viscoelastic shear modulus in lossy media; (2) eliminate the effects of longitudinal waves and rigid body motion; and (3) determine two distinct shear moduli in anisotropic media. The extended LFE approach is demonstrated by analyzing experimental data from a previously-characterized, isotropic, viscoelastic, gelatin phantom and simulated data from a computer model of anisotropic (transversely isotropic) soft material.

Magnetic Resonance Elastography of the Mouse Brain In Vivo

2007 ◽  
Author(s):  
Stefan M. Atay ◽  
Philip V. Bayly
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Mouse Brain ◽  
Ex Vivo ◽  
Magnetic Resonance Elastography ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
High Deformation ◽  
Nonlinear Viscoelastic

In the current study we apply the magnetic resonance elastography (MRE) technique to estimate the dynamic shear modulus of mouse brain tissue in vivo. The frequency used (1200 Hz) is well above those reported previously [1]. Estimates of dynamic shear modulus range from 12,600–14,800 N/m2 at 1200 Hz. These data are strictly relevant only to small oscillations at this specific frequency, but these values are obtained at high frequencies (and thus high deformation rates) and non-invasively throughout the brain. These data complement measurements of nonlinear viscoelastic properties obtained by others at slower rates, either ex vivo or invasively.

scholarly journals Changes in calf muscle elasticity in hypogonadal males before and after testosterone substitution as monitored by magnetic resonance elastography

2007 ◽  
Vol 156 (6) ◽  
pp. 673-678 ◽  
Author(s):  
Katja Brauck ◽  
Craig J Galbán ◽  
Stefan Maderwald ◽  
Burkhard L Herrmann ◽  
Mark E Ladd
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Maximum Voluntary Contraction ◽  
Magnetic Resonance Elastography ◽  
Control Group ◽  
Therapeutic Effects ◽  
Muscle Elasticity ◽  
Testosterone Levels ◽  
Age Related ◽  
Testosterone Substitution

Purpose: We sought to determine whether differences in muscle elasticity between healthy age-related controls and patients with hypogonadism could be measured by a new, non-invasive method termed magnetic resonance elastography (MRE). Materials and methods: Twelve hypogonadal (21–68 years) and twenty-seven healthy age-related men (20–76 years) were examined. In the hypogonadism group, serum testosterone levels were compared and MRE was conducted prior to and after 6 months of therapy in 6 of the 12 patients. MRE was performed by mechanically exciting the soleus muscle that was used because of its uniformly distributed muscle fibers, size, and accessibility, with a custom designed piezoelectric-actuator using a modified phase-contrast sequence. For mechanical excitation the actuator lever was placed on the anterior surface of the calf. The subjects had to maintain a force of 0–20% of their maximum voluntary contraction against a home-built footplate that was mounted on the MR table. All images were phase unwrapped and reconstructed into shear modulus elastograms using the local frequency estimation technique. Results: Testosterone levels were significantly higher after 6 months of treatment. A statistical difference in the shear modulus was observed prior to and after 6 months of testosterone therapy and was nearly the same as in the healthy age-related control group. Conclusion: MRE seems to be a promising technique for the evaluation of therapeutic effects in patients with hypogonadism and possibly in other diseases with muscular effects.

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