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 Measurement of the Dynamic Shear Modulus of Mouse Brain Tissue In Vivo by Magnetic Resonance Elastography

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
Stefan M. Atay ◽  
Christopher D. Kroenke ◽  
Arash Sabet ◽  
Philip V. Bayly
Keyword(s):  
Magnetic Resonance ◽  
Shear Modulus ◽  
Brain Tissue ◽  
Mouse Brain ◽  
Ex Vivo ◽  
Three Dimensions ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
High Deformation

In this study, the magnetic resonance (MR) elastography technique was used to estimate the dynamic shear modulus of mouse brain tissue in vivo. The technique allows visualization and measurement of mechanical shear waves excited by lateral vibration of the skull. Quantitative measurements of displacement in three dimensions during vibration at 1200Hz were obtained by applying oscillatory magnetic field gradients at the same frequency during a MR imaging sequence. Contrast in the resulting phase images of the mouse brain is proportional to displacement. To obtain estimates of shear modulus, measured displacement fields were fitted to the shear wave equation. Validation of the procedure was performed on gel characterized by independent rheometry tests and on data from finite element simulations. Brain tissue is, in reality, viscoelastic and nonlinear. The current estimates of dynamic shear modulus are strictly relevant only to small oscillations at a specific frequency, but these estimates may be obtained at high frequencies (and thus high deformation rates), noninvasively throughout the brain. These data complement measurements of nonlinear viscoelastic properties obtained by others at slower rates, either ex vivo or invasively.

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 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.

scholarly journals Automated Segmentation of in Vivo and Ex Vivo Mouse Brain Magnetic Resonance Images

2009 ◽  
Vol 8 (1) ◽  
pp. 7290.2009.00004 ◽  
Author(s):  
Alize E.H. Scheenstra ◽  
Rob C.G. van de Ven ◽  
Louise van der Weerd ◽  
Arn M.J.M. van den Maagdenberg ◽  
Jouke Dijkstra ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Mouse Brain ◽  
Ex Vivo ◽  
Magnetic Resonance Images ◽  
Automated Segmentation

Shear Modulus and Damping Ratio of Gravel Material

2011 ◽  
Vol 105-107 ◽  
pp. 1426-1432 ◽  
Author(s):  
De Gao Zou ◽  
Tao Gong ◽  
Jing Mao Liu ◽  
Xian Jing Kong
Keyword(s):  
Shear Modulus ◽  
Shear Strain ◽  
Strain Amplitude ◽  
Damping Ratio ◽  
Confining Pressure ◽  
Dynamic Shear Modulus ◽  
Test Results ◽  
Dynamic Shear ◽  
Data Points ◽  
Shear Strain Amplitude

Two of the most important parameters in dynamic analysis involving soils are the dynamic shear modulus and the damping ratio. In this study, a series of tests were performed on gravels. For comparison, some other tests carried out by other researchers were also collected. The test results show that normalized shear modulus and damping ratio vary with the shear strain amplitude, (1) normalized shear modulus decreases with the increase of dynamic shear strain amplitude, and as the confining pressure increases, the test data points move from the low end toward the high end; (2) damping ratio increases with the increase of shear strain amplitude, damping ratio is dependent on confining pressure where an increase in confining pressure decreased damping ratio. According to the test results, a reference formula is proposed to evaluate the maximum dynamic shear modulus, the best-fit curve and standard deviation bounds for the range of data points are also proposed.

scholarly journals The effect of fluid saturation on the dynamic shear modulus of tight sandstones

2017 ◽  
Vol 14 (5) ◽  
pp. 1072-1086 ◽  
Author(s):  
Dongqing Li ◽  
Jianxin Wei ◽  
Bangrang Di ◽  
Pinbo Ding ◽  
Da Shuai
Keyword(s):  
Shear Modulus ◽  
Dynamic Shear Modulus ◽  
Dynamic Shear ◽  
Fluid Saturation
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