Separation of fluid and solid shear wave fields and quantification of coupling density by magnetic resonance poroelastography

Lilaj, Ledia; Fischer, Thomas; Guo, Jing; Braun, Jürgen; Sack, Ingolf; Hirsch, Sebastian

doi:10.1002/mrm.28507

Cited by 15 publications

(19 citation statements)

References 32 publications

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“…This consistency of multifrequency data further validates the technique of rt-MMRE. Furthermore, this observation indicates that the poroelastic response of brain tissue ( Lilaj et al, 2020 ) is similar at 30 and 40 Hz ( McGarry et al, 2015 ). Additional validation of rt-MMRE was obtained by reference experiments performed during breath-holds but without sustained VM.…”

Section: Discussionmentioning

confidence: 71%

“…In complex multiphasic mechanical systems such as the brain, shear modulus and pressure are linked through poroelastic interactions between the fluid and solid spaces ( Bilston, 2002 ; Tully and Ventikos, 2011 ; Parker, 2014 ). Thus, it is likely that regulation of ICP, which is one of the most important vital functions of intracranial mechanics, also affects shear viscoelasticity ( Perrinez et al, 2009 ; McGarry et al, 2015 ; Lilaj et al, 2020 ). However, this mechanical component of cerebral autoregulation is largely unstudied due to a lack of imaging techniques that can measure cerebral shear modulus in vivo with high spatial and temporal resolution.…”

Section: Introductionmentioning

confidence: 99%

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Real-Time Multifrequency MR Elastography of the Human Brain Reveals Rapid Changes in Viscoelasticity in Response to the Valsalva Maneuver

Herthum

Shahryari

Tzschätzsch

et al. 2021

Front. Bioeng. Biotechnol.

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Modulation of cerebral blood flow and vascular compliance plays an important role in the regulation of intracranial pressure (ICP) and also influences the viscoelastic properties of brain tissue. Therefore, magnetic resonance elastography (MRE), the gold standard for measuring in vivo viscoelasticity of brain tissue, is potentially sensitive to cerebral autoregulation. In this study, we developed a multifrequency MMRE technique that provides serial maps of viscoelasticity at a frame rate of nearly 6 Hz without gating, i.e., in quasi-real time (rt-MMRE). This novel method was used to monitor rapid changes in the viscoelastic properties of the brains of 17 volunteers performing the Valsalva maneuver (VM). rt-MMRE continuously sampled externally induced vibrations comprising three frequencies of 30.03, 30.91, and 31.8 Hz were over 90 s using a steady-state, spiral-readout gradient-echo sequence. Data were processed by multifrequency dual elasto-visco (MDEV) inversion to generate maps of magnitude shear modulus | G∗| (stiffness) and loss angle φ at a frame rate of 5.4 Hz. As controls, the volunteers were examined to study the effects of breath-hold following deep inspiration and breath-hold following expiration. We observed that | G∗| increased while φ decreased due to VM and, less markedly, due to breath-hold in inspiration. Group mean VM values showed an early overshoot of | G∗| 2.4 ± 1.2 s after the onset of the maneuver with peak values of 6.7 ± 4.1% above baseline, followed by a continuous increase in stiffness during VM. A second overshoot of | G∗| occurred 5.5 ± 2.0 s after the end of VM with peak values of 7.4 ± 2.8% above baseline, followed by 25-s sustained recovery until the end of image acquisition. φ was constantly reduced by approximately 2% during the entire VM without noticeable peak values. This is the first report of viscoelasticity changes in brain tissue induced by physiological maneuvers known to alter ICP and detected by clinically applicable rt-MMRE. Our results show that apnea and VM slightly alter brain properties toward a more rigid-solid behavior. Overshooting stiffening reactions seconds after onset and end of VM reveal rapid autoregulatory processes of brain tissue viscoelasticity.

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Section: Discussionmentioning

confidence: 71%

Section: Introductionmentioning

confidence: 99%

Real-Time Multifrequency MR Elastography of the Human Brain Reveals Rapid Changes in Viscoelasticity in Response to the Valsalva Maneuver

Herthum

Shahryari

Tzschätzsch

et al. 2021

Front. Bioeng. Biotechnol.

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“…The MRE data were acquired with a single‐shot, spin‐echo EPI sequence as described previously 15 . For IR‐MRE, the 90° pulse was preceded by a slice‐selective inversion pulse with an inversion time (TI) of 1970 ms in the phantom study and 2800 ms in the in vivo experiments.…”

Section: Methodsmentioning

confidence: 99%

Inversion‐recovery MR elastography of the human brain for improved stiffness quantification near fluid–solid boundaries

Lilaj

Herthum

Meyer

et al. 2021

Magnetic Resonance in Med

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Purpose In vivo MR elastography (MRE) holds promise as a neuroimaging marker. In cerebral MRE, shear waves are introduced into the brain, which also stimulate vibrations in adjacent CSF, resulting in blurring and biased stiffness values near brain surfaces. We here propose inversion‐recovery MRE (IR‐MRE) to suppress CSF signal and improve stiffness quantification in brain surface areas. Methods Inversion‐recovery MRE was demonstrated in agar‐based phantoms with solid‐fluid interfaces and 11 healthy volunteers using 31.25‐Hz harmonic vibrations. It was performed by standard single‐shot, spin‐echo EPI MRE following 2800‐ms IR preparation. Wave fields were acquired in 10 axial slices and analyzed for shear wave speed (SWS) as a surrogate marker of tissue stiffness by wavenumber‐based multicomponent inversion. Results Phantom SWS values near fluid interfaces were 7.5 ± 3.0% higher in IR‐MRE than MRE (P = .01). In the brain, IR‐MRE SNR was 17% lower than in MRE, without influencing parenchymal SWS (MRE: 1.38 ± 0.02 m/s; IR‐MRE: 1.39 ± 0.03 m/s; P = .18). The IR‐MRE tissue–CSF interfaces appeared sharper, showing 10% higher SWS near brain surfaces (MRE: 1.01 ± 0.03 m/s; IR‐MRE: 1.11 ± 0.01 m/s; P < .001) and 39% smaller ventricle sizes than MRE (P < .001). Conclusions Our results show that brain MRE is affected by fluid oscillations that can be suppressed by IR‐MRE, which improves the depiction of anatomy in stiffness maps and the quantification of stiffness values in brain surface areas. Moreover, we measured similar stiffness values in brain parenchyma with and without fluid suppression, which indicates that shear wavelengths in solid and fluid compartments are identical, consistent with the theory of biphasic poroelastic media.

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“…Another approach to highlight brain poroelasticity was to solve for both shear and bulk moduli using the algebraic inversion technique, which resulted in a bulk modulus much lower than expected, confirming the poroelastic nature of the brain (compressible solid matrix and incompressible fluid channels) [209]. More recently was proposed an improvement in MR poroelastography acquisition processes allowing to separate solid and fluid contributions to the shear motion field using an inversion recovery sequence adapted to MRE, along with a tailored MR signal modeling [295].…”

Section: Brain Anisotropy and Poroelasticitymentioning

confidence: 97%

Viscoelasticity Imaging of Biological Tissues and Single Cells Using Shear Wave Propagation

Flé

Bhatt

et al. 2021

Front. Phys.

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Changes in biomechanical properties of biological soft tissues are often associated with physiological dysfunctions. Since biological soft tissues are hydrated, viscoelasticity is likely suitable to represent its solid-like behavior using elasticity and fluid-like behavior using viscosity. Shear wave elastography is a non-invasive imaging technology invented for clinical applications that has shown promise to characterize various tissue viscoelasticity. It is based on measuring and analyzing velocities and attenuations of propagated shear waves. In this review, principles and technical developments of shear wave elastography for viscoelasticity characterization from organ to cellular levels are presented, and different imaging modalities used to track shear wave propagation are described. At a macroscopic scale, techniques for inducing shear waves using an external mechanical vibration, an acoustic radiation pressure or a Lorentz force are reviewed along with imaging approaches proposed to track shear wave propagation, namely ultrasound, magnetic resonance, optical, and photoacoustic means. Then, approaches for theoretical modeling and tracking of shear waves are detailed. Following it, some examples of applications to characterize the viscoelasticity of various organs are given. At a microscopic scale, a novel cellular shear wave elastography method using an external vibration and optical microscopy is illustrated. Finally, current limitations and future directions in shear wave elastography are presented.

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Separation of fluid and solid shear wave fields and quantification of coupling density by magnetic resonance poroelastography

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 15 publications

References 32 publications

Real-Time Multifrequency MR Elastography of the Human Brain Reveals Rapid Changes in Viscoelasticity in Response to the Valsalva Maneuver

Real-Time Multifrequency MR Elastography of the Human Brain Reveals Rapid Changes in Viscoelasticity in Response to the Valsalva Maneuver

Inversion‐recovery MR elastography of the human brain for improved stiffness quantification near fluid–solid boundaries

Viscoelasticity Imaging of Biological Tissues and Single Cells Using Shear Wave Propagation

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