Concurrent <scp>3D</scp> acquisition of diffusion tensor imaging and magnetic resonance elastography displacement data (<scp>DTI‐MRE</scp>): Theory and in vivo application

Yin, Ziying; Kearney, Steven; Magin, Richard L.; Klatt, Dieter

doi:10.1002/mrm.26121

Cited by 23 publications

(29 citation statements)

References 48 publications

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“…10,11,14,24 The recent development of a 3D multislab, multishot acquisition for whole-brain MRE could achieve high signal-to-noise efficacy. [25][26][27][28][29] 3D analysis could improve the results if the wave propagation is complicated, especially if there is throughplane oblique wave propagation that a 2D analysis would not visualize correctly.…”

Section: Discussionmentioning

confidence: 99%

Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

Sakai¹,

Takehara²,

Yamashita

et al. 2016

AJNR Am J Neuroradiol

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Section: Discussionmentioning

confidence: 99%

Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

Sakai¹,

Takehara²,

Yamashita

et al. 2016

AJNR Am J Neuroradiol

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“…However, the displacement is a continuous function in space and hence application of a MEG leads to IVPD. This, in turn, can be shown to lead to magnitude fluctuations, which depend on the voxel size, the shear wavelength and the sensitizing gradient . The ratio of the magnitude image with and without IVPD can be calculated by solving the integral

R_{i, k} ((), {\vec{x}}_{c}) = (||, \frac{1}{V} \int_{{normalΩ}_{V}} d^{3} x e^{normali φ_{i, k} ((), \vec{x} + {\overset{true\to}{x}}_{c})}) .

…”

Section: Theorymentioning

confidence: 99%

Analysis and improvement of motion encoding in magnetic resonance elastography

et al. 2018

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Magnetic resonance elastography (MRE) utilizes phase contrast magnetic resonance imaging (MRI), which is phase locked to externally generated mechanical vibrations, to measure the three-dimensional wave displacement field. At least four measurements with linear-independent encoding directions are necessary to correct for spurious phase contributions if effects from imaging gradients are non-negligible. In MRE, three encoding schemes have been used: unbalanced four- and six-point and balanced four-point ('tetrahedral') encoding. The first two sensitize to motion with orthogonal gradients, with the four-point method acquiring a single reference scan without motion sensitization, whereas three additional scans with inverted gradients are used with six-point encoding, leading to two-fold higher displacement-to-noise ratio (DNR) and 50% longer scan duration. Balanced four-point (tetrahedral) encoding encodes along the four diagonals of a cube, with one direction serving as a reference for the other three encoding directions, similar to four-point encoding. The objective of this work is to introduce a theoretical framework to compare different motion sensitization strategies with respect to their motion encoding efficiency in two fundamental encoding limits, the gradient strength limit and the dynamic range limit, which are both placed in relation to conventional gradient recalled echo (GRE)- and spin echo (SE)-based MRE sequences. We apply the framework to the three aforementioned schemes and show that the motion encoding efficiency of unbalanced four- and six-point encoding schemes in the gradient-limited regime can be increased by a factor of 1.5 when using all physical gradient channels concurrently. Furthermore, it is demonstrated that reversing the direction of the reference in balanced four-point (tetrahedral) encoding results in the Hadamard encoding scheme, which leads to increased DNR by 2 compared with balanced four-point encoding and 2.8 compared with unbalanced four-point encoding. As an example, we show that optimal encoding can be utilized to reduce the acquisition time of standard liver MRE in vivo from four to two breath holds.

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“…However, in these studies, separate scans for DTI and MRE datasets were performed. Since MRE uses the phase‐contrast principle with strong gradients for the displacement detection, diffusion weighting can be simultaneously encoded in the magnitude of the complex signal (diffusion MRE, dMRE), leading to co‐registered datasets . The acquisition of diffusion‐weighted images together with MRE is straightforward, since only the b ‐value of the applied MEGs needs to be calculated and if needed optimized to achieve a certain diffusion weighting without destroying the phase‐locked nature of the MEGs in MRE .…”

Section: Unconventional Mre Acquisition Techniquesmentioning

confidence: 99%

“…C, Real component of complex wave image and corresponding elastogram acquired from dMRE (top) and conventional MRE (bottom). (Figure and text taken from Reference )…”

Section: Unconventional Mre Acquisition Techniquesmentioning

confidence: 99%

“…All diffusion directions are then acquired using the same gradient waveform, but with varying mechanical phase offsets. In this way, a full three‐directional MRE dataset as well as the full diffusion tensor can be encoded . Drawbacks of the dMRE and DTI‐MRE are local noise enhancement due to strong diffusion weighting ( PNR ∝ SNR ∝ e − bD ) as well as intra‐voxel phase dispersion.…”

Section: Unconventional Mre Acquisition Techniquesmentioning

confidence: 99%

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Encoding and readout strategies in magnetic resonance elastography

Guenthner

Kozerke

2018

NMR in Biomedicine

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Magnetic resonance elastography (MRE) has evolved significantly since its inception. Advances in motion-encoding gradient design and readout strategies have led to improved encoding and signal-to-noise ratio (SNR) efficiencies, which in turn allow for higher spatial resolution, increased coverage, and/or shorter scan times. The purpose of this review is to summarize MRE wave-encoding and readout approaches in a unified mathematical framework to allow for a comparative assessment of encoding and SNR efficiency of the various methods available. Besides standard full- and fractional-wave-encoding approaches, advanced techniques including flow compensation, sample interval modulation and multi-shot encoding are considered. Signal readout using fast k-space trajectories, reduced field of view, multi-slice, and undersampling techniques are summarized and put into perspective. The review is concluded with a foray into displacement and diffusion encoding as alternative and/or complementary techniques.

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Concurrent 3D acquisition of diffusion tensor imaging and magnetic resonance elastography displacement data (DTI‐MRE): Theory and in vivo application

Cited by 23 publications

References 48 publications

Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

Shear Stiffness of 4 Common Intracranial Tumors Measured Using MR Elastography: Comparison with Intraoperative Consistency Grading

Analysis and improvement of motion encoding in magnetic resonance elastography

Encoding and readout strategies in magnetic resonance elastography

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