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Magn Reson Med. 2018 Nov 4. doi: 10.1002/mrm.27586. [Epub ahead of print]

Fast tomoelastography of the mouse brain by multifrequency single-shot MR elastography.

Author information

1
Department of Radiology, Charité-Universitätsmedizin Berlin, Campus Charité Mitte, Berlin, Germany.
2
Department of Neurology, Charité-Universitätsmedizin Berlin, Campus Charité Mitte, Berlin, Germany.
3
Institute of Medical Informatics, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Berlin, Germany.

Abstract

PURPOSE:

To introduce in vivo multifrequency single-shot magnetic resonance elastography for full-FOV stiffness mapping of the mouse brain and to compare in vivo stiffness of neural tissues with different white-to-gray matter ratios.

METHODS:

Viscous phantoms and 10 C57BL-6 mice were investigated by 7T small-animal MRI using a single-shot spin-echo planar imaging magnetic resonance elastography sequence with motion-encoding gradients positioned before the refocusing pulse. Wave images were acquired over 10 minutes for 6 mechanical vibration frequencies between 900 and 1400 Hz. Stiffness maps of shear wave speed (SWS) were computed using tomoelastography data processing and compared with algebraic Helmholtz inversion (AHI) for signal-to-noise ratio (SNR) analysis. Different brain regions were analyzed including cerebral cortex, corpus callosum, hippocampus, and diencephalon.

RESULTS:

In phantoms, algebraic Helmholtz inversion-based SWS was systematically biased by noise and discretization, whereas tomoelastography-derived SWS was consistent over the full SNR range analyzed. Mean in vivo SWS of the whole brain was 3.76 ± 0.33 m/s with significant regional variation (hippocampus = 4.91 ± 0.49 m/s, diencephalon = 4.78 ± 0.78 m/s, cerebral cortex = 3.53 ± 0.29 m/s, and corpus callosum = 2.89 ± 0.17 m/s).

CONCLUSION:

Tomoelastography retrieves mouse brain stiffness within shorter scan times and with greater detail resolution than classical algebraic Helmholtz inversion-based magnetic resonance elastography. The range of SWS values obtained here indicates that mouse white matter is softer than gray matter at the frequencies investigated.

KEYWORDS:

elasticity; mouse brain; multifrequency magnetic resonance elastography; shear wave speed

PMID:
30393887
DOI:
10.1002/mrm.27586

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