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

Area of Science:

• Neuroimaging
• Biophysics
• Medical Physics

Background:

• Accurate mapping of brain tissue stiffness is crucial for understanding neurological function and disease.
• Previous magnetic resonance elastography (MRE) methods faced limitations in speed and resolution for in vivo mouse brain applications.

Purpose of the Study:

• To develop and validate in vivo multifrequency single-shot MRE for comprehensive stiffness mapping of the entire mouse brain.
• To compare the stiffness of neural tissues with varying white-to-gray matter ratios.
• To evaluate the performance of tomoelastography against algebraic Helmholtz inversion (AHI) for shear wave speed (SWS) analysis.

Main Methods:

• Utilized 7T small-animal MRI with a single-shot spin-echo planar imaging MRE sequence.
• Acquired wave images across six mechanical vibration frequencies (900-1400 Hz) in viscous phantoms and 10 C57BL-6 mice.
• Computed SWS maps using tomoelastography and compared with AHI, analyzing signal-to-noise ratio (SNR) across brain regions.

Main Results:

• Tomoelastography provided consistent SWS measurements across the full SNR range, unlike AHI which was biased by noise.
• Mean in vivo SWS of the mouse brain was 3.76 ± 0.33 m/s.
• Significant regional variations in SWS were observed, with the hippocampus (4.91 ± 0.49 m/s) and diencephalon (4.78 ± 0.78 m/s) being stiffer than the cerebral cortex (3.53 ± 0.29 m/s) and corpus callosum (2.89 ± 0.17 m/s).

Conclusions:

• Tomoelastography enables faster and higher-resolution mouse brain stiffness mapping compared to traditional AHI-based MRE.
• The study demonstrates that mouse white matter is measurably softer than gray matter at the investigated frequencies.
• This technique provides valuable insights into the mechanical properties of brain tissues.