Magnetic Resonance Elastography of Rodent Brain

Abstract

Magnetic resonance elastography (MRE) is a non-invasive imaging technique, using the propagation of mechanical waves as a probe to palpate biological tissues. It consists in three main steps: production of shear waves within the tissue; encoding subsequent tissue displacement in magnetic resonance images; and extraction of mechanical parameters based on dedicated reconstruction methods. These three steps require an acoustic-frequency mechanical actuator, magnetic resonance imaging acquisition, and a post-processing tool for which no turnkey technology is available. The aim of the present review is to outline the state of the art of reported set-ups to investigate rodent brain mechanical properties. The impact of experimental conditions in dimensioning the set-up (wavelength and amplitude of the propagated wave, spatial resolution, and signal-to-noise ratio of the acquisition) on the accuracy and precision of the extracted parameters is discussed, as well as the influence of different imaging sequences, scanners, electromagnetic coils, and reconstruction algorithms. Finally, the performance of MRE in demonstrating viscoelastic differences between structures constituting the physiological rodent brain, and the changes in brain parameters under pathological conditions, are summarized. The recently established link between biomechanical properties of the brain as obtained on MRE and structural factors assessed by histology is also studied. This review intends to give an accessible outline on how to conduct an elastography experiment, and on the potential of the technique in providing valuable information for neuroscientists.

Longitudinal shear waves for elastic characterization of tissues in optical coherence elastography

“…An experiment involving mouse brain elastography using LSW was performed and demonstrated that the cerebellum and midbrain were found to be softer than the cerebral cortex. This is consistent with various magnetic resonance elastography studies which have shown similar findings in both mice and humans [25,[33][34][35]. In these studies, a general trend for shear storage modulus is from 4 kPa to 16 kPa for the cerebral cortex, and from 1 kPa to 4 kPa for the cerebellum/midbrain.…”

“…The gel in between the coverslip and brain tissue (thickness ∼0.1 mm) serves as an elastic coupling medium. The shear wave speed in the 2% concentration agarose gel was measured to be 2.67 ± 0.05 m/s, which is in the range of previously reported shear wave speed in mouse brain [25] and avoids the creation of strong wave reflections.…”

MR Elastography-Based Assessment of Matrix Remodeling at Lesion Sites Associated With Clinical Severity in a Model of Multiple Sclerosis

“…Magnetic resonance elastography (MRE) could represent a promising alternative to the use of GBCA. MRE provides information about the mechanical properties of tissues (7,8) by analyzing their response to oscillatory shear stress (9). Using MRE, we reported on reduced brain viscoelasticity in patients with clinically isolated syndrome (10) as well as patients with established relapsing-remitting (11) and chronic-progressive (12) MS.…”

Role of gadolinium-based contrast agents in neurological disorders

“…The research of Bigot et al performed on a relapsing-remitting EAE model shows that a reduction of brain stiffness correlates with clinical disability and is associated with enhanced expression of the extracellular matrix protein fibronectin. These results taken together suggest that MRE could potentially emerge as a safe tool to monitor MS activity [83].…”