MR elastography: Principles, guidelines, and terminology

Abstract

MANDUCA et Al. per year is increasing rapidly (Figure 1). However, numerous types of acquisitions and processing techniques are in use, and MRE results have been expressed in many different quantities: shear modulus (possibly complex), storage modulus, magnitude of the complex shear modulus, shear stiffness (defined in different ways), wave speed, propagation, loss modulus, attenuation, loss tangent or loss factor, phase angle, damping ratio, attenuation, and penetration rate. This list is not exhaustive and does not include additional quantities related to fitting specific assumed material models or anisotropic materials. This diversity of terminology and absence of standardization can lead to confusion (particularly among clinicians) as to the meaning of certain terms, or how to interpret or compare certain types of MRE results. This paper is written by the MRE Guidelines Committee, a group formalized at the first meeting of the ISMRM MRE Study Group, to attempt to clarify and (to some extent) standardize MRE terminology and practice. Specifically, the purpose of this paper is to (1) explain MRE terminology to those not familiar with it, (2) define "good practices" for practitioners of MRE, and (3) discuss some practices and terms that we believe should be standardized and some that should be discouraged. F I G U R E 2 Schematic stress-strain relationship for soft tissue unloaded and at three different tissue-loading states. Magnetic resonance elastography measures the slope of this curve at a given point, as indicated by the tangent line at ε 3

Contribution of Tissue Inflammation and Blood-Brain Barrier Disruption to Brain Softening in a Mouse Model of Multiple Sclerosis

“…It is already well documented that neuroinflammation modifies the viscoelastic properties of neuronal tissue, reducing stiffness throughout larger brain areas ( Wuerfel et al, 2010 ; Streitberger et al, 2012 ) ( Riek et al, 2012 ; Millward et al, 2015 ; Fehlner et al, 2016 ; Wang et al, 2020 ). MRE uses harmonic vibrations to transmit shear waves into the tissue of interest ( Manduca et al, 2021 ). Wave propagation is detected using motion-sensitive MRI, from which viscoelastic parameters such as stiffness (magnitude shear modulus or shear wave speed) and fluidity (viscosity, dispersion angle or loss angle of the shear modulus) are derived ( Hirsch et al, 2017 ).…”

Targeted Blood Brain Barrier Opening With Focused Ultrasound Induces Focal Macrophage/Microglial Activation in Experimental Autoimmune Encephalomyelitis

“…This is quantifiable using magnetic resonance elastography (MRE) and changes of cerebral biomechanics have been demonstrated in animal models ( Riek et al, 2012 ; Schregel et al, 2012 ; Millward et al, 2015 ; Wang et al, 2020 ) and in patients with MS ( Wuerfel et al, 2010 ; Streitberger et al, 2012 ; Fehlner et al, 2015 ). Briefly, MRE is a phase contrast-based magnetic resonance imaging (MRI) technique that measures tissue displacement caused by propagating mechanical shear waves ( Muthupillai and Ehman, 1996 ; Manduca et al, 2020 ). Biomechanical properties can be inferred from the displacement field ( Fovargue et al, 2018 ) and allow for the quantification of tissue stiffness, for example.…”

MRI Measures of Murine Liver Fibrosis

“…There is a need for a noninvasive method, such as magnetic resonance imaging (MRI), that can be used to detect and quantify liver fibrosis in CLD. MRI techniques that have been applied to CLD include proton density fat fraction (PDFF), 7 T 1 and T 2 relaxation time mapping, 8 T 1rho relaxation, 9 and MR elastography (MRE) 10 . Application of these techniques can be confounded by fibrosis, inflammation, and other factors (eg, hepatic congestion, steatosis 11 ); none have completely replaced liver biopsy.…”