MR elastography: Principles, guidelines, and terminology

Abstract

Magnetic resonance elastography (MRE) is a phase contrast-based MRI technique that can measure displacement due to propagating mechanical waves, from which material properties such as shear modulus can be calculated. Magnetic resonance elastography can be thought of as quantitative, noninvasive palpation. It is increasing in clinical importance, has become widespread in the diagnosis and staging of liver fibrosis, and additional clinical applications are being explored. However, publications have reported MRE results using many different parameters, acquisition techniques, processing methods, and varied nomenclature. The diversity of terminology can lead to confusion (particularly among clinicians) about the meaning of and interpretation of MRE results. This paper was written by the MRE Guidelines Committee, a group formalized at the first meeting of the ISMRM MRE Study Group, to clarify and move toward standardization of MRE nomenclature. The purpose of this paper is to (1) explain MRE terminology and concepts to those not familiar with them, (2) define "good practices" for practitioners of MRE, and (3) identify opportunities to standardize terminology, to avoid confusion.

Keywords: MR elastography; elasticity imaging; elastography; mechanical properties; tissue stiffness.

FIGURE 1

Number of publications per year returned by Web of Science searches on “elastography” (left, 13 973 total) and “magnetic resonance elastography” or “MR elastography” (right, 2157 total)

FIGURE 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 ε₃