REVIEW
Magnetic Resonance Elastography: A Review
YOGESH K. MARIAPPAN,
*
KEVIN J. GLASER, AND RICHARD L. EHMAN
1
*
Department of Radiology, Mayo Clinic, Rochester, Minnesota
Magnetic resonance elastography (MRE) is a rapidly developing technology for
quantitatively assessing the mechanical properties of tissue. The technology
can be considered to be an imaging-based counterpart to palpation, commonly
used by physicians to diagnose and characterize diseases. The success of pal-
pation as a diagnostic method is based on the fact that the mechanical proper-
ties of tissues are often dramatically affected by the presence of disease proc-
esses, such as cancer, inflammation, and fibrosis. MRE obtains information
about the stiffness of tissue by assessing the propagation of mechanical waves
through the tissue with a special magnetic resonance imaging technique. The
technique essentially involves three steps: (1) generating shear waves in the
tissue, (2) acquiring MR images depicting the propagation of the induced shear
waves, and (3) processing the images of the shear waves to generate quanti-
tative maps of tissue stiffness, called elastograms. MRE is already being used
clinically for the assessment of patients with chronic liver diseases and is
emerging as a safe, reliable, and noninvasive alternative to liver biopsy for
staging hepatic fibrosis. MRE is also being investigated for application to
pathologies of other organs including the brain, breast, blood vessels, heart,
kidneys, lungs, and skeletal muscle. The purpose of this review article is to
introduce this technology to clinical anatomists and to summarize some of the
current clinical applications that are being pursued. Clin. Anat. 23:497–511,
2010. V
C
2010 Wiley-Liss, Inc.
Key words: elasticity imaging; palpation; mechanical properties; shear stiff-
ness
INTRODUCTION
The use of palpation to feel the difference in the
mechanical properties of tissues and to differentiate
abnormal and normal tissues remains a time-tested
diagnostic tool for physicians. The mechanical prop-
erties of tissues vary widely among different physio-
logical and pathological states (Duck, 1990; Sar-
vazyan et al., 1995) and hence have significant diag-
nostic potential. For instance, the relative hardness
of malignant tumors is the basis for the use of palpa-
tion to detect breast cancer (Barton et al., 1999).
Surgeons often detect liver tumors by simple touch
at laparotomy that may not have been detected in
preoperative imaging (Elias et al., 2005). However,
except at surgery, palpation is applicable only to su-
perficial organs and pathologies and is qualitative,
subjective and limited to the touch sensitivity of the
practitioner. Unfortunately, none of the conventional
medical imaging techniques, such as computed to-
mography (CT), magnetic resonance imaging (MRI),
and ultrasonography (US), are capable of depicting
the properties that are assessed by palpation. These
considerations have provided motivation for develop-
ing special imaging technologies for quantitatively
assessing the mechanical properties of tissue.
*Correspondence to: Yogesh K. Mariappan, Department of Radiol-
ogy, Mayo Clinic, 200 First Street SW, Rochester, MN 55905.
E-mail: mariappan.yogesh@mayo.edu (or) Richard L. Ehman,
Department of Radiology, Mayo Clinic, 200 First Street SW, Roch-
ester, MN 55905. E-mail: Ehman.Richard@mayo.edu
Grant sponsor: NIH; Grant number: EB001981
Received 29 December 2009; Revised 13 April 2010; Accepted
20 April 2010
Published online 7 June 2010 in Wiley InterScience (www.
interscience.wiley.com). DOI 10.1002/ca.21006
VC 2010 Wiley-Liss, Inc.
Clinical Anatomy 23:497–511 (2010)

In engineering terms, the property assessed by
palpation is called the elastic modulus. As shown in
Figure 1, the elastic modulus of tissues varies by
over five orders of magnitude and the tissue proper-
ties assessed by other modalities, such as US, CT,
and MRI vary over a much smaller scale.
ELASTICITY IMAGING
Investigators have evaluated a number of differ-
ent approaches for imaging the mechanical proper-
ties of tissue. Most of the elasticity imaging methods
apply some kind of stress or mechanical excitation to
the tissue, measure the tissue response to this stim-
ulus, and from this response calculate parameters
that reflect the mechanical properties. Figure 2
shows a classification of these various approaches
based on the three essential steps in elasticity imag-
ing.
A detailed review of all of the approaches is
beyond the scope of this article; however some of
the primary methods are highlighted below so that
the reader can appreciate the breadth of the field.
More technical discussions can be found in the litera-
ture, such as in (Sarvazyan et al., 1995; Wilson
et al., 2000; Greenleaf et al., 2003).
Excitation Application
The mechanical stress that is applied to tissue
can be produced either through internal sources of
motion, such as respiration or cardiac pulsations
(Mai and Insana, 2002; Kanai, 2004; Bae et al.,
2007) or through external mechanical sources of
motion (Bercoff et al., 2004; Xu et al., 2007; Kruse
et al., 2008). The stimulus can also be classified
based on the temporal characteristics of the excita-
tion as static (or quasistatic) or dynamic. Manual
palpation can be thought of as a static elasticity
assessment technique. Static compressions are
Fig. 1. Imaging modality contrast mechanisms.
Examples of different imaging modalities and the spec-
trum of contrast mechanisms utilized by them are
shown. The shear modulus has the largest variation
with variations over five orders of magnitude among
various physiological states of normal and pathologic
tissues.
Fig. 2. Various approaches to elasticity imaging.
The flowchart lists the various approaches to the three
basic steps to elasticity imaging: (1) excitation applica-
tion, (2) tissue response detection, and (3) calculation
of the mechanical properties of the tissue.
498 Mariappan et al.