Emerging Imaging Techniques for Disease Diagnosis and Therapy

11.18.2008 Magnetic Resonance Elastography SPEAKER: Richard L. Ehman, MD: Mayo Clinic MODERATOR: Ferenc Jolesz, MD: BWH, HMS, CIMIT

Forum Summary

Magnetic resonance elastography (MRE) is an emerging technique used to quantitatively image the elastic properties of tissues.  Unlike most other imaging techniques, MRE measures a physical property that is directly affected by disease.  For decades, physicians have used palpitation to diagnose problems in many areas of the body including the thyroid, breast, and prostate.  The usefulness of palpitation as a diagnostic tool demonstrates that changes in tissue elasticity can be an important indicator of disease.  MRE promises to be a valuable new technique because it quantifies elasticity and because it allows doctors to examine the elasticity of tissues deep within the body.

The technique itself involves imaging tissue using magnetic resonance imaging (MRI) while a dynamic stress is being applied.  The dynamic stress is produced by one or more mechanical drivers and generates waves within the tissue.  The essential concept behind the technique is the inverse relationship between the speed of wave propagation and the elasticity of the tissue.  Thus, tissue elasticity can be inferred from the speed of wave propagation, which can be measured using MRI.  Calculating the elasticity (or stiffness) from the propagation speed involves an inversion algorithm, and this inversion algorithm can be designed to filter out signals from interfering waves.

The initial application of MRE has been to liver disease.  Chronic liver disease is a leading cause of death worldwide, and every year, millions of people develop liver fibrosis that can lead to irreversible cirrhosis.  If detected early, the development of fibrosis can be stopped and even reversed; but up until now, the only way to detect fibrosis has been to perform a liver biopsy, a potentially risky procedure.  Now, however, it seems that MRE may be able to detect early-stage fibrosis non-invasively.  As the amount of fibrosis in the liver increases, the stiffness of the liver increases.  In fact, early tests using MRE indicate that changes in elasticity precede the onset of fibrosis, suggesting that traditional theories about the development of fibrosis need to be revised.

In the future, researchers hope to use MRE to image other parts of the body.  It might eventually be used, for example, to detect breast cancer; or it might be used to study changes in the brain associated with neurodegenerative disease.  It could even be used to differentiate between malignant and benign tumors, for it has been shown that malignant tumors are usually stiffer than benign ones.  To improve the technique, researchers plan to explore new drivers and inversion algorithms.  Faster three-dimensional wave imaging techniques are also being sought.

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