For centuries, physicians have used a physical examination technique known as palpation as an essential tool in clinical medicine. This enduring diagnostic method is remarkably effective because many disease processes cause large changes in tissue stiffness that can be readily easily perceptible through simple touch.
Despite its traditional place in medicine, palpation is a subjective technique, applicable only to regions of the body that are accessible to touch and limited in its ability to reveal small changes that may signal early disease. Although advanced medical imaging technologies like MRI and CT have revolutionized diagnostic medicine, traditional imaging protocols unfortunately are not capable of revealing the underlying properties of palpation: the mechanical stiffness of tissue.
To address this need, a team led by Richard Ehman, MD at Mayo Clinic, invented a technology called Magnetic Resonance Elastography (MRE)1
. Their goal was to enhance the medical standard of palpation with the diagnostic power of medical imaging by developing a practical technology capable of sensitively and quantitatively assessing the mechanical properties of soft tissue in any area of the body.
The team focused on using mechanical vibrations as a probe to measure tissue stiffness. When a shear wave propagates in a medium, its wavelength is determined by the viscoelastic properties of the material. Dr Ehman and his team set out to find a way to visualize propagating mechanical waves inside the body using MRI.
This goal was extremely challenging, because such waves only displace tissue by a few nanometers. After extensive research, the team succeeded in developing MRE – a novel MRI technique capable of reliably imaging mechanical waves inside the body with extraordinary sensitivity1
Results demonstrated that by synchronizing motion-sensitizing gradients with applied waves, cyclic motions as small as the wavelength of light could be selectively imaged in vivo, even in the presence of physiologic motion1
The Mayo Clinic team further developed novel mathematical techniques to process the wave images in order to create cross-sectional maps quantitatively displaying the stiffness of tissues and organs in the body. They first reported these discoveries in the Science journal in 19951
. After more than 10 years of further research and development involving talented teams from all over the world, MRE was validated and the technology successfully translated into clinical practice. In 2009, MRE was cleared by the US FDA and, since then, the technology has been installed on more than 1500 MRI systems around the world.
MRE technology is now provided by MRI manufacturers as an option that can be installed on virtually any conventional MRI system. The installation includes unique acquisition and processing software, as well as specialized hardware to apply vibrations to the body. In order to ensure standardization of MRE technology, the Mayo Clinic founded Resoundant, Inc. to assist MRI manufacturers in implementing their versions of MRE. The specialized hardware used in all current regulatory approved MRE systems is designed and manufactured by Resoundant.