Applying principles of magnetic resonance and acoustics, investigators at the Mayo Clinic have developed an artificial method of "brain palpation" that may prove useful in evaluating brain injury or brain lesions.
To date, the group has demonstrated the feasibility of the system in a limited number of human volunteers. Essentially, the technique assesses the stiffness of tissues. Studies to date have shown that white matter is stiffer than gray matter.
"We do a pretty good job of assessing focal injuries to the brain," said Dr. Richard Ehman, a radiologist at the Mayo Clinic. "However, we don't do such a good job of assessing injuries that are of a more diffuse nature. This technique may help us do a better job of assessing diffuse abnormalities."
Called magnetic resonance elastography (MRE), the technique is designed to calculate changes in the mechanical properties of brain tissue in response to injury. An electromechanical vibrator creates acoustic shear waves of 75 to 125 Hz. The waves bounce off brain tissue, and data from the resulting tissue displacement, or elasticity, are captured by a standard 1.5-tesla MR imager. The information is translated into a tissue elastic modulus, which in turn can be transformed into three-dimensional renderings that demonstrate tissue response to the waves. The data also can be converted into an image called a magnetic resonance elastogram.
To date, the technique has been tested and validated in more than 40 volunteers, Ehman said. The studies have shown that normal white matter is considerably stiffer (a mean of 15.5 kPa) than gray matter (mean of 6.6 kPa). The values appear to be unaffected by age.
"We think these are the first in vivo measurements of brain elasticity," Ehman said. "This technique could provide potentially useful new parameters in neuroimaging. We think the technique could apply to the study of brain injury and to disease properties. There is a lot of interest in material properties of the brain in response to injuries and disease."
Ehman likened MRE to physical palpation used to characterize lesions located on accessible parts of the body. He noted that palpation remains a useful diagnostic tool despite the development of a several powerful, high-technology diagnostic aids.
