Diffusion Tensor Magnetic Resonance Imaging, or DT-MRI, is a technology that measures the random motion of hydrogen atoms within water molecules in all three dimensions, non-invasively, and in vivo. DT-MRI adds to conventional MRI the capability of measuring the random motion of water molecules, referred to as diffusion. Although water appears placid to the naked eye, individual water molecules are constantly in motion, colliding with each other and with other molecules in tissues at high speeds. These high-speed collisions cause the water molecules to spread out or diffuse. Diffusion causes a drop of a dye that is placed at the center of a beaker of water to slowly spread apart in a spherical pattern. Water in tissues containing a large number of fibers, like skeletal muscle, cardiac muscle, and brain white matter, diffuse fastest along the direction that the fibers are pointing in, and slowest at right angles to it. In contrast, water diffuses in a spherical pattern in tissues that contain few fibers. DT-MRI renders such complex information about how water diffuses in tissues into intricate three-dimensional representations of the tissues.
While this technology provides new information about the state of many tissues within the body, it is particularly informative when imaging fibrous tissues, such as tendons, and ligaments. The ability to measure these different rates of diffusion along different directions is one of the features that distinguish DT-MRI from other imaging methods.
DT-MRI was invented at the National Institutes of Health by Peter J. Basser, James Mattiello, and Denis LeBihan. According to Basser, DT-MRI provides novel, histological and anatomical information about tissue structure, composition, architecture, and organization. Changes in these tissue properties can often be correlated with processes that occur in development, degeneration, disease, and aging, so this method is becoming more widely applied.