Measuring diffusion of solutes into intervertebral disks with MR imaging and paramagnetic contrast medium.

BACKGROUND AND PURPOSE Experimental studies have shown that solutes diffuse more slowly into degenerated intervertebral disks than into normal disks. A noninvasive clinical study of diffusion in intervertebral disks is not generally available. Our purpose was to evaluate contrast-enhanced MR images to study diffusion in normal and degenerated lumbar intervertebral disks. METHODS The change in signal intensity (as a proportion of baseline signal intensity) was calculated in lumbar intervertebral disks on MR images obtained before and after injection of intravenous contrast medium in 15 patients with low back pain. The intervertebral disks were classified as normal or degenerated on the basis of the MR appearance. Postoperative disks and degenerative intervertebral disks with a "high-intensity zone" were excluded. The changes in signal intensity as a proportion of baseline signal intensity were compared in degenerated disks and normal disks and the differences tested for statistical significance. RESULTS After intravenous administration of a gadolinium complex, signal intensity in normal intervertebral disks increased an average of 36% of baseline. In intervertebral disks with signs of degeneration, it increased an average of 21% of baseline. The difference was significant. CONCLUSION The study shows that diffusion into normal human lumbar intervertebral disks can be evaluated with MR imaging combined with intravenous contrast medium. With suitable MR techniques, the relationship between diffusion and disk degeneration, and the effect of trauma, drugs, and nutrition on disk degeneration can be studied noninvasively.