Diffusion anisotropy MRI for quantitative assessment of recovery in injured rat spinal cord

Spinal cord injury and its devastating consequences are the subject of inte nsive research aimed at reversing or at least minimizing functional loss, R esearch efforts focus on either attenuating the post-injury spread of damag e (secondary degeneration) or inducing some regeneration. In most of these studies, as well as in clinical situations, evaluation of the state of the injured spinal cord poses a serious difficulty. To address this problem, we carried out a diffusion-weighted MRI experiment and developed an objective routine for quantifying anisotropy in injured rat spinal cords. Rats were subjected to a contusive injury of the spinal cord caused by a controlled w eight drop. Untreated control rats were compared with rats treated with T c ells specific to the central nervous system self-antigen myelin basic prote in, a form of therapy recently shown to be neuroprotective, After the rats were killed their excised spinal cords were fixed in formalin and imaged by multislice spin echo MRI, using two orthogonal diffusion gradients. Appare nt diffusion coefficient (ADC) values and anisotropy ratio (Al) maps were e xtracted on a pixel-by-pixel basis. The calculated sum of Al values (SAl) f or each slice was defined as a parameter representing the total amount of a nisotropy. The mean-Al and SAI values increased gradually with the distance from the site of the lesion. At the site itself, the mean-Al and SAI value s were significantly higher in the spinal cords of the treated animals than in the controls (P = 0.047, P = 0.028, respectively). These values were co nsistent with the score of functional locomotion. The difference was also m anifested in the Al maps, which revealed well-organized neural structure in the treated rats but not in the controls. The SAI values, Al histograms, a nd Al maps proved to be useful parameters for quantifying injury and recove ry in an injured spinal cord. These results encourage the development of di ffusion anisotropy MRI as a helpful approach for quantifying the extent of secondary degeneration and measuring recovery after spinal cord injury. Mag n Reson Med 45:1-9, 2001. (C) 2001 Wiley-Liss, Inc.