HIGH-RESOLUTION MRI OF INTACT AND TRANSECTED RAT SPINAL-CORD

Spinal cord transection at midthoracic level leads to an immediate los s of hindlimb motor function as well as to a progressive degeneration of descending and ascending spinal cord pathways. Thoracic spinal cord in unlesioned control rats and in rats 2 to 6 months after complete m idthoracic transection were imaged in vivo using an ultrahigh-field (4 .7 T) magnetic resonance spectrometer. High-resolution spin-echo and i nversion-recovery pulse sequences were employed. In addition, the appa rent diffusion coefficients (ADCs) in longitudinal and transverse dire ctions of the spinal cord were determined. Anatomical MRI findings wer e confirmed in histological spinal cord tissue preparations. In health y spinal cord, gray and white matter were easily discerned in proton d ensity-weighted images. An infield resolution of max. 76 mu m per pixe l was achieved. In animals with chronic spinal cord transection change s in gray-white matter structure and contrast were observed toward the cut end, The spinal cord stumps showed a tapering off. This coincided with changes in the longitudinal/transverse ADC ratio. Fluid-filled c ysts were found in most cases at the distal end of the rostral stump, The gap between the stumps contained richly vascularized scar tissue. Additional pathologic changes included intramedullary microcysts, vert ebral dislocations, and in one animal compression of the spinal cord. In conclusion, MRI was found to be a useful method for in vivo investi gation of anatomical and physiological changes following spinal cord t ransection and to estimate the degree of neural degeneration. In addit ion, MRI allows the description of the accurate extension of fluid spa ces (e.g., cysts) and of water diffusion characteristics which cannot be achieved by other means in vivo. (C) 1998 Academic Press.