SPINAL-CORD NEURAL ANATOMY IN RATS EXAMINED BY IN-VIVO MAGNETIC-RESONANCE MICROSCOPY

Background and Objectives. Magnetic resonance microscopy (MRM) is a te chnique that is worthwhile for anesthesiologists because it allows spi nal cord and plexus anatomy to be visualized three dimensionally and f ollowed over time in the same animal. For example, the long-term effec t of indwelling intrathecal or plexus catheters can be studied in situ , and convective and diffusive forces within intrathecal, epidural, or nerve sheath spaces can be investigated. Further, diffusion-weighted MRM, which measures an ''apparent diffusion coefficient'' (ADC), can b e used to track the presence of ischemia, hypoperfusion, or cytotoxic edema. This study investigates problems associated with the use of in vivo MRM for spinal cord and peripheral nerve studies in the rat. Meth ods. Twenty-one anesthetized female Fisher CDF rats were used. Group 1 (n = 7) was used for anatomic three-dimensional studies. Groups 2 (n = 4), 3 (n = 4), and 4 (n = 6) were used for measurements of the ADC. Group 2 served as controls, group 3 received lumbar intrathecal cathet ers, and group 4 received cervical intrathecal catheters. Results. Cer vical spine, lumbar spine, and spinal nerves and ganglia were accurate ly visualized with MRM. As a rule, spinal cord gray and white matter w ere better demonstrated using diffusion-weighted proton stains. By con trast, T2-weighted proton staining superiorly demonstrated structures surrounding the spinal cord. In groups 3 and 4, indwelling-intrathecal catheters did not affect the spinal cord ADC, indicating normal blood flow and no cytotoxic edema. Contrast studies revealed nonhomogeneous distribution of contrast predominately in the lateral and ventral int rathecal space. Conclusions. Three-dimensional diffusion-weighted MRM displays cervical and lumbar spine anatomy accurately in vivo. Apparen t diffusion coefficients measurements are feasible in rat cervical spi nal cord with intrathecal catheters. Spinal cord ADCs are unaffected b y intrathecal catheters, indicating normal spinal cord perfusion.