HIGH-RESOLUTION MAGNETIC-RESONANCE-IMAGING OF EXPERIMENTAL SPINAL-CORD INJURY IN THE RAT

THE ABILITY OF magnetic resonance imaging (MRI) to display the anatomic changes after spinal cord injury in the rat were examined in postmortem specimens. With the clip compression technique, acute spinal cord injuries of three grades of severity were produced in adult male rats. One hour after injury, during which time physiological parameters were measured and maintained within the normal range, the rats were killed by transcardiac perfusion of formalin. The vertebral column containing the cervical and upper thoracic segments was excised and, after further formalin fixation, 20 contiguous MRI scans centered on the injury site were obtained using a spin-echo imaging sequence. The volume of signal acquisition for each image was 15 X 15 X 1.0 mm thick. The spinal cords were then removed from the vertebral column, sectioned, and stained for histological examination. Ten-micrometer serial sections of each cord were examined microscopically. MRI scans and microscopic sections at comparable levels were examined to determine the quality of anatomical detail and spatial resolution of the MRI scans. MRI scans with resolution of about 75-mu-m per pixel edge were obtained. At the site of injury, there was disruption of the normally well demarcated gray-white interface and variable areas of low signal intensity. Because of the resolution achieved, it was possible to determine that these low signal intensity areas were post-traumatic hemorrhages. Indeed, hemorrhages with dimensions of the order of 100-mu-m were detected on the MRI scans. Furthermore, by examining the serial sections of the cord, the extent of the injury along the cord could be determined. Increasing injury severity resulted in increased gray-white disruption, increased number and size of the hemorrhages, and an increased volume of cord affected. These results demonstrate that high-resolution MRI may be used to quantify post-traumatic changes at the microanatomical level in a small animal model of experimental spinal cord injury. The study provides the basis for the development of techniques for high-resolution MRI of the spinal cord in live animals.