The parenchymal CT myelogram: in vivo imaging of the gray matter of the spinal cord.

Past attempts to visualize the internal structure of the spinal cord in vivo have been hampered by many factors, including the small size of the cord, the dense bony investiture of the spine, and the similarities of tissue densities from one region to another within the cord. Delayed CT is the imaging technique currently being used at our institution as an adjunct to iopamidol myelography to visualize the deep gray matter of the cord. This visualization is achieved by a poorly understood differential gray/white-matter enhancement, possibly due to either a shielding effect of the white matter as it envelops the gray matter, a differential absorption rate between gray and white matter, or a greater rate of reabsorption of contrast by the more highly vascularized gray matter. This method is not being advocated as a primary diagnostic technique due to the lack of reliability in providing successful results from section to section, from patient to patient, and from one time period of delay to the next. Instead, it is an initial attempt to image the basic, intrinsic structure of the spinal cord in vivo, which may herald a valuable advance in imaging methodology.