Rationale and clinical indications for contrast agents in MR imaging of the brain and spine.

This presentation explores clinical indications, limitations, and the scientific rationale for use of gadolinium contrast agents in MR imaging of the brain and spine. Enhancement of abnormal CNS tissues is related to structure and function of the blood-brain barrier under pathologic conditions, the prototype of which is tumor angiogenesis. Gadolinium administration can improve the diagnostic sensitivity of intracranial MR imaging, facilitating detection of leptomeningeal or ependymal disease spread and metastases. Moreover, use of contrast often provides greater diagnostic specificity by virtue of the presence and, in many cases, the absence of enhancement. This is particularly helpful in distinguishing metastases from other potential causes of high signal intensity on unenhanced spin-echo (SE) images. In addition to improving diagnosis of neoplasia, gadolinium use is often necessary to demonstrate most cranial neuropathies and to differentiate herniated disc from epidural fibrosis in the failed-back surgery syndrome. Advanced techniques that exploit gadolinium's properties (e.g., MR angiography, perfusion MR imaging) or increase its diagnostic effectiveness (e.g., fat suppression in the postoperative spine) are treated.