Magnetic resonance imaging of the central nervous system

Magnetic resonance (MR) is a powerful new imaging modality which has recently become competitive with X-ray computed tomography (CT) for imaging of the central nervous system (CNS). The advantages of MR include lack of ionizing radiation and the necessity to use iodinated contrast. MR is able to image directly in the transaxial, coronal, and sagittal planes. With appropriate pulsing sequences, MR is more sensitive than CT in the detection of early disease associated with increased water content. Included in this category are multiple sclerosis, early infarcts, small tumours, and inflammatory lesions. MR is superior to CT in the posterior fossa due to beam hardening artifacts in the latter modality. In the cord, MR is useful in the evaluation of syringomyelia, spinal dysraphism, and intramedullary tumours. Due to its increased sensitivity in the detection of early disease, MR should generally be used as the initial screening procedure in the evaluation of possible intracranial disease. Current limitations of MR include longer single slice imaging times, thicker slices, inability to use contrast agents to define blood/brain barrier breakdown, and the inability to image calcification and cortical bone. Patients on cardiac monitors or on respirators and those with intracranial aneurysm clips and cardiac pacemakers are currently excluded from MR imaging.