CT provides rapid, noninvasive imaging of the brain and skull. CT is superior to magnetic resonance imaging (MRI) in visualizing fine bone detail in (but not the contents of) the posterior fossa, base of the skull, and spinal canal.
Noncontrast CT is used to rapidly detect acute hemorrhage and various gross structural changes without concern about contrast allergy or renal failure.
A radiopaque contrast agent helps detect brain tumors and brain abscesses. With an intrathecal agent, CT can outline abnormalities encroaching on the brain stem, spinal cord, or spinal nerve roots (eg, meningeal carcinoma, herniated disk) and may detect a syrinx in the spinal cord.
CT angiography using a contrast agent can show the cerebral blood vessels, obviating the need for MRI or angiography.
Adverse effects of contrast agents include allergic reactions and contrast nephropathy.