Computed tomography Computed Tomography (CT) In CT, an x-ray source and x-ray detector housed in a doughnut-shaped assembly move circularly around a patient who lies on a motorized table that is moved through the machine. Usually, multidetector... read more (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, given IV, helps detect abnormal structural lesions such as brain tumors Overview of Intracranial Tumors Intracranial tumors may involve the brain or other structures (eg, cranial nerves, meninges). The tumors usually develop during early or middle adulthood but may develop at any age; they are... read more , brain abscesses Brain Abscess A brain abscess is an intracerebral collection of pus. Symptoms may include headache, lethargy, fever, and focal neurologic deficits. Diagnosis is by contrast-enhanced MRI or CT. Treatment is... read more , and some vascular anomalies, including arteriovenous malformations. With an intrathecal agent, CT can outline abnormalities encroaching on the brain stem, spinal cord, or spinal nerve roots (eg, meningeal carcinoma, herniated disk Cervical Herniated Nucleus Pulposus Herniated nucleus pulposus is prolapse of an intervertebral disk through a tear in the surrounding annulus fibrosus. The tear causes pain due to irritation of sensory nerves in the disk, and... read more ) and may detect a syrinx Syrinx of the Spinal Cord or Brain Stem A syrinx is a fluid-filled cavity within the spinal cord (syringomyelia) or brain stem (syringobulbia). Predisposing factors include craniocervical junction abnormalities, previous spinal cord... read more in the spinal cord. However, an intrathecal agent is rarely used today since the availability of MRI.
CT angiography using a contrast agent can show the cerebral blood vessels, obviating the need for MRI or conventional angiography.
Adverse effects of contrast agents Radiographic Contrast Agents and Contrast Reactions Radiopaque contrast agents are often used in radiography and fluoroscopy to help delineate borders between tissues with similar radiodensity. Most contrast agents are iodine based. Iodinated... read more include allergic reactions and contrast nephropathy.