Based on x-rays; visual “slices” through body part showing tissue density. Gray scale of display from black (low density, e.g., fluid) to white (high density, e.g., bone).

Intravenous iodinated contrast agents enhance differences in tissue density, show vascular structures, reveal areas of blood-brain barrier breakdown. Contraindications to using contrast in CT studies include renal disease, allergy to iodine, shellfish.

CT faster and less expensive than MRI. CT preferred for imaging bone, calcium, acute hemorrhage. Major limitation: posterior fossa poorly visualized.

MRI now gold standard for identifying intracranial or spinal lesions.

Spiral technique used to obtain serial scans following injection of intravenous contrast bolus; then 3D reconstruction performed. Used to image vascular anatomy, pathology (e.g., aneurysms, stenosis).

Repeated imaging of same brain region during rapid intravenous bolus contrast injection to assess brain perfusion. Can be quick screening test for acute ischemia in major vascular territories.

Superior to CT for most purposes. Images based on behavior of protons in various tissues when exposed to a strong magnetic field; brightness or darkness depends on tissue fat and water content.