Cranial MRI

Alternative names:

head MRI scan; magnetic resonance imaging - cranial; MRI of the head; NMR - cranial; nuclear magnetic resonance - cranial

What the risks are:

There is no ionizing radiation and often no contrast dye is needed. The procedure is safe in most cases, and there are no documented side effects. However, because the effects of strong magnetic fields on a fetus are not well documented at this time, pregnant women are usually advised to avoid MRI scans.

Because the strong magnets can displace or disrupt the action of implanted metallic objects, people with cardiac pacemakers cannot be scanned and should not enter the MRI scan area. MRI also should not be used for most people with metallic objects in their bodies, such as artificial joints, inner ear (cochlear) implants, brain aneurysm clips, some artificial heart valves, and metallic foreign bodies in the eye or other body areas. MRI is usually not recommended for acute trauma situations because traction and life support equipment cannot enter the scanner area, and because of the long scan times.

Special considerations:

MRI is more accurate than CT scan or other tests for certain conditions, but less accurate for others. Disadvantages include the high cost, long duration of the scan, and sensitivity to movement. People with claustrophobia or who are confused or anxious may have difficulty lying still for the relatively long scan times. MRI is not portable and is incompatible with metallic implants, life support devices, traction apparatus, and similar equipment.

MRI is superior in most cases where differentiation of soft tissues is necessary. It can view organs without obstruction by bone and foreign bodies. It is capable of showing the tissues from multiple viewpoints and is a noninvasive way to evaluate blood flow.

A CT scan may be preferred for:

• acute trauma of the head and face
• acute (less than 72 hours) neurologic dysfunction
• early symptoms of stroke
• subarachnoid or intracranial hemorrhage (within the first 24 to 48 hours)
• skull bone disorders, disorders involving the bones of the ear