Cranial MRI
Alternative names:
head MRI scan; magnetic resonance imaging - cranial; MRI of the head; NMR - cranial; nuclear magnetic resonance - cranial
How the test is performed:
The MRI scanner is in an area that has been shielded from outside magnetic fields. You lie on a narrow table that can slide inside a large tunnel-like tube within the scanner. The scanner creates a magnetic field around you, then pulses radio waves at the tissues in question. Several sets of images are usually required, each taking from 2 to 15 minutes. The complete scan takes about 1 hour; some scans take more than 90 minutes.
How to prepare for the test:
No preparatory tests, diets, or medications are usually needed. You may be asked to fast for 4 to 6 hours prior to the scan. You must sign a consent form before the scan.
Because of the strong magnets, no metallic objects are allowed into the room. Items such as jewelry, watches, credit cards, and hearing aids, can be damaged by the strong magnets. Pins, hairpins, metal zippers, and similar metallic items can distort the images. Frequent exposure to ferrous metals (such as a sheet metal worker has) may make MRI difficult. A hospital gown may be recommended, or you may be allowed to wear "sweats" or similar clothing without metal fasteners. Take out removable dental work just prior to the scan.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel:
There is no pain. The magnetic field and radio waves are not felt. The primary discomfort is the claustrophobic feeling that some people experience from being inside the scanner. The table may be hard or cold, but you can request a blanket or pillow.
The machine produces loud thumping and humming noises. Ear plugs are usually given to reduce the noise.
A technologist observes you during the entire procedure and may enter the room to speak to you or may speak with you through an intercom in the scanner.
Excessive movement can blur MRI images. If you have difficulty lying still or are very anxious, you may be given a sedative. The viewing of some brain lesions may require use of an intravenous dye. There is no recovery required (unless you have been sedated). After an MRI scan, you can usually resume normal diet, activity, and medications.
Why the test is performed:
MRI provides detailed pictures of brain and nerve tissues from multiple planes without obstruction by overlying bone. In fact, approximately 90% of all MRI scans are for cranial or spine disorders.
MRI is the procedure of choice for most brain disorders. MRI is particularly useful in brain and neurologic disorders, because it can clearly show various types of nerve tissue. It provides clear pictures of the brainstem and posterior brain, which are difficult to view on CT scan. It is also useful for the diagnosis of demyelinating disorders (disorders such as multiple sclerosis that cause destruction of the myelin sheath of the nerve).
MRI is a noninvasive procedure that can evaluate blood flow and the flow of cerebrospinal fluid (CSF). MRI can distinguish tumors or other lesions from normal tissues. MRI is sometimes used to avoid the dangers of angiography or of repeated exposure to radiation.
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