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Cranial MRI 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:
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 it Feels:
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.
Risks:
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.
Why this 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.
Normal Values:
No abnormalities of size or position of the brain and skull structures as viewed from any plane. No new growths or lesions. Normal blood flow and flow of CSF.
Abnormal Results:
The sensitivity of MRI depends, in part, on the experience of the radiologist. As MRI becomes more common, increasingly detailed diagnosis may be possible.
Cranial MRI may reveal disorders including: Additional conditions under which the test may be performed:
Cost:
The estimated cost is $860 to $2000.
MRI is more expensive than X-rays or CT scans, mostly because the equipment is very expensive. However, MRI may replace multiple other tests, and provides a clear image with a very low risk. The benefits often outweigh the cost of the scan.
Most insurance companies will pay for MRI scans. Some scans of certain body areas or for certain medical conditions may not be covered by all insurances, so check with the insurance company.
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
This is an illustration of the major areas of the brain. Each area has one or more specific functions.
MRI stands for magnetic resonance imaging. It is a relatively new technology that allows imaging of the interior of the body without using X-rays or other types of ionizing radiation. An MRI scan is capable of showing fine detail of different tissues. Its use is rapidly increasing while the use of standard X-rays has decreased.
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