NMR - cranial
Key points
- An MRI of the head is a non-invasive procedure that uses powerful magnets and radio waves to construct pictures of the clear, detailed pictures of brain tissues.
- Since MRI makes use of radio waves very close in frequency to those of ordinary FM radio stations, the scanner must be located within a specially shielded room to avoid outside interference.
- No preparatory tests, diets, or medications are usually needed.
- The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experiences, and level of trust.
Alternative names
Nuclear magnetic resonance - cranial; Magnetic resonance imaging - cranial; Head MRI scan; MRI - cranial; MRI of the head; Cranial MRI
Definition
An MRI of the head is a non-invasive procedure that uses powerful magnets and radio waves to construct pictures of the clear, detailed pictures of brain tissues.
Unlike conventional radiography and computed tomography (CT), which make use of potentially harmful X-rays passing through a patient to generate images, MRI imaging is based on the magnetic properties of atoms. A powerful magnet generates a magnetic field roughly 10,000 times stronger than the Earth's. A very small percentage of hydrogen atoms within the body will align with this field.
The "nuclear" in the original name (now seldom used) refers to the proton in the nucleus of the hydrogen atom and does not imply radioactivity.
When focused short radio wave pulses are broadcast towards the aligned hydrogen atoms in tissues of interest, they will return a signal of their own. The subtle differences in that signal from dissimilar tissues enables the MRI to differentiate between various organs, and potentially, provide contrast between benign and malignant (cancerous) tissue.
Any imaging plane, or "slice", can be projected, and then stored in a computer or printed on film. MRI can easily be performed through clothing and bones. However, certain types of metal in or around the area of interest can cause significant errors in
the reconstructed images. (The errors are called artifacts.)
How the test is performed
Since MRI makes use of radio waves very close in frequency to those of ordinary FM radio stations, the scanner must be located within a specially shielded room to avoid outside interference.
The patient will be asked to lie on a narrow table which slides into a large tunnel-like tube within the scanner. In addition, a small device may be placed around the head to be studied. This is special body coil which send and receive the radio wave pulses, and is designed to improve the quality of the images.
If contrast is to be administered, intravenous access will be placed, usually in a small vein of the hand or forearm.
A technologist will operate the machine and observe you during the entire study from an adjacent room. Several sets of images are usually required, each taking from 2 to 15 minutes. A complete scan may take up to one hour or more. Newer scanners with more powerful magnets utilizing updated software and advanced sequences may complete the process in less time.
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.
Written and revised by
David Cohen, M.D.
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