MRI of the head

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Brain

MRI of the head

Definition:

An MRI of the head is a non-invasive procedure that uses powerful magnets and radio waves to construct clear, detailed pictures of brain tissues.

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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 (nuclear magnetic resonance imaging) -- 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 is easily 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. These errors are called artifacts.

Alternative Names:
Nuclear magnetic resonance - cranial; Magnetic resonance imaging - cranial; Head MRI scan; MRI - cranial; NMR - cranial; Cranial MRI
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.

You will 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. 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 1 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: