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Magnetic Resonance Imaging (MRI) of the Brain
What is the test?MRI is a noninvasive technique for visualizing many different body tissues. Unlike x-rays, MRI does not use any radiation. Instead, it uses radio waves, a large magnet, and a computer to create images.As with a CT scan, which does use x-rays, each MRI picture shows a different "slice," or cross-section, of the area being viewed. Because these slices usually are spaced about a quarter-inch apart, your doctor can get a detailed representation of a particular area. An MRI of the brain can identify tumors and areas of brain damage caused by a stroke or another neurological condition. How do I prepare for the test?Tell your doctor if you have a pacemaker, artificial hip, or any metal pins, plates, screws, or surgical staples. The magnet used in an MRI is so strong that it can interfere with pacemakers and pull on some metal objects implanted in the body. If you know you have an implant, or are concerned, discuss the issue with your doctor, as other options may exist. (Some pacemakers, for example, can be reprogrammed prior to an MRI so that they are not disrupted.) An IV is inserted into a vein if the particular scan you're having requires a dye to make areas of inflammation or abnormality easier to detect. This dye is called gadolinium, and is different from the contrast dye used for x-rays or CT scans. Before undergoing the scan, remove metal objects such as belt buckles or watches, which could dislodge in the presence of the magnet and hurt you. What happens when the test is performed?The MRI is a large machine with a circular tunnel built through it, like the hole of a donut. You lie on your back on a narrow table that can be moved back and forth into the tunnel.When MRI scans are taken, expect to hear some loud noises from the machine. Some MRI departments offer earplugs or a stereo headset to block this noise. A technician moves your table using an automatic control.When each picture is taken, he or she asks you to hold your breath for a few seconds. If you need to have dye injected through the IV, this is usually done halfway through the scanning. An MRI typically takes 30-90 minutes. It can be difficult if you are uneasy in tight spaces or have trouble lying flat for that amount of time. If you think you might have trouble getting through the procedure, talk to your doctor beforehand and discuss whether an anti-anxiety medicine might help. After the test is done, you can go about your normal activities. What risks are there from the test?There are no risks from the MRI scan unless you have a pacemaker or metal implants from previous surgeries. The MRI causes no side effects, and allergic reactions to the dye are rare. Must I do anything special after the test is over?No. How long is it before the result of the test is known?MRI images are often recorded on film; if so, it will take at least an hour for the MRI department to develop the images and additional time for a doctor to examine and interpret them. If the images are stored in and displayed by a computer, there is no time required to develop the images, although the doctor's interpretation still takes time. You can probably get preliminary results within a day or two, but the complete results might take four to seven days. |
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