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SCANS OR TESTS DESIGNED TO DETEC...

Posted Aug 23 2008 3:08pm
SCANS OR TESTS DESIGNED TO DETECT ABNORMALITIES WITHIN THE BRAIN



Electroencephalogram (EEG)



An EEG records the electrical activity of your brain via electrodes affixed to your scalp. People with epilepsy often have changes in their normal pattern of brain waves, even when they're not having a seizure.

To prepare for an EEG, avoid elaborate hair styling, metallic hair spray or greasy hair dressing. Refrain from caffeine for six hours before the test. The procedure itself is painless and usually lasts about 30 minutes. However, it can take as long as an hour to place the electrodes on your scalp.

In some cases, your doctor may recommend video-EEG monitoring. This can be helpful because it allows your doctor to compare — second by second — the behaviors that occur during a seizure with your EEG pattern from exactly that same time. This helps your doctor pinpoint exactly where your seizures originate, which aids treatment decisions.

Video EEGs are expensive because you usually must stay at the testing facility for several days. The EEG electrodes stay attached for that entire time, and you are videotaped continuously.



Computerized tomography (CT)



Using special X-ray equipment, CT machines obtain images from many different angles and join them together to show cross-sectional images of your brain and skull. CT scans can reveal abnormalities in brain structure, including tumors, cysts, strokes or tangled blood vessels. This helps your doctor rule out other potential causes of your seizures.

To prepare for a CT scan of your head, you should remove such things as earrings, eyeglasses, dentures and hairpins. You may need to have an intravenous (IV) line inserted if your test requires the injection of a contrast material — which makes abnormalities easier to see. During the test, you will lie on a table that slides into the CT machine. Depending on the number of images needed, the scan can take between two and 20 minutes. The procedure is painless.



Magnetic resonance imaging (MRI)



An MRI machine uses radio waves and a strong magnetic field to produce detailed images of your brain. Like CT scans, MRIs can reveal brain abnormalities that could be causing your seizures. Dental fillings and braces may distort the images, so be sure to tell the technician about them before the test begins.

During the test, you will lie on a padded table that slides into the MRI machine. Your head will be immobilized in a brace, to improve precision. The test is painless, but some people experience an uncomfortable feeling similar to claustrophobia inside the MRI machine's close quarters. If you think you may have a problem like this, your doctor can prescribe anti-anxiety medications beforehand.

A special type of MRI — called functional MRI (fMRI) — can measure the small metabolic changes that occur when a part of your brain is working. An fMRI can record which areas of your brain are working when you perform certain tasks, such as rubbing a block of sandpaper or answering simple questions.

Doctors know the general areas of the brain responsible for such tasks as thought, speech, movement and sensation, but the precise locations vary by individual. An fMRI can identify the locations of these critical functions so that your doctor can determine if epilepsy surgery would be a safe option for you.



Positron emission tomography (PET)



PET scans use injected radioactive material to help visualize active areas of the brain. The radioactive material is tagged in a way that makes it attracted to glucose. Because the brain uses glucose for energy, the parts that are working harder will be brighter on a PET image.

After the radioactive material is injected, it will take between 30 and 90 minutes for the substance to accumulate in your brain tissue. During this waiting period, you will be asked to rest quietly and not talk or move around much. The actual scan takes 30 to 45 minutes. The amount of radioactive material used in the test is very small, and its glucose-binding activity in the brain lasts only a short period of time.



Single-photon emission computerized tomography (SPECT)



This type of test is used primarily in people being evaluated for epilepsy surgery when the area of seizure onset is unclear on MRIs or EEGs. SPECT imaging requires two scans — one during a seizure and one 24 hours later. Radioactive material is injected for both scans and then the two results are compared. The area of the brain with the greatest activity during the seizure can be superimposed onto the person's MRI, to show surgeons exactly what portion of the brain should be removed.



Source: mayoclinic.com





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