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Magnetoencephalography (MEG) is a technique for measuring changes in the magnetic field in and around the head created by brain activity. It can be used as a complementary assessment tool, along with other studies of brain activity and structure in the process of evaluating a patient with a suspected neurological problem. This technique is noninvasive and patients do not need to take any special steps to prepare for it.
In a magnetoencephalography study, the patient sits upright in a chair and a helmet is positioned over the head. The helmet contains a superconducting quantum interference device (SQUID) capable of picking up on very faint changes in magnetic fields. The room where the patient goes for the test is shielded to make sure the earth's magnetic field doesn't interfere with the very sensitive test. A series of snapshots of brain activity are taken.
A doctor can combine magnetoencephalography with structural imaging of the brain to generate a magnetic source imaging study, showing brain activity and the area of the brain where it originates. This can be very useful when doctors are trying to isolate a brain injury or lesion, as may occur if there are concerns about brain function after an accident or in a patient with epilepsy who experiences frequent seizures. This type of study may be a useful tool for generating more usable data when there appear to be conflicts between other studies of the brain like magnetic resonance imaging and electroencephalography.
This testing method works best when a doctor combines it with other testing to create a complete picture of what is happening inside the patient's brain. The magnetoencephalography can be conducted on the same day as other studies of the brain to collect as much information as possible about the patient's brain function and structure. Multiple tests can be used to follow up on changes or to track progress of treatments like medication.
When a doctor recommends a magnetoencephalography study, patients can ask why the study is being recommended, what other testing they should consider, and how the test will contribute to the development of a diagnosis and treatment plan. One potential use of magnetoencephalography is in generating a very targeted and accurate picture of damage in the brain so a surgeon knows exactly where to go. Sometimes, damaged areas of the brain appear superficially normal when a surgeon is working, and having clear guidelines will help the surgeon remove a brain lesion without damaging neighboring tissue or leaving parts of the lesion behind.
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