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Mark McManis, PhD, prepares patient for a MEG scan.

Surgical treatment of neurological conditions and brain tumors has typically been impeded by the inability to precisely pinpoint the sensory functions affected by a lesion. While fMRI and EEG helped associate structure and some level of activity, neurological mapping during surgery has long been the primary way to determine function, until now. In an effort to take better care of children with complex brain problems, Le Bonheur Children’s Medical Center opened a magnetoencephalography (MEG) laboratory last fall, making it the third pediatric hospital in the country to have this technology.

MEG is a non-invasive imaging technique that measures the magnetic fields produced by intracranial electrical currents using highly sensitive external sensors called superconducting aluminum quantum interference devices (SQUIDs). These magnetic fields indicate precise locations for particular neuronal functions. MEG is primarily used among children with neurological conditions such as epilepsy and brain tumors to chart brain function before surgery, thus determining the best surgical route to keep functions in tact. The MEG, an 18,000-pound machine, is the first diagnostic imaging technology approved in the United States to perform functional mapping of the eloquent cortices (hearing, sensory, motor, language and vision) in patients with brain lesions.

Dr. James Wheless, director of Le Bonheur’s Neuroscience Institute and Comprehensive Epilepsy Program, and division chief of pediatric neurology at the University of Tennessee Health Science Center, offered this analogy: “Having MEG is like taking the neuroscience program from not even being in the first 64 to jumping to the final four,” he said. “It puts Le Bonheur and Memphis on the map.”

Mark McManis, PhD, serves as technical director of the MEG clinic. He explained that the MEG has 248 of the most sensitive devices available for recording brain activity. Because of the sensors’ extreme sensitivity, the room must be shielded from magnetic fields that can interfere with MEG measurements, including those created by Earth, urban noise such as power lines, and noise from other organs. Where Earth’s magnetic field is 30 to 60 microTesla and urban noise is 1/100th of the earth’s field, the brain signals picked up by the SQUID sensors are at a tiny one quadrillionth of a Tesla.

“If I am doing the math correctly,” McManis deduced, “that is 1 billionth the strength of the Earth’s field.”

The MEG laboratory is located on the first floor of the hospital in a room protected by layers of copper and mu metal, a nickle-aluminum alloy.

Unlike an MRI or a PET scan, MEG will allow physicians to see changes in brain activity in real time and effectively generate a map of a child’s individual brain function. The sensors are put over the head and ears like a helmet, while the patient lies on a bed. Scans can take up to an hour and a half, depending on what information is needed. While patients undergo scanning, McManis and his team watch the computer which creates dots in precise locations in the brain that indicate where an electrical impulse originated. The information derived from MEG is superimposed onto anatomical images, such as fMRI, providing both the structure and function of the brain, using real time to track function as it happens.

“Instead of looking at the end result, we’re following the signal all the way through the brain,” explained Wheless.

MEG makes it possible to do functional mapping before surgery, instead of when the skull is open, giving immediate clinical application to everyone on the neurological team including scientists, neurologists and neurosurgeons.

The ability to assess and think ahead offers even greater benefit to patients because they’ll have the chance to become fully aware of the implications of surgery. MEG allows the patient who already requires surgery a safer procedure, explained Wheless, while it also opens up the option for surgery to patients who were formerly considered ineligible.

“Finally it’s the patient’s decision to make,” added McManis about surgical planning. “They’ll know exactly what’s going to happen and the symptoms.”

The MEG laboratory will also be used to develop research protocols for mapping children’s brains with developmental disorders such as autism, ADHD and dyslexia. Neuropsychologists have long struggled with accurately determining the relationship between the brain and its ability to perform cognitive tasks such as speaking, reading and listening.

The real-time applications of MEG illustrate what is happening sequentially, showing changes in the brain that can be detected the moment a child is asked to speak, which helps scientists view, “which parts of the brain are switching attention from here to there,” McManis explained.

Since the installation of the MEG last fall, Wheless has been scheduled for talks across the globe. He’ll be in Germany to speak about the laboratory this month. The bigger picture of having the MEG laboratory is that, he said, “it sends the signal that Le Bonheur is establishing themselves as a high level neuroscience center of excellence.”

The Urban Child Institute donated $2.9 million to Le Bonheur to purchase the MEG.



April 2008

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