Pediatric Neuroscience Pathways Fall 2012 - Cleveland Clinic

MEG is a measure of the magnetic fields caused by neuronal
activation. The instrument uses no X-ray radiation, generates no
magnetic fields and requires no injections. The child simply lies
quietly on a bed with his or her head resting in a special helmet.
meg’s imaging capabilities offer a high spatial resolution along with
a high temporal resolution — a combination that no other modality
for studying the brain currently offers. The flow of electrical current
through any conductor produces a magnetic field, which can then
be recorded using sensitive magnetic sensors. Because the strength
of the magnetic field produced by the brain is so small, very
specialized instrumentation is required to pick up the signal. these
sensing systems consist of small, high-resolution coils coupled to
Pediatric ePilePsy
Magnetoencephalography for Localization of Epileptogenic Sources in Children
Patricia Klaas, PhD; Richard Burgess, MD, PhD; and John Mosher, PhD
cleveland clinic began using magnetoencephalography (meg) in 2008 to aid in localizing epileptogenic sources.
the procedure has been used with adults and children who have intractable epilepsy.
Case Study: MEG Paves the Way for Successful Epilepsy Surgery
A MEG was recorded at Cleveland Clinic of a 10-year-old boy with
medically refractory epilepsy with daily seizures. video eeg evaluation
suggested that the seizures arose from the left side of the brain
but did not provide further localizing information. mri and neurological
examination were normal. ictal sPect (single photon emission
computed tomography) and interictal FDG-PET (fluorodeoxy-glucosepositron
emission tomography) were not helpful.
meg showed interictal epileptiform discharges from a restricted
location in the deep gray matter of the posterior insula and inferior
parietal cortex (Figure 1). all the interictal spikes were estimated to
Time: 145596.0–146098.0 ms
Grad: -400.0–400.0 fT/cm
Scalebars: 200 ms, 200 fT/cm, 1000 fT
t=14583.9 ms
Copyright © 2010 The Cleveland Clinic Foundation. All rights reserved.
Figure 1
devices called superconducting quantum interference devices
(SQUIDs), which must operate very close to absolute zero temperatures
in order to achieve superconductivity. approximately 300 are
arrayed around the head in a dewar containing liquid helium to
provide whole-head coverage with high resolution. By analyzing the
patterns of the signals recorded by all these sensors, the location,
strength and orientation of the sources can be inferred.
meg recordings are done both spontaneously and in response to
specific external stimuli. MEG technology is similar to the electroencephalogram
(EEG) in that it can record function over time. MEG,
however, has a higher source resolution than EEG, its recordings are
originate from the same region (Figure 2). careful scrutiny of the
MRI in the region identified by the MEG revealed a subtle blurring
of the gray-white border in the deep parietal lobe (Figure 3).
Placement of intracranial electrodes, at 11 years of age, was
guided by the results from the meg and mri. Based on the results
from intracranial recording, it was possible to perform a limited
resection of the seizure focus, sparing language and motor cortex
(Figure 4). At 13 years of age, the boy remained free of seizures
on reduced antiepileptic medication. In this case, MEG was very
helpful in identifying the focal epileptogenic zone so that the child
could have successful epilepsy surgery.
14 Pediatric NeuroscieNce Pathways | 2012 – 2013
Figure 2
Figure 3 Figure 4