APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014;
Denver, Colorado
Session F23: Invited Session: Industrial Physics Forum: The Squid at 50: Impact and Future
8:00 AM–11:00 AM,
Tuesday, March 4, 2014
Room: 505-507
Sponsoring
Unit:
FIAP
Chair: John Clarke, University of California, Berkeley, Dale Van Harlingen, University of Illinois at Urbana-Champaign
Abstract ID: BAPS.2014.MAR.F23.5
Abstract: F23.00005 : Magnetoencephalography: From first steps to clinical applications*
10:24 AM–11:00 AM
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Abstract
Author:
Risto Ilmoniemi
(Aalto University)
Magnetoencephalography (MEG), the study of femtotesla-range magnetic fields
produced by neuronal currents in the brain, originated in the 1960's. After
Baule and McFee's (Am Heart J 66:95-6,1963) measurement of the cardiac
magnetic field using induction-coil sensors, Cohen (Science 16:784-6, 1968)
used a similar multi-turn coil to detect the brain's alpha rhythm. The
introduction of the superconducting quantum interference device (SQUID) by
Zimmerman et al. (J Appl Phys 41: 1572-80) improved the sensitivity of
magnetic sensing by several orders of magnitude, making MEG practical. The
SQUID enabled the unaveraged recording of spontaneous brain rhythms (D.
Cohen, Science 175:664-6, 1972) as well as evoked magnetic fields (Brenner
et al., Science 190:480-2, 1975; Teyler et al., Life Sci 17:683-91, 1975).
Subsequently, a large number of evoked-field variants were demonstrated.
The main benefit of MEG is its ability to locate electrical activity in the
brain at high temporal resolution. For practical work, we need large arrays
of highly sensitive SQUIDs; such arrays were first built in the 1990's
(Knuutila et al., IEEE Trans Magn 29:3315-20, 1993). While the intrinsic
spatial accuracy of locating sources with well-calibrated large sensor
arrays is better than one millimeter, uncertainties in determining the
location and geometry of the cortex with respect to the array may lead to
source-location errors of 5--10 mm or more. These errors could be reduced to
1 mm if one could obtain the structural image of the brain with the same
sensors that are used for MEG and if the conductivity geometry of the head
would be accurately known. This may indeed be possible if MRI is recorded
with SQUIDs (McDermott et al., PNAS 21:7857-61, 2004) concurrently with MEG
(Zotev et al., J Magn Reson 194:115-20, 2008), especially if large arrays
are developed (Vesanen et al., Magn Reson Med 69:1795-1804, 2013); the
conductivity distribution of the head might be possible to determine with
current-density imaging (Nieminen et al. Magn Reson Imaging, 2013).
MEG has established itself as a standard tool in human neuroscience
(Hamalainen et al., Rev Mod Phys 65:413-97, 1993). It is used increasingly
in clinical applications such as in locating motor or language areas prior
to brain surgery or in determining characteristics of epileptic activity of
patients.
*Support from the Academy of Finland is acknowledged.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2014.MAR.F23.5