what’s the difference between eeg and meg in practice?
TRANSCRIPT
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International Workshop on Advanced Epilepsy TreatmentMarch 28-30, 2009, Kitakyushu, Japan
(Invited Talk #2)
What’s the difference between EEG and MEG
in practice?
Nobukazu Nakasato, MD, PhD
Department of Neurosurgery, Kohnan Hospital & Tohoku University, Sendai, Japan
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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Dipole Simulator (BESA)EEG MEGDipole
Number:Single
Position: Center
Orientation:Radial
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EEG MEGDipole
Dipole Simulator (BESA)
Number:Single
Position: Vertex
Orientation:Radial
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Dipole Simulator (BESA)EEG MEGDipole
Number:Single
Position: Vertex
Orientation:Tangential
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Dipole Simulator (BESA)EEG MEGDipole
Number:Single
Position: Central
Orientation:Tangential
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Dipole Simulator (BESA)EEG MEGDipole
Number:Single
Position: Temporal
Orientation:Tangential
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Dipole Simulator (BESA)EEG MEGDipole
Number:Single
Position: Temporal
Orientation:Oblique
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Dipole Simulator (BESA)Forward Calculation EEG MEGDipole
Number:Single
Position: Temporal
Orientation:Oblique
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MEG System “Model-2020”
✓ More-channels and higher density✓ Wider coverage including face and neck✓ Shorter distance between sensor and scalp
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Dipole Simulator (BESA)Inverse Problem
No unique solution in inverse problem ... (Helmholtz)
EEG MEGDipole
Number:Single
Position: Temporal
Orientation:Oblique
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Separation of Two Signals
DIPOLE EEG MAP MEG MAP
L+R L+R L+R
R
L
Dipole Simulation by BESA 5.0
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MEG in Sendai, since 1988
1988
1993
1999
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EEG-MEG powered by ... (2008)
Simultaneous Recording Combined Analysis
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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Somatosensory Evoked Fields
F/48Meningioma
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Somatosensory Evoked Fields
F/48Meningioma
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Somatosensory Evoked Fields
Nakahara et al. 2004
W. Penfield
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Kimura T, Ozaki I, Hashimoto I:
Impulse propagation along thalamocortical fibers can be detected magnetically outside the human brain.
J Neurosci 28: 12535-8, 2008
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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Normal Subject
EEG MEG
Normal Subject
Auditory Evoked Response (N100)
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Skull Defect
EEG MEG
Auditory Evoked Response (N100)
Head Injury(M/41)
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Auditory Evoked Response (N100)
Head Injury(M/41)
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Practical Problems in Spontaneous EEG and MEG Activity
Signal
Source Number Unknown, usually multiple
Signal
Source Extent Unknown, usually wide
Signal Source Configuration
Unknown, usually complicatedSignal
Source StabilityUnknown, usually moving, expanding, and propagating
Noise
Environmental Noise
Yes, but may be reduced technicallyNoise
Brain Noise Yes, and hardly eliminated
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Spontaneous ActivityDetectabilityLocalizationOrientation
Summary
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Blinded Comparison of EEG and MEG
Iwasaki M, et al. 2003
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Blinded Comparison of EEG and MEG
Iwasaki M, et al. 2003
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Blinded Comparison of EEG and MEG
Iwasaki M, et al. 2003
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Blinded Comparison of EEG and MEG
Iwasaki M, et al. 2003
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Park HM, et al. 2003
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Relative ECD Location (mm) and Moment (%)
Iwasaki M, et al. 2003
Park HM, et al. 2003
E/M spikes
M spikes
Scalp EEG may overlook small tangential spikes?
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Scalp EEG may overlook small tangential spikes?
Park HM, et al. 2003
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Perilesional, Mirror and Remote Spikes in Single Cavernoma
R L R L
R L R L
R-T L-TMEG
EEG
Jin K, et al. 2007
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Perilesional, Mirror and Remote Spikes in Single Cavernoma
Jin K, et al. 2007
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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Localization: Simple & Excellent
Left leg twitch followed by 2nd-GTC(M/20)
C3
CzC4
T7
T8
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Localization: Simple & Excellent
Left leg twitch followed by 2nd-GTC(M/20)
C3
CzC4
T7
T8
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Localization: Simple & ExcellentTumor Surgery, at 5 y.o.(M/27)
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Localization: Simple & Excellent
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AT, Class-I Non-AT, Class-I Non-AT, Class-III
Localization: Propagation
Iwasaki et al. 2002
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Propagation Hypothesis: Anterior T.
Spike (-)Seizure (-)
MEGSpike Dipole
Spike (-)Seizure (-)
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Propagation Hypothesis: Non-Ant. T.
Spike (-)Seizure (-)
Spike (+)Seizure (+)
MEGSpike Dipole
MEGSpike Dipole
MEGSpike Dipole
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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Benign Childhood Epilepsy with Centro-Temporal Spikes (BECCT)
Idiopathic localization-related epilepsy
Childhood-onset
Motor and/or sensory symptom of orofacial, unilateral upper and/or lower limbs
Rare seizure attacks
Frequent spontaneous remission
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Benign Rolandic Spikes
Ishitobi M et al. 2005
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Parietal Lobe Theory(previous articles)
Benign Rolandic SpikesFrontal Lobe Theory(Ishitobi et al. 2005)
Ishitobi M et al. 2005
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Salayev KA et al. 2006
Spike Orientation Predicts ...
CentralSpike,
Posterior
Case 1: Lt PLE
CentralSpike, Posterior
Case 2: Rt PLE
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Spike Orientation Predicts ...
MedialSpike,
towardsRight
Case 3: OLE
R R
Salayev KA et al. 2006
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Spike Orientation Predicts ...
Case 4: Rt TLE
SylvianSpike,
Downward
Case 5: Lt TLE
SylvianSpike, Downward
Case 5: Lt TLE
SylvianSpike, Downward
R L
Salayev KA et al. 2006
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Spike Orientation Did Not Predict ...
Case 6: Rt TLE
SylvianSpike,
Upward
R
Salayev KA et al. 2006
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Central (Rolandic) Spike
Anterior Orientation: Frontal Side (100%)
Posterior Orientation: Parietal Side (100%)
Interhemispheric Spike
Right Orientation: Right Hemisphere (100%)
Left Orientation: Left Hemisphere (100%)
Sylvian Spike in Temporal Lobe Epilepsy
Downward Orientation: 73% of Sylvian spikes
Upward Orientation: 27% of Sylvian spikes
Spike Orientation Predicts ...
Exceptional !
Salayev KA et al. 2006
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Sex/Onset, MEG
Atypical Seizures as BECCT
Seizure Frequency (Max./Latest)
Others
1 F/2, 22 falling weekly/weekly PLE confirmed by ECoG
2 M/2, 29 consciousness loss with automatism
daily/daily
3 F/2, 3 falling and head dropping
daily/ (-) Mental retardation and behavioral problems
4 F/3, 12 posturing daily/daily
5 F/3, 5 head dropping daily/ (-) Transient graphomotor impairment
6 F/11, 23 auditory hallucinations
monthly/monthly
7 F/12, 23 auditory hallucinations
daily/daily
Sensorimotor Seizures of Pediatric Onset with Unusual Posteriorly Oriented Rolandic Spikes
Kakisaka Y. et al. 2009
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Case 1 Case 8
EEG
MEG
Kakisaka Y. et al. 2009
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Case 5
Kakisaka Y. et al. 2009
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What’s the difference between EEG and MEG in practice?
IntroductionTheory & Practice
Evoked ResponsesSingle SourceDual Source
Epileptic SpikesDetectabilityLocalizationOrientation
Summary
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What’s the difference between EEG and MEG in practice?
Spike Detectability
Theory: EEG detects radial and tangential currents, while
MEG detects Tangential current only.
Practice: Some are found in EEG only, MEG only, or both.
Spike Localization
Theory: No unique solution in inverse problem (Helmholtz).
Practice: Assumption is simpler in MEG than in EEG.
Spike Orientation
Theory: Both EEG and MEG can be used to define
orientation of tangential current (= sulcal activity).
Practice: MEG is more useful, neglecting radial current.