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Transcript of Simultaneous EEG and f MRI Acquisition
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Simultaneous EEG and fMRI Acquisition
Simultaneous EEG and fMRI Acquisition
Mark CohenUCLA Brain Mapping
Center
Mark CohenUCLA Brain Mapping
Center
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
OutlineOutline
• Motivation: It’s hard, why bother?• Problems and Solutions• Early Results
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
QuickTime™ and aTIFF (Uncompressed) decompressor
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Levels of UnderstandingLevels of Understanding
fMRI-EEG
Fiber Tracingregional connectivityFiber Tracingregional connectivity
fMRIfunctional nuclei or processing centersfMRIfunctional nuclei or processing centers
EEG & Autoradiographycell assembliesEEG & Autoradiographycell assemblies
Multi-unit Recordinglocal circuits: columns, retina…
Multi-unit Recordinglocal circuits: columns, retina…
Single Unit Electrophysiologyaction potentials, chemomodulation
Single Unit Electrophysiologyaction potentials, chemomodulationCrystallography, Chromatography (etc…)
transmitters, ion channels, membrane proteinsCrystallography, Chromatography (etc…)
transmitters, ion channels, membrane proteins
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Presumed Origin of the EEGPresumed Origin of the EEG-- -- -- --
++++
++++ ++
++
Skin
Bone
CSF
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Many Neurons are Not “Seen” by EEGMany Neurons are Not “Seen” by EEG
Bone
Skin
Bone
CSF
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
General Limitations in EEG LocalizationGeneral Limitations in EEG Localization
• Deeper Sources Show Weaker Signals• Magnitude Depends on Dipole Orientation• Magnitude Depends on Temporal
Synchrony• Magnitude Depends on Spatial Coherence• Conductivity of Body Tissues (CSF, scalp)
Blur the Scalp Potentials
• Deeper Sources Show Weaker Signals• Magnitude Depends on Dipole Orientation• Magnitude Depends on Temporal
Synchrony• Magnitude Depends on Spatial Coherence• Conductivity of Body Tissues (CSF, scalp)
Blur the Scalp Potentials
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Source LocalizationEEG Source Localization
1) High resolution raw dataa) High temporal resolution EEGb) High spatial resolution imaging
2) Computational Capacity3) Accurate Mathematical Models
a) Maxwell’s Equation forward model
b) Non-singular Inversion4) Accurate Physiological Parameters
a) Conductivity of all relevant tissues
1) High resolution raw dataa) High temporal resolution EEGb) High spatial resolution imaging
2) Computational Capacity3) Accurate Mathematical Models
a) Maxwell’s Equation forward model
b) Non-singular Inversion4) Accurate Physiological Parameters
a) Conductivity of all relevant tissues
≥10 kHz≤ 1 mm
QuickTime™ and aTIFF (Uncompressed) decompressor
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after Massoud Akhtari
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Source LocalizationEEG Source Localizationafter Massoud Akhtari
?
?
?
??
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
The Scalp Waveform is DistortedThe Scalp Waveform is Distorted
MEG ECoG
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
the Brain and Skull Exhibit Complex Impedancethe Brain and Skull Exhibit Complex Impedance
100 1000 Hz10
100 1000 Hz10
Con
duct
ivity
,
phas
e
The observed spectrally-dependent conductivity implies not only Resistive elements, but both Capacitive and Inductive energy storage.
R
R
L
C
Akhtari, unpublished
Such elements result in substantial phase lags that can alter the dipole localization by several millimeters.
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
How does BOLD relate to neural firing?How does BOLD relate to neural firing?
Energy Demands in TransmissionPre-synaptic:
Transmitter SynthesisExocytosisTransmitter re-uptake
Post-SynapticMaintenance of membrane potential after ion leakageExcitatory: Removal of Sodium (Na/K pump)Inhibitory: ???
Energy Demands in TransmissionPre-synaptic:
Transmitter SynthesisExocytosisTransmitter re-uptake
Post-SynapticMaintenance of membrane potential after ion leakageExcitatory: Removal of Sodium (Na/K pump)Inhibitory: ???
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Red and Green SpikesRed and Green Spikes
EEG-correlated fMRI, New York
Seizure Activity Spreads from an Irritative Zone
Seizure Activity Spreads from an Irritative ZoneHypotheses:
•Initial Event is Energetically Costly
•Spreading Depolarization is Not
Hypotheses:
•Initial Event is Energetically Costly
•Spreading Depolarization is Not
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Spike-triggered ImagingSpike-triggered Imaging
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Spike-Triggered fMRISpike-Triggered fMRI
• Complex partial seizures, rare generalization
• EEG: generalized interictal discharges, some with left temporal onset
• MRI: normal
• Complex partial seizures, rare generalization
• EEG: generalized interictal discharges, some with left temporal onset
• MRI: normal
• Complex partial seizures, occasional generalization
• EEG: multifocal and generalized interictal discharges
• MRI: symmetric subependymal heterotopias
• Complex partial seizures, occasional generalization
• EEG: multifocal and generalized interictal discharges
• MRI: symmetric subependymal heterotopias
Warach, et al. (1996)
RR RR
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Project GoalsProject Goals
• Unaltered MR Image Quality• Diagnostic Quality EEG During functional
MRI:Artifact FreeDense Array of Channels
• Tomographic Correlation of Scalp Electrical Activity
• Amplifiers Suitable for Single Units• Subject Safety
• Unaltered MR Image Quality• Diagnostic Quality EEG During functional
MRI:Artifact FreeDense Array of Channels
• Tomographic Correlation of Scalp Electrical Activity
• Amplifiers Suitable for Single Units• Subject Safety
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Artifacts - MRIArtifacts - MRI
RF Noise
Magnetic Field DistortionNon-magnetic material such as Silver
• Properly-shielded Amplifiers
• Softened Logic Pulses
• Careful Lead Dress
• Eliminate RF Loops
Signal Losses
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Inductive Pickup by EEG leadsInductive Pickup by EEG leads
BallistocardiogramBallistocardiogram
Imaging Field GradientsImaging Field Gradients
++
––
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Ballistocardiogram SubtractionBallistocardiogram Subtraction
0 1 2 3time (sec)
QRS
EKG
A
B
A-B
Goldman, et al., Clinical Goldman, et al., Clinical Neurophysiology, 2000Neurophysiology, 2000
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
ECG correctionECG correction
•Fourier detection of nominal heart rate
•Bootstrap detection of QRS based on template
•Adaptively create template of complete ECG
•Outlier and error monitoring
•Further detection based on statistical correlation peak
•Continuous adaptation of nominal HR and waveforms
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Approach to MR Artifact RemovalApproach to MR Artifact Removal
EEGEEGkk
SSkk=EEG=EEGkk++ArtifactArtifact
ArtifactArtifact
• EEGEEGkk and and ArtifactArtifact are are uncorrelateduncorrelated
• EEGEEGkk and and ArtifactArtifact add add linearlylinearly
• ArtifactArtifact is identical at each is identical at each time (time (kk))
This approach requires that:
kk=1=1
NN
SSkk
NN
–
+
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Lead ConfigurationEEG Lead Configuration
Minimized Current Induction:• High Impedance Carbon Fiber Leads• Reduced loop area• Self canceling currents
Minimized Current Induction:• High Impedance Carbon Fiber Leads• Reduced loop area• Self canceling currents
Hard-Wired Bipolar Montage:• Dual lead electrodes• Twisted lead pairs• Local differential amplifiers
Hard-Wired Bipolar Montage:• Dual lead electrodes• Twisted lead pairs• Local differential amplifiers
A B C
+ + ––
Goldman, et al., Clinical Neurophysiology, 2000
Patent Applied For
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Physical ApparatusEEG Physical Apparatus
Goldman, et al., Clinical Goldman, et al., Clinical Neurophysiology, 2000Neurophysiology, 2000Patent Applied For
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Twisted Lead Noise ReductionTwisted Lead Noise Reduction
twisted
untwisted
0 1 2time (sec)
fp2f8
c4p4
fp1f7
c3p3
no scan scan
Goldman, et al., Clinical Goldman, et al., Clinical Neurophysiology, 2000Neurophysiology, 2000
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Amplifier RecoveryAmplifier Recovery
1 sec1 sec
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Receiver SaturationReceiver Saturation
++
––
ININ
2 Hz2 Hz
OUT OUT
150 mV150 mV
Time (sec)Time (sec)11 22
OUT OUT
150 mV150 mV
Time (sec)Time (sec)11 22
ININ
DC offsetDC offset
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Functional Block DiagramEEG Functional Block Diagram
TwistedPair
Leads
DifferentialAmp
IsolationBarrier
ShieldDriver
+
–1 358
64
72
Low Pass
73
High Pass
Range detect
+
–
Patent Applied For
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
After DC Offset control & Low Pass FilterAfter DC Offset control & Low Pass Filter
0 0.1 0.2 0.3sec
msec
100 µV
0 5 10 15 20 25
10 µV
Gradient Artifacts are not eliminated completely by analog means.
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Fast Sampling is NOT enoughFast Sampling is NOT enough
Raw SignalRaw Signal
After After Subtraction of Subtraction of Averaged Averaged ArtifactArtifact
After After Subtraction of Subtraction of Averaged Averaged ArtifactArtifact
0 0.1 0.2 0.3 0.4 0.5 0.6
0 5 10 15 20 25 0 5 10 15 20 25
100 µV
10 µV
Sampling rate: 10 kHz
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Residual ErrorsResidual Errors
cos(2ft) cos(2ft )
cos(2ft)cos( 1) sin(2ft)sin
…where:ƒ is the frequency of the artifact is the phase error, equal to 2πf0/fs,
- f0 is the EPI readout frequency and- fs is the sampling frequency.
At high sampling frequency (small At high sampling frequency (small ) the error, ) the error, , is , is linearly proportional to the sampling frequencylinearly proportional to the sampling frequency
tt
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
––++
––++
Triggered Adaptive CorrectionTriggered Adaptive Correction
Trigger once per trTrigger once per tr
EEGEEG
++ ––
Fc=100 HzFc=100 Hz≥≥200 s/s200 s/s16 bits16 bits
AveragingAveraging
++
––
DigitizationDigitizationAnalog FilterAnalog Filter
DifferentialDifferentialAmplificationAmplification DC OffsetDC Offset
CorrectionCorrection
Corrected EEGCorrected EEG
Patent Applied For
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Sampled Gradient Drive CurrentSampled Gradient Drive Current
0 0.5 1 1.5 2 2.5 3Time (seconds)
Uncorrected
Average N=30
Corrected
Corrected X 5
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Correction During Continuous ScanEEG Correction During Continuous Scan
tr = 2.5 ste = 30 ms20X20 cm15 slices
2000 3000 4000 5000 6000 7000Time (msec)
50 µV
Cohen
UCLA BrainMapping CenterColumbia University 5/11/04
MRI-Compatible EEG System DesignMRI-Compatible EEG System Design
Within the MR scanner
64 ChannelLocal Amplifier
Analog to Digital Convertor & Digital Signal Processor
EEG Display
USB over Optical Fiber
EEG Leads
(anonymized subject)(anonymized subject)
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
State MeasurementsState Measurements
EEG may be the best available measure of state:
Sleep Attentiveness Arousal Responsiveness
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
0 1 2 3 4 5 6 7 8 9 10Time (seconds)
EEG during Sleep (corrected)EEG during Sleep (corrected)
fp2-f8
fp8-t4
t4-t6
t6-o2
fp2-f4
c4-p4
p4-o2
f4-c4
fp2-f8
fp8-t4
t4-t6
t6-o2
fp2-f4
c4-p4
p4-o2
f4-c4
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
UCLA: Simultaneous fMRI & Epileptiform EEGUCLA: Simultaneous fMRI & Epileptiform EEG
fp2-f8
f8-t4
t4-t6
t6-o2
fp1-t7
t7-t3
t3-t5
t5-o1
fp2-f4
f4-c4
c4-p4
p4-o2
fp1-f3
f3-c3
c3-p3
p3-O1
1 sec
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Spectral ContentEEG Spectral Content
Goldman, et al., Clinical Goldman, et al., Clinical Neurophysiology, 2000Neurophysiology, 2000
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Linear Systems ApproachLinear Systems Approach• Linear• Time-
Invariant• (LTI) System
x(t)x(t) y(t) = ƒy(t) = ƒ[[x(t)x(t)]]
ƒ(A + B) = ƒ(A) + ƒ(B)ƒ(A + B) = ƒ(A) + ƒ(B)
If h(t) is the response to an impulse:
y(t) h()x(t )d
x(t) * h(t)
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Response Latency vs. Stimulus DurationAverage of 10 recordings
Data courtesy R. Savoy / Mass. General Hospital
1 sec flash
17 ms flash
100 ms flashStimulusOnset
Signal
1840
1860
1880
1900
1920
15 20 25 30 35Time (seconds)
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
•••••••••••••••
••
•
•••••
•
•
•
•••••
-10
0
10
20
30
40
50
0 2 4 6 8 10 12 14 16
Brain Impulse Response
Time (seconds)
MR Signal (a.u.)
Raw Data from R. Savoy
Light Flash
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
0 25 50 75 100 125 150 175 200 225 2500
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
time (sec)time (minutes)
1 2 3 40
Ave
rage
Pow
er (
µV
2 )
Alpha MappingAlpha Mapping
spectral power in the alpha bandpredicted BOLD
response
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Spectral Time CourseSpectral Time Course
8
10
12
14
16
18
20
22
24
26
28
0 50 100 150 200 250
µV
Time (seconds)
Theta Alpha Gamma
5
10
15
20
25
15 20 25Gamma
Theta
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Simultaneous Imaging for Tomographic Electrophysiology
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG spectral fMRIEEG spectral fMRI
+ 0.6
± 0.3
– 0.6
Goldman, et al., NeuroReport, 2003
Patent Applied For
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Q&AQ&A
QQ: Do the spectral bands adequately : Do the spectral bands adequately describe the EEG?describe the EEG?
QQ: Is the forward convolution model : Is the forward convolution model valid?valid?
QQ: What is the explanatory power of : What is the explanatory power of the data?the data?
AA: : Ask a mathematician.Ask a mathematician.
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
NNkk
PARAFACPARAFAC
EEGEEGSSftdftd
kk
aa
bb
cckk
kk
kk
F. Miwakeichi, et al., NeuroImage 22, 2004
frequency
time
channel
S(Nd X Nw X Nt) is a three
dimensional matrix, d are the electrode pairs, w is frequency and t is time.
ˆ S dwt adkbwkc tk dwt
k1
Nk
Each atom, Each atom, kk, is the trilinear combination of , is the trilinear combination of f, tf, t and and dd
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
NNkk
PARAFACPARAFAC
EEGEEGSSftdftd
kk
aa
bb
cckk
kk
kk
AA
BB
CC
F. Miwakeichi, et al., NeuroImage 22, 2004
frequency
time
channel
ˆ S dwt adkbwkc tk dwt
k1
Nk
The “corcondia”The “corcondia” (=core consistency diagnostic)(=core consistency diagnostic) constraint determines N constraint determines Nkk..
A a k , B bk , & C ck Find:Find:
that explain that explain SS with minimal error. with minimal error.
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
the Atomthe Atom
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
PARAFAC applied to SITE dataPARAFAC applied to SITE data0.40.4
0.30.3
0.20.2
0.10.1
1010 2020 3030 4040 50500.10.1
00
Rel.Rel.EnergyEnergy
Frequency (Hz)Frequency (Hz)
thetatheta
alpha gamma
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Trilinear Partial Least SquaresTrilinear Partial Least Squares
kk
Maximize covarianceMaximize covariance
EEGEEGSS ftdftd
kk
aa
bb
cc kk
kk
kk
AA
BB
CCfrequency
time
channel
voxel
time
uu
vvkk
kkUU
VV
fMRIfMRIff stst
E. Martinez-Montes, et al., in preparation, 2003
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Trilinear Partial Least SquaresTrilinear Partial Least Squares
ˆ S dt adkbkctk edkk1
Nk
ˆ F st uskvtk stk1
Nk
Establish a structural model:
EEG
fMRI
then,Maximize the covariance of ck and uk
E. Martinez-Montes, et al., in preparation, 2003
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Correlation of EEG and fMRI dataCorrelation of EEG and fMRI data
Alphar2 = 0.83p < 0.05
Thetar2 = 0.56p ≈ 0.07
Gammar2 = -0.03p = n.s.
E. Martinez-Montes, et al., in preparation, 2003
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
JackKnife pseudo t-imageJackKnife pseudo t-image
E. Martinez-Montes, et al., NeuroImage 22:1023-34, 2004
LL RR
Alpha
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Direct Dipole MappingDirect Dipole Mapping
LORETA solution to alpha atom - Source Spectrum Imaging
E. Martinez-Montes, et al., in preparation, 2003
LL RR
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Apple PowerPCApple PowerPC
Subjectin Magnet
the UCLA Autocerebroscope
the UCLA Autocerebroscope
Statistical Detection of Signal Changes
Time Series of Images
MR ScannerMR Scanner
GE/ANMRGE/ANMR
Radio Signal
SITE E-physSITE E-phys
Stimulus Stimulus PresentationPresentation
Resonance TechnologyResonance Technology
Functional Functional ImageImage
Research supported under DA13054
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Changing the LandscapeChanging the Landscape
Non-Invasive Highly Invasive
3
2
1
0
-1
-2
-3
-4
brain
map
column
layer
neuron
dendrite
synapse
-3 -2 -1 0 1 2 3 4 5 6 7millisecond second minute hour day
Log10 seconds
Log10
millimeters
LesionsPET
2-Deoxyglucose
Microlesions
Light Microscopy
Light MicroscopyPatch ClampPatch Clamp
Optical ImagingOptical Imaging
Single UnitSingle Unit
MEG / ERPMEG / ERP
fMRI
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
Levels of UnderstandingLevels of Understanding
fMRI-EEG
fMRI- EPhys
fMRI-Microdialysis
Ephys-Microdialysis
Cohen
UCLA BrainMapping CenterColumbia University 5/11/04
Richard DuBoisRichard DuBois
Robin GoldmanRobin Goldman
Susan BookheimerSusan Bookheimer
Ahmad HaririAhmad HaririAlison
Burggren-Clements
Alison Burggren-Clements
Meredith BraskieMeredith Braskie
Fred SabbFred Sabb
Zrinka BilusicZrinka Bilusic Alex KorbAlex Korb
Thanks to the GangThanks to the Gang
Jennifer BramenJennifer Bramen
Smoke Imagery Invert EndICAEnergy
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Massoud AkhtariMassoud Akhtari
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
in my dreams…in my dreams…
RF Probe XRF Probe X
RF Probe YRF Probe Y
RF Probe ZRF Probe Z
Electrical ProbesElectrical Probes
Inner CannulaInner CannulaSemi-Semi-permeable permeable MembraneMembrane
Outer CannulaOuter Cannula
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
thanksthanksNIDA DA13054 DA13627
DA15549 DA14093NEI EY12722Epilepsy Foundation of America UCLA Eugene Cota-Robles Fellowship
Amir AbrishamiDeane AikinsPete EngelEduardo Martinez-MontesFumikazu MiwakeichiMark SimonJohn SternNelson TrujilloPedro Valdes-Sosá
John Mazziotta
Robin GoldmanRobin Goldman
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG spectral ƒMRI (2)EEG spectral ƒMRI (2)
alpha (8-12 Hz)
beta (12-30 Hz)
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
EEG Functional Block DiagramEEG Functional Block Diagram
Multi-plexer
OptoIsolator
RFShield
74 78 82Single Board Computer
TwistedPair
Leads
DifferentialAmp
IsolationBarrier
Latch
DAC
ADC
ShieldDriver
+
–
+
–
1 358
6368
70
64
66
72
Low Pass
76
OptoIsolator
TCP/IP TCP/IP
GradientTriggerGradient
Trigger
ECG
Cohen 7/23/04
UCLA BrainMapping CenterIPAM - UCLA
Applications (triggered sampling)Applications (triggered sampling)
• EEG-fMRI.EEG-fMRI.
• Other physiological signals and fMRI Other physiological signals and fMRI (EKG, EMG, etc…)(EKG, EMG, etc…)
• Hum (60 Hz noise) in digital audio and Hum (60 Hz noise) in digital audio and telephony.telephony.
• Carrier Suppression in Radio, Radar Carrier Suppression in Radio, Radar and Television.and Television.
• ……any conditions in which signals are any conditions in which signals are digitized in conditions where digitized in conditions where repeatable noise contaminates the repeatable noise contaminates the signal.signal.