Transcript agenda.ct.infn.it

GridEEG – User training
EEG data preparation
EEG signal quality check
EEG methods
Outcome evaluation
EEG data preparation
Experimental conditions
Subjects sit in a comfortable chair,
in a dimly-lit room.
Awakening resting state eyesclosed.
EEG recording parameters
EEG data must be acquired through
a standard 10-20 International
System consisting of 19 electrodes.
Reference: average signal of the
earlobes electrodes A1, A2.
EEG sampling frequency: 128 Hz
EEG pass-band: 0.3-40 Hz
EEG data preparation
Data format
Dataset composition
The dataset consists of at least 50
artifact-free EEG segments of 2 seconds,
not necessarily contiguous. Each segment
must be stored in a separate ASCII file.
Different .txt files must be numbered
progressively, i.e. Patient_1.txt,
Patient_2.txt, …, Patient_50.txt
F3 F4 ... ... ... ... ... O2
1
2
.
Time samples
EEG data must be organized according to
the standard Neuroscan ASCII format, i.e.
a .txt file of numbers where columns
indicate electrodes and rows indicate
consecutive time samples.
The order of the electrodes in the ASCII
file must be the F3, F4, T3, T4, C3, C4, P3,
P4, FZ, CZ, PZ, Fp1, Fp2, F7, F8, T5, T6,
O1, O2
Electrodes
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.
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N
0.3 0.2 ... ... ... ... ... ... 0.7
0.1 0.4 ... ... ... ... ... ... 0.6
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
... ... ... ... ... ... ... ... ... ...
0.5 0.1 ... ... ... ... ... ... 0.8
Patient_1.txt
EEG signal quality check
Although EEG is designed to record cerebral activity, it also
records electrical activities arising from sites other than the
brain. The recorded activity that is not of cerebral origin is
termed artifact.
EEG segments contaminated by artifacts should be
removed from the subsequent analysis.
Artifacts can be divided into physiologic and extraphysiologic:
Physiologic artifacts are generated from the patient, they arise
from sources other than the brain (ie, body)
Extraphysiologic artifacts arise from outside the body (ie,
equipment, environment).
EEG signal quality check
F3
F4
T3
T4
C3
C4
P3
P4
FZ
CZ
PZ
Fp1
Fp2
F7
F8
T5
T6
O1
O2
Physiologic: Muscle activity
Myogenic potentials are the most common artifacts (see images below). Frontalis and temporalis muscles (eg,
clenching of jaw muscles) are common causes. Generally, the potentials generated in the muscles are of shorter
duration than those generated in the brain and are identified easily on the basis of duration, morphology, and
rate of firing.
EEG signal quality check
F7
F7
Fp1
T3
T4
Fp1
T3
T4
F8
F8
C4
P3
P4
FZ
Fp2
PZ
Cz
F4
F3
F8
T5
T6
O1
O2
C4
P3
P4
FZ
Fp2
PZ
Cz
F4
F3
F8
T5
T6
O1
O2
Physiologic: Eyes movements
Vertical eye movements typically are observed with blinks. A blink causes the positive pole (ie, cornea) to move
closer to frontopolar (Fp1-Fp2) electrodes, producing symmetric downward deflections. Lateral eye movements
most affect lateral frontal electrodes F7 and F8.
EEG signal quality check
F3
F4
T3
T4
C3
C4
P3
P4
FZ
CZ
PZ
Fp1
Fp2
F7
F8
T5
T6
O1
O2
ECG
Physiologic: Electrocardiogram artifact
Some individual variations in the amount and persistence of ECG artifact are related to the field of the heart
potentials over the surface of the scalp. ECG artifact is recognized easily by its regularity and coincidence with the
ECG tracing.
EEG signal quality check
F3
F4
T3
T4
C3
C4
P3
P4
FZ
CZ
PZ
Fp1
Fp2
F7
F8
T5
T6
O1
O2
Physiologic: Skin artifact
Biological processes and/or defects may alter impedance and cause artifacts. Sweat is a common cause. Sodium
chloride and lactic acid from sweating reacting with metals of the electrodes may produce huge slow baseline
sways.
EEG signal quality check
F3
F4
T3
T4
C3
C4
P3
P4
FZ
CZ
PZ
Fp1
Fp2
F7
F8
T5
T6
O1
O2
Extra-physiologic: Electrode impedance
The most common electrode artifact is the electrode popping. Morphologically this appears as single or multiple
sharp waveforms due to abrupt impedance change. It is identified easily by its characteristic appearance (ie,
abrupt vertical transient that does not modify the background activity) and its usual distribution, which is limited
to a single electrode.
EEG signal quality check
F3
F4
T3
T4
C3
C4
P3
P4
FZ
CZ
PZ
Fp1
Fp2
F7
F8
T5
T6
O1
O2
Extra-physiologic: Alternating current (50-60 Hz)
Adequate grounding on the patient has almost eliminated this type of artifact from power lines. The problem
arises when the impedance of one of the active electrodes becomes significantly large between the electrodes and
the ground of the amplifier. In this situation, the ground becomes an active electrode that, depending on its
location, produces the 50/60-Hz artifact.
EEG Methods
Power Spectral Density of cortical regions
Linear Inverse Problem
b
x
Scalp electrodes
Cortical sources
A
Lead field matrix
MRI images
Power of the cortical oscilations at
different frequency bands
EEG Methods
Spectral coherence between scalp electrodes
Elec. (i)
Cij ( f ) 
Elec. (j)
ordinary coherence
Network extraction at
specific frequency
partial coherence
M ij ( f )
M ii ( f )M jj ( f )
Mij = cross-spectrum minor
Mii, Mjj = auto-spectra minors
EEG Methods
Directed Transfer Function between scalp electrodes
Elec. (i)
Elec. (j)
H = inverse of the multivariate
autoregressive matrix
Network extraction at
specific frequency
EEG Methods
Classification through Mahalanobis distance
Nold
Healthy population
Actual subject (X)
Dm ( x)  ( x   )T S 1( x   )
X = EEG features of actual subject
u = population mean EEG features
S = Covariance matrix
Alzheimer population
Dm (x, AD)
AD
Dm (x, Nold)
Data analysis through WEB portal
GridEEG
Physician
Scientist
Default parameters
Customizable parameters
Frequency ranges
Delta (2-4 Hz), Theta (4.5-8 Hz), Alpha1 (8.5-10.5 Hz), Alpha2 (11-13 Hz),
Beta1 (13.5-20 Hz), Beta2 (20.5-30 Hz), Gamma (30.5-40 Hz)
EEG features
PSD (Occipital, Alpha1), ( Occipital, Delta), (Parietal, Alpha1)
COH (P3,C3, Alpha1), (T3,F3, Alpha2), (Pz,Fz, Alpha2)
DTF (O2,P4, Alpha1), ( Cz,Pz, Beta2), (Pz,Fz, Alpha2)
Demonstration and practice:
GridEEG in action
https://applications.eu-decide.eu//grideeg