EEG Hardware Flashcards
Nasion
depression at the bridge of the nose
inion
The bony prominence at the back of the skull
Preauricular points
slight depressions located in front of the ears and in front of the ears and above the earlobe
Tragus
The flap at the opening of the ear
Vertex (Cz)
The intersection of imaginary lines drawn from the nasion to the inion and between the two preauricular points.
Electrodes included in the 10-20 system and how they are indicated.
They assign electrodes a letter and a subscript. The letters represent the underlying region and include: Fp(frontopolar or prefrontal), F (frontal), C (Central), P (parietal), O (Occipital), and A (Auricular). While a subscript z represents a midline placement. The electrodes on the left side are assigned odd numbers and the electrodes on the right side are assigned even numbers. Numerical subscripts range from 1-8 and increase with distance from the midline.
Subscript z in 10-20 System
midline (central axis from nasion to inion) placement.
In 10-20 system of EEG where are reference electrodes placed?
2 reference electrodes are usually placed on the earlobe or on the mastoid process behind the ears.
Fp stands for what?
Prefrontal or frontopolar
The 10-20 System calculates what?
The distance from the naison to the inion and from the left preauricular notch to the right preauricular notch. The 19 active elctrodes taking either 10% or 20% of these distances.
The American Clinical Neurophysiology society published guidelines for expanding the 10-20 system to 75 electrode sites. This expansion allows what?
It allows clinicians to define the sites midway between the 10-20 sites commonly used in clinical practice, beter localize epileptiform activity, increase EEG spatial resolution, and improve detection of localized evoked potentials.
The modified 10-20 system, with 75 electrodes, called the 10-10 system replaces what sites and with what?
The 10-10 system replaces inconsistent designations (T3/T4 and T5/T6) with consistent ones (T7/T8 and P7/P8).
In the 10-10 system electrodes are located where?
Every 10% along medial-lateral contours and adds new contours. Each electrode site is an intersection betwen a medial-to-lateral coronal line (designated by letters) and longitudinal sagittal line (designated by numerical subscripts).
Electrode labeling in the 10-10 system.
N (naison), Fp (frontopolar, prefrontal), AF (anterior frontal), F (frontal), FT (frontotemporal), FC (frontocentral), A (auricular), T (temporal), C (central), TP (temporal-posterior temporal), CP (centroparietal), P (parietal), PO (Posterior temporo-occipital or parieto occipital), O (occipital), and I (Inion). A subscript z represents a midline (central axis from nasion to inion). Numerical subscripts range 1-10 and increase with distance from the midline. With odd numbers assigned to the left and even numbers to the right
In 10-10 system FC (frontocentral) and FT (frontotemporal) are located where?
along the second intermediate coronal line.
In 10-10 system the location of the Temporal-posterior temporal, and centroparietal.
lie along the third intermidate coronal line.
In the 10-10 system the location of the Posterior temporo-occipital or parieto-occipital
Lies along the fourth intermidate coronal line.
In 10-20 system list electrodes placed from the Nasion to Inion- anterior to posterior and where you would mark to place each.
1) Measure from Nasion to inion. Note the total and keep the tape measure on this line
2) Mark 50% of halfway (this is Cz)
3) Measure 10% from Nasion this is FPz. 20% posterior to FPz is Fz. Fz is 20% anterior to Cz
4) Measure 10% up from Inion this is Oz. 20% anterior to Oz is Pz. Pz is 20% posterior to Cz.
*FPz and Oz are landmarks not a site for electrode placement for EEG measurements but a ground electrode could be placed here.
In 10-20 system what are the electrodes placed along the Ear to Ear (or Pre-Auricular line)? Where are they located along this line?
1) Measure from pre-auricular notch to pre-auricular notch. Find the tragus (the flap opening of the ear). Move forward to the indention between the skull and the jaw. Place the end of the tape measure at this notch, pass it over Cz and to the pre-auricular notch on the oppostie ear. Record this measurement.
2) Mark 50% (or halfway). This should intersect with Cz and form a “+”
3) From Cz, mark on each side towards the tragus. This will be C3 and C4.
4) From C3 and C4 mark 20% towards the tragus. This will be T3 and T4. These sites will be 10% up from the pre-auricular notch, directly above the ear.
In 10-20 system what electrode placements are involved in the circumferential? Where are the location of these electrode placements?
1) Place the tape measure of FPz, T3, Oz, T4, and back to FPz. Record the total circumference.
2) From FPz, mark 5% on either side. This is FP1 and FP2.
3) From Oz, mark 5% on either side. This is O1 and O2.
4) Mark at 10% increments from FP1 and FP2. HTis will be F7 and F8.
5) Mark at 10% increments from O1 and O2. This will be T5 and T6.
what electrode placements are involved in the “final measurements”? Where are these located?
1) Measure from Fz to F7: 50% between these points is F3
2) Measure from Fz to F8: 50% between these points is F4
3) Measure from Pz to T5: between these points is P3.
4) Measure from Pz to T6: 50% between these points is P4.
The Steps for site preperation for EEG
1) Identify and mark the spot where electrode will be placed.
2) Prepare the scalp before applying the electrodes. Slightly abrade the skin to remove dead skin, dirt, and oil that can weaken the EEG signal.
3) Scoop a small quantity of NuPrep skin preperation gel on a cotton swab or tissue
4) With the thumb or index finger of one hand, seperate the hair around the electrode site that was previously found and marked
5) Run the gel in the direction of the natural line formed along the scalp by spliting the hair. Some light force must be used, enought to redden the scalp slightly, but not enough to break the skin.
6) Wipe away the excess prepping gel with a dry, lint-free cloth. Take care to keep hair parted and to keep track of the site after wiping clean.
7) A small amount of Ten20 conductive paste should be smeared on the newly prepared site. This keeps track of the site, moves the hair neatly out of the way, and acts as a landing pad for the electrode once it is ready to apply.
8) Start by securing the electrode cables to the patient. Loop the three electrode cables around the plastic clip provided with the EEG-Z sensor. Attach the clip to the back of the shirt collar (90 degree angle for best placement). Keep the heavy DIN cable and EEG-Z sensor underneath the clip, and the light electrode cables above it.
9) Fill the electrode cup with Ten20 conductive paste so no air bubbles exist in the cup.
10) Add more conductive Paste onto the cup electrode, just enough to form a ball on the cup, not so much that it spills over the edge.
11) Place the cup face down on the landing pad previously prepared. Gently push the electrode down to fix it to the scalp. A little bit of paste should run out along the edge of the cup to form a thin ring around it. Place the electrode so that the direction of the cables does not place undue stress on the cup (so it gets pulled off, lifted or twisted off). The cable should hang naturally and towards the plastic clip. Leave enough slack in the cable to allw for comfotable head movement.
12) Repeat the above preperation and placement steps on the earlobes. Do not put too much paste on the ear clip electrode, but ensure the gold clip is completely covered.
13) Leave enough slack on the cables to allow patients to easily turn their head but not to easily that the cables get caught.
What type of electrodes are recommended?
Silver-silver chloride and gold disk electrodes because of low electrode noise. Silver-silver chloride electrodes increase stability in recording very slow EEG frequencies.
Why is it important for the electrodes used to be identical?
It minimizes artifact by imbalanced impedance.
When should glue be used to secure electrodes and when is paste acceptable to be used?
Glue should be used for recordings longer than 30 minutes. Paste are acceptable when recordings are shorter than 30 minutes orinvolve young infants in isolettes (incubator).
What does each color in cable stand for?
- Blue is always positive and an active electrode
- Yellow is negative and the reference in monopolar recordings but in bipolar readings it is an active.
- Black is ground.
Monoploar method of EEG recording
Uses one active and one ground electrode
- The active electrode is placed over a site that is a known EEG generator like Cz.
- The ground electrode is placed over sites like the earlobes that are not known EEG sources and less electrically active. The ground can actually be a combination of two earlobe electrodes. Both earlobes can be electrically or virtually (in software) connected to produce a linked-ears reference.
Bipolar method of EEG recording
Uses an active electrode and a reference electrode to detect differences in electrical potential, and both electrodes are in known active fields.
Where can a reference electrode be placed In EEG recordings
- In a monopolar recording the reference will be located on a site that in not an EEG source like the earlobe
- In an active recording the reference is placed where there is an EEg source * A reference on the earlobe and mastoid preserve phase-synchronous signals (EEG signals whose peaks and valleys coincide).
EEG signal is equal to
Active - reference
A derivative
is a combonation of electrodes used in a single amplifier channel.
A montage is
one or several derivatives chosen to detect loacalized or global EEG activity.
montage reformatting
permits data analysis where an electrode site can be referenced to other sites or combinations of sites.
Monopolar motage or referential montage
Uses earlobe or mastoid process references.
A bipolar or sequential montage does what
compares 2 adjacent electrodes at 10-20 system coordinates inserted into physical or virtual inputs 1 and 2.
What is the difference between a yellow, blue and black electrode
Nothing they are exactly the same it is their placement that matters. The colors code for where they should be placed.
Advantages and disadvantages of a bipolar or sequential montage
- Allows good detection of localized EEG activity, but poor detection of widely distributed EEG activity, since it subtracts synchronous EEG activity. Analysis of asymmetry is only adequate.
- Permits excellent detection of electrode artifact
Frequency of delta wave
below 4 Hz
Frequency of Theta
4-7 Hz
Frequency of Alpha
8-12 Hz
Frequency of SMR
12-15 HZ
Frequency of Beta
13-21
Frequency of high beta
16-20 HZ
