module6.6 Flashcards
d circumferential, triangular, bipolar
Circumferential- also called hatband, a montage that goes all around the head in a circle. Most EEG computers have 25 to 32 or more channels. It only takes 10 channels to go around the head so,most circumferential montages fill up the last 15 or so channels with either longitudinal or
transverse rows.
Triangular- an out dated undesirable montage that has a 3 pointed look to it.
Bipolar- a montage that uses 2 (bi) scalp (active) electrodes in each channel, such as Fp1 to F7.
Both Fp1 and F7 are recording from the brain, so they are “active”. This type of montage can also be referred to as sequential, because the electrodes “line up” in sequence. The amplitude of EEG
activity is smaller in bipolar montages because we are subtracting the difference between the 2 electrodes. Focal abnormal activity is localized by phase reversals in a bipolar montage.
define montage, longitudinal, transverse
Montage- a system of labeling EEGs. It is a way of putting the channels in a logical organized
sequence in order to make interpretation easier
Longitudinal- a montage that goes from front to back (anterior to posterior, Fp1 to O1)
Triangular- an out dated undesirable montage that has a 3 pointed look to it
d monopolar, reference, input/grid 1 and 2, derivation,
Monopolar- a montage that uses 1 (mono) scalp (active) electrode referred to an inactive electrode.
Example: input one is Fp1 and input two is A1. Fp1 is recording from the brain, so it is “active”.
A1 is on the cartilage of the ear lobe, where no brain activity is taking place. Therefore, A1 is an
inactive electrode. The amplitude of EEG activity is bigger in monopolar montages because we are
recording the actual voltage of the active electrode instead of the difference between two active
electrodes. (We are subtracting but, the voltage of Fp1 is say 50uV minus the voltage of A1 which
is zero = 50uV.) Monopolar and reference montages are best for displaying low amplitude activity
such as small sharp spikes (14 & 6Hz). Focal abnormal activity is localized by the
electrode/channel with the highest amplitude in a monopolar montage
Input 1 & 2 (Grid 1 & Grid 2)- Every one channel of the EEG machine has two inputs (input 1
and input 2). For example, input 1 of channel 1 could be Fp1 and input 2 of channel 1 could be F7.
Each channel of the EEG machine records the difference between the two inputs.
Derivation: where is coming for
d homologous, open ended derivation, end of chain,
Homologous- the same site in the opposite hemisphere. F7 would be homologous to F8. Your right pinky would be homologous to your left pinky. During the entire EEG, you should be comparing the homologous sites with each other. If channel 1 was Fp1 to F7, you would look for
another channel that had Fp2 to F8 in it.
Open ended derivations- a channel of EEG electrodes that does not have a homologous channel.
For example, if channel 1 was Fp1 to Fp2, there would be no other homologous channel to compare
channel 1 with.
End of chain derivations- montages have “chains” of electrode pairs all in a row. For example, you could have a chain of 4 channels that go from front to back (longitudinal). Channel 1 could be Fp1 to F7, channel 2 F7 to T3, channel 3 T3 to T5 and channel 4 could be T5 to O1. There are two “ends” at both the top and the bottom. The top end is Fp1. There is no other electrode above Fp1,
so it is the end of the chain. The bottom end is O1. There is no other electrode below O1, so it is also the end of a chain
d laplacian, dipole, and horizontal dipole,
used to enhance focal activity by attenuating
generalized activity. An electrode in the area of concern (say C3) is connected to input 1 then four electrodes around it (F3, T3, P3 & Cz) are connected to input 2. In the next channel, you could focus on another electrode (say P3) and connect those accordingly all down the page. A problem
will occur at the end of a chain, for example, if input 1 is O1, what will you put in input 2?
Laplacian montages are easier to use today with digital technology
Dipole- (di means two) dipoles are two equal and opposite charges separated by a short space.
They are electrical sources or generators that project positive and negative electrical fields
horizontal dipoles (also
called parallel generators), which are almost parallel with the surface of the brain, so, both ends of
the dipole can be recorded by scalp electrodes. Two disorders that can create horizontal dipoles are
small sharp spikes (or benign epileptiform transients of sleep (BETS) and Benign Rolandic Epilepsy
(or Benign Epileptiform Central Temporal Spikes BECTS).
define and discuss advantages and disadvantages of each reference electrode (A1/A2, Cz, nose, chin, neck and average reference),
A1 and A2 sometimes have EKG, tension or jaw movement artifacts in them. If every
channel were referred to them, every channel would have artifact in them. There could also be an
abnormality in T3 or T4 that is “picked up” in A1 or A2. Both of these problems are known as a
contaminated reference
