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Electrodiagnostics > EEG > Flashcards

EEG Flashcards

1
Q

EEG

Which neurons are the mains contributors to scalp-recorded EEG signals

A

Pyramidal cells

Arranged in the perpendicular orientation to the cortical surface

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2
Q

EEG

What is the phase convention of EEG waveforms?

A

Downward = +
Upward = -

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3
Q

EEG

What are the two possible EEG montages

A

Referential and bipolar

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4
Q

EEG

How is localisation of a discharge made using a :
a) bipolar montage
b) referential montage

A

a) analysing orientation and amplitude
b) analysing amplitude alone

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5
Q

EEG

What is a bipolar montage

A

Each electrode’s voltage is linked and compared to an adjacent one to form a chain of electrodes. In each chain, an electrode’s voltage is compared to that of the electrode behind it, so each tracing line is a pair of electrodes in which the voltage of the second electrode is subtracted from the voltage of the first. Because of this, in bipolar if the first electrode in the tracing line is more positive/higher than the second, you get a positive, downward deflection; if the second electrode is more positive/higher, you get a negative, upward deflection.

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6
Q

EEG

How to interprete phase reversal in a bipolar montage?

A

With phase reversals, the middle electrode of the pair that makes the reversal is the electrode of maximal voltage (ex. T3-T5 and T5-O1 phase reversal means T5 has the greatest voltage of them all).

Negative discharges cause the surrounding tracings to point toward the electrode of maximal voltage, while positive discharges cause surrounding tracings to point away from the electrode of max voltage (an easy way to remember this: positives can fit a plus sign, and negatives can only fit a negative sign)

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7
Q

EEG

In a bipolar montage, what is an end of chain phenomenon?

A

Occurs when potentials appear with greatest voltage in the last electrode in the chain of electrodes producing waveform deflections that are all in the same direction (no phase reversal). Solution: use another type of bipolar montage (e.g. circumferential montage).

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8
Q

EEG

What is the most common used bipolar montage:

A

Double banana, marked by the bilateral temporal chains over the bilateral parasagittal chains, and a central chain below that.

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9
Q

EEG

What is a referential montage

A

Compare all the electrodes to single reference point.

There are no phase reversals, and as such, the highest amplitude waveform is the one with the greatest voltage, be it downward or upward.

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10
Q

EEG

What is a major limitation to the reference montage?

A

When the active electrode is the reference electrode, all the traces will be deflected in the same direction (following the reference signal). Creates a reference electrode artifact.

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11
Q

EEG

Define low f (high pass) filter

A

filter out frequencies below a certain threshold

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12
Q

EEG

Define high frequency (low pass) filter

A

Filter out frequencies above a certain threshold

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13
Q

EEG

Define notch filter

A

selectively removes 60 Hz activity that arises from electrical interference such as wires and equipment

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14
Q

EEG

Define sensitivity

A

Affects the height of the waveforms.
Higher Se = Lower number = smaller waveforms

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15
Q

EEG

Define page speed or epoch

A

Determines how many seconds of the study are displayed across your computer monitor at one time. Higher speed makes tracing look more stretched, low speed makes tracing look more condensed

note: each division on the epoch represents 1 second

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16
Q

EEG

Name the 4 frequency bandwiths

from low frequency/high amplitude –> high frequency/low amplitude

A
  • Delta (<4 Hz) - deep sleep
  • Theta (4-8 Hz) - sleep
  • Alpha (8-13 Hz) - Awake
  • Beta (13-30 Hz) - Stimulated / mental activity
  • Gamma, low (30-60 Hz)
  • Gamma, high (>70 Hz)
  • Ripples (> 100 Hz) - epileptiform discharges
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17
Q

EEG

Name the patient-origin, physiological artifacts

A

Scalp muscles (EMG)
Eye movements (EOG) - blink (up/down), REM (lateral)
Cardiac muscles (ECG)
Breathing
Blinking
Tongue and jaw mts (e.g. chewing)

https://www.learningeeg.com/artifacts

18
Q

EEG

Name the external, non physiological artifacts

A

Intstrumental
Electrode
Environmental
Digital

19
Q

EEG

Describe the Blink artifact. what is the underlying phenomenon?

A

Large positive (downward) deflection as the eye move upward in its orbit. Only seen in the frontal leads (F3 or F7).

Is a key component of normal, awake EEG.

It is caused by the Bell’s Phenomenon. The eyes’ cornea is positively charged and retina is negatively charged; when you blink, the eyes roll up slightly, and the cornea moves closer to the frontal electrodes Fp1 and Fp2, which thus see a positive signal that is reflected on EEG.

http://www.eegpedia.org/index.php?title=Eye_blink_artifact

20
Q

EEG

Describe lateral eye movements (e.g. REM sleep)

A

Positive frontal deflection on the side to which you look, and a contralateral negative frontal deflection (opposite waveforms in bilateral frontal regions)

21
Q

EEG

Describre muscle artifacts

A

High frequency (40-70Hz), low amplitude. Often dominant in the frontal and lateral tempora leads.

‍‍

22
Q

Describre chewing artifacts

A

Diffuse bursts of fast myogenic artifact; hypoglossal artifact is diffuse and slow, synchronized activity

23
Q

EEG

Describe ECG artifacts

A

Look like negative spikes time-locked to the QRS complex

24
Q

EEG

Describe an electrode pop

A

Single electrode showing a very sudden, steep upslope with a slower downslope and absolutely no field.

25
Q

EEG

Decribe a chewing artifact

A

Muscle artifact from the temporalis muscle. Marked by sudden onset, intermittent bursts of generalized very fast activity.

26
Q

EEG

Describe a hypoglossal artifact

A

It arises from the movement of the tongue, and appears as slower, diffuse delta frequency activity.

27
Q

EEG

Know how to recognize different states of arousal

A
  • Awake: BETA (13-25 Hz). High f, low A. Blink + muscle artifacts.
  • Relaxed: ALPHA (8-12 Hz). Eyes closed.
  • Stage 1: THETA (4-7 Hz). Vertex waves.
  • Stage 2: K-complexes + sleep spindles
  • Stage 3-4: DELTA (1-3 Hz). Low f, high A.
  • REM: Similar to awake but no muscle artifact (atonia). Eye artifacts may be present.

https://www.macmillanhighered.com/BrainHoney/Resource/22292/digital_firs

28
Q

EEG

What is a sleep spindle

A

Burst of bursts of 11–15 Hz activity, typically between 0.5 and 2 s in duration. Often associated with K-complexes.

Feature of stage 2 nREM sleep

29
Q

EEG

What is a k-complex

A

Max at the vertex (Cz) or Fz
Diphasic
Duringe nREM stage 2
Often associated with sleep spindles

https://eegatlas-online.com/index.php/en/alphabetical-index/k-complex-gu

30
Q

EEG

what is a vertex sharp wave

A

Max at the vertex (Cz)
Diphasic
Found in nREM stage 1 +/- 2
smaller amplitude and narrower than K compexes

http://www.eegpedia.org/index.php?title=Vertex_waves

31
Q

EEG

Asymmetric (focal) decreased amplitude may indicate..

A

Focal structural cortical lesion (infarct, hematoma, tumor)

32
Q

Generalized decreased amplitude may indicate

A

widespread cortical dysfunction (post-ictal, hypothermia, subdural hematoma, post-anoxic..)

33
Q

EEG

SEE EEG ABNORMAL

A
34
Q

EEG

Criteria for epileptiform discharges

A
  • High amplitude
  • Polyphasic
  • Different from background
  • Predominantly negative polarity
  • Multiple electrodes involved
35
Q

EEG

Spike

A

Negative, 20-70 ms

36
Q

EEG

Sharp wave

A

Negative, 70-200 ms (wider than spikes)

37
Q

EEG

Spike and slow-wave (SWC)

A

Negative spike followed by 200 ms negative wave

38
Q

Name and recognized 4 ictal activity waveforms

A

Spike-wave (3-5 Hz)
Polyspike-wave
Polyspike (16 Hz)
Polysharp (12 Hz, wider)

39
Q

Ictal vs interictal

A

Ictal: > 3s and/or associated with clinical manifestations (e.g. myoclonus)
Inter-ictal: < 3s except if associated with clinical manifestations

40
Q

Burst suppression

A

Found in GA or coma
if suppression is getting longer = neg Px factor for recovery from coma

READ MORE

41
Q

Electrodecrement

A

Electrodiagnostics (10 decks)

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