combined EEG instrumentation & artifacts exam short response

Cancellation

Inputs are the same or almost the same resulting outputs to be 0 or minimal

Summation

When inputs are positive or negative or very different

Electrical field

Area of the brain where electrical activity spreads out focal to surrounding areas

Dipole

Equal AND opposite charged poles separated by distance

Attenuation

Smaller in amplitude

Accentuation

Bigger in amplitude

Bandwidth

Number of waves affected by frequency filters

Frequency response curve

Graphic chart used to understand behavior of amplifiers or filters

Time constant

(LFF) Time it takes in seconds for a square wave to decay 37% of its initial amplitude

FP1 (30 uv) - F3 (50 uv)

-20 UV, upward

If input 1 is more positive than input 2, the pen goes___

Downward

Define differential amplification and provide a simple numeric example

A software that amplifies relative voltage differences in an EEG channel

FP1(30 uv) - F3(50uv) = -20 uv

Define CMR and explain why it matters in EEG recording quality

Software that rejects signals in common and it matters because if the electrodes are close to each other, it will show no signals in the tracing.

Describe ‘ end of chain ; effect in bipolar montages and one maneuver to address it

Most anterior to posterior in longitudinal bipolar montages where polarity is revered in the most posterior channel and is common in double banana. When there is an end of chain, you switch it circumferential montage to find a focus.

Describe the double banana (longitudinal bipolar) montage and how a focal abnormality is localized

Electrode channels are linked anterior to posterior and/or left to right chains. Phase reversal is localized in double banana and it is where reversed polarity in adjacent channels is present as a focus. When one channel is negative pen deflection and the other channel pen deflection is positive then the focus is a positive phase reversal.

Describe the transverse (coronal bipolar) montage and when it is commonly used and how it helps identify laterality

In a longitudinal bipolar montages where the electrodes are linked left to right and is used for sleep. It identify sleep architecture like k-complex

Describe the circumferential (hat) montage and one scenario where it is helpful

In a longitudinal bipolar montage where the electrodes are measured around the head and it useful for end of chain to find a focus when there is none in double banana.

Define attenuates vs accentuates (when acted upon by filters/sensitivity)

Attenuates is reduce in amplitude waves, when the sensitivity increases, the waveform attenuates

Accentuates is increase in amplitude, when the sensitivity decreases, the waveform accentuates

Define amplitude and morphology

Amplitude is the height of the wave from peak to crest upon voltage

Morphology is the shape of a wave

Synchronous, asynchronous, and hyper synchronous

Synchronous is the same frequency

Asynchronous is not the same frequency in opposite lateralized chain

Hyper-synchronous is vary in same frequency

Define encephalopathy (EEG context)

Disease of the brain, generalized, diffuse, slowing delta and theta waves

Define A-P gradient

Fast and attenuated frequency in anterior areas of the eeg channel

Gradually slow and accentuated frequency in posterior areas of the EEG channel.

Define PDR

Eyes closed, awake, resting, alpha frequency accentuating (Bell’s phenomenon)

Define average reference montage and a typical pitfall

Averages all the reference electrodes on the scalp and to find focal activity.

A pitfall will be reference electrode contamination which will show artifact.

Define ipsilateral and contralateral

Ipsilateral is in referential montage where the reference electrodes are placed on the same side of the head

Contralateral is in referential montage where the reference electrodes are placed on the opposite side of the head

Define phase reversal

In longitudinal bipolar montage, where reversed polarity is in adjacent channels that is present as a focus.

Define polarity

Positive or negative pen deflections based on relative neuronal discharges in a channel.

Define electrical field

Area of the brain where electrical activity spreads out focal to surrounding areas

Define hemisphere, lateralized, diffuse, generalized, and bilateral

Hemisphere- anterior to posterior or left to right of the brain

Lateralized- seen on one hemisphere/channel

Diffuse - spread throughout the channel

Bilateral- seen on both hemisphere/channel

Generalized- seen in all channels

Define variability, reactivity, and continuity

Variability- variety of frequency and waveforms in a tracing

Reactivity- changes in frequency and amplitudes in response to external stimulus

Continuity - consistent or unbroken wave

Define electrodecrement

Severe attenuation

Name and briefly describe 3 types of phasic waves

Monophasic- crossed the baseline once

Biphasic - crossed the baseline twice

Polyphasic - crossed the baseline multiple times

Name and describe 2 basic morphologies of a wave

Spike - 20-70 ms

Sharp - 70-200 ms

Explain how to localize a focus in a referential montage using amplitude relationships

You localize in a referential montage using amplitude differences in input 1 and input 2 and use average reference to confirm a focus.

Explain how to localize a focus in a bipolar montage using phase reversals

Phase reversal is reversed polarity in adjacent channels present as a focus. If one channel is negative and the other channel is positive pen deflections then the focus is a positive phase reversal.

What can you do if you think your abnormality is end of chain? Give two options

Circumferential hat and Referential to confirm the focus

Describe common environmental noise sources in EEG and a fix for each

IV pumps and feeding pumps

Ask the nurse if they can unplug and plug it somewhere else and notate.

State what percentage of a wave is displayed if the incoming wave frequency equals the LFF or HFF setting.

70%

Explain why filters should be used judiciously in EEG interpretations

It can block frequency waves which can lead to misinterpretation and changes of morphology and amplitude

Muscle (EMG) artifact

Electrical activity from the muscles that is caused by jaw clenching, facial movements, and body twitches. Variable in amplitude.

Muscle (EMG) artifact EEG description

Fast, irregular, high frequency, seen in frontal temporal electrodes, maximal over temporal. Variable in amplitude.

Define reference contamination

Experiencing artifact or need to repair

Define reactivity and 3 examples

Changes in frequency and amplitude in response to external stimulus.

PDR

Noxious stimulus

Ask pt questions to see if they are A&O

Define paper speed, sweep speed, and epoch

Paper speed- how fast the digital paper move across the screen (30mm/sec)

Sweep speed- the line moves across the screen in present time

Epoch- duration of time (10 sec/page)

You see a focal sharp transient maximal at F7 with a clear negative phase reversal between F7-T3 and a positive phase reversal at FP1-F7. Where is the likely focus and what is the likely cause

F7 & dipole

Alpha rhythm attenuates markedly with eye opening across 01-02 chains. What two terms describe this behavior?

Attenuation or alpha blocking and reactivity

A breach rhythm is suspected over C4 after a craniotomy. Which montage and filter adjustments could help confirm it?

Referential montage and raising sensitivity

A rhythmic 60 Hz artifact is present diffusely. List two steps to mitigate it/

Check impedance & ground

Environmental noise brief description

External sources caused by IV pumps, ventilators, and feeding pumps.

Environmental noise EEG description

Rhythmic, high frequency, low amplitude, irregular patterns

Environmental noise fixes

Check cable movement to amplifier and electrodes are secured

Electrode impedance imbalance brief description

Electrical resistant between electrodes can be caused by poor impedances, poor electrode placement, and electrical interference

Electrode impedance artifact EEG description

Higher resistant, large amplitudes, and poor signals

Electrode impedance imbalance fixes

Rescrub & reapply electrodes and check impedance

Sweating/salt bridge brief description

Caused by sweat and oily scalp

Sweat artifact EEG appearance

Slow baseline drift, large amplitude, and low frequency. Asynchronous.

Sweating.salt bridge fixes

Cool room & dry scalp

Electrical interference brief description

Caused by 60 hz or nearby electrical devices, broken ground, and poor impedances

Electrical interference eeg description

Uniform, sinusoidal, across multiple channels, broken ground, poor impedances, 60 hz frequency. It will look “fuzzy.”

Electrical interference fixes

Check and rebalance impedance and use notch filter as last resort

Muscle (EMG) artifact fixes

Ask pt to stop chewing and time lock with video

Eye movement/blink artifact brief description

Caused by bell’s phenomenon, PDR, and REM (slow baseline drift)

Eye movement/blink artifact eeg appearance

Large, slow, high amplitude bifrontal deflections (FP1/FP2), often symmetrical, no posterior field, lateral eye movement phase reversal (F7/F8)

Eye movement/ blink artifact fixes

Ask for a brief eye closure and ensure frontal electrodes are secure

Electrode popping/movement artifact brief description

Caused by looser electrodes which can lead to signal loss

Electrode popping/movement eeg description

Abrupt loss of signal, variable frequency and amplitudes in specific channels. It can look like a “positive phase reversal.”

Electrode popping/movement fixes

Rescrub & reapply electrodes or replace

A sweat artifact (slow drift) contaminates frontal channels. Name one setup fix and one post-acquisition setting to improve readability.

Increase air flow & reduce LFF

Eye blinks are contaminating FP1-F7 and FP2-F8. Name two strategies to reduce them during acquisition

Ask for brief eye closure and resecure frontal electrodes

A spike appears only at the end of a chain. After switching montages, it disappears. What does this suggest?

Artifacts

A generalized 3 Hz spike-and wave is suspected. Which montage and settings will best demonstrate its field and symmetry?

Referential montage because to see if i’s true and have the sensitivity 7 uv/mm