Fisch EEG Primer Chapter 3 Flashcards

Digital and Analog EEG instruments: parts and functions

1
Q

EEG frequency range of greatest clinical significance

A

0.5-30Hz

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2
Q

Aliasing results from..

A

sampling analog signals LESS than at least TWICE (Nyquist theorum and rate) as fast as the fasted freqency contained in the analog signal.

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3
Q

Difference between the electrode input board (aka jackbox, input box) of an analog vs. digital EEG instrument

A

analog: receives input and then transfers to amplifier
digital: receives AND amplifies signal before sending to computer monitor

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4
Q

Each channel of the EEG recording is producted by the output of one differential amplifier which measures…

A

difference in voltage between its two input terminals. Negative differences (greater negativity at input 1 compared to input 2)deflect UPWARDS and positive difference (greater negativey at input 2 compared to input 1) deflect DOWNWARDS.

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5
Q

Digital Filtering involves…

A

suppression of waveforms in selected frequency ranges

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6
Q

Montage reformatting involves..

A

retrospective changing of the displays montage

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7
Q

Purpose of EEG amplifiers (2)..

A
  • differential discrimination of differences in electrical potnetial of input 1 and 2
  • amplify size of potential differences
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8
Q

Differential discrimination/amplification (performed by amplifiers) involves

A

inputs 1 and 2 are essentially amplified in opposite directions from the amplifier ground, and effectively subtracted

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9
Q

In differntial amplification, a single waveform output can be the result of

A

an infinite number of different inputs

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10
Q

What is the difference between impedence and resistance

A

resistance involves direct (constant voltage) while impedence involves alternating currents.

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11
Q

60 Hz interference can be seen when…

A

unequal electrode impedence is present - most commonly results from loss of contact between electrode and scalp

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12
Q

Absent or ineffective ground connection results in…

A

lack of reference to polarize inputs 1 and 2 and results in amplication of artifacts that would otherwise be ignored
NOTE: does not protect patient from electrical shock

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13
Q

Amplification is characterized in terms of sensitivity which is measured by…

A

sensitivity: microVolts/mm (typical 7)

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14
Q

Low frequency filter (a.k.a. High pass filter)

A

reduces the amplitude of slow waves - decreases amplitude of selected frequency range 20-30% and then logarithmic filtering at even lower frequencies

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15
Q

High frequency filter (a.k.a. Low pass filter)

A

reduces the amplitude of fast waves - decreases amplitude of selected frequency range 20-30% and then logarithmic filtering at even higher frequencies

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16
Q

Notch filter

A

selectively reduces a narrow frequency range in order to remove electrical interference (i.e. in North America typically set to 60Hz)

17
Q

Three key attributes that determine how wll an analog to digital converter (ADC) will work…

A

1) sampling rate
2) number of amplitude levels (amplitude resolution) that can be resolved
3) input voltage range