EEG Instrumentation and Calibration 5

Question 1

During EEG setup, electrode impedance is measured and found to be 28 kΩ on electrode F3. The appropriate action is to:

Accepted Answer

Re-prep the skin and reapply the electrode to reduce impedance

Answer

Standard acceptable electrode impedance is below 5 kΩ (some guidelines allow up to 10 kΩ); 28 kΩ is far too high and requires skin re-preparation and electrode reapplication.

Question 2

The 'sensitivity' setting on an EEG machine refers to:

Accepted Answer

The voltage per unit of pen or display deflection (e.g., µV/mm)

Answer

Sensitivity in EEG describes how many microvolts of signal produce a given deflection (e.g., 7 µV/mm), controlling the amplitude scale of the recording.

Question 3

Which filter setting should be used to reduce sweat artifact (very slow baseline drift) without significantly affecting EEG frequencies of interest?

Accepted Answer

Decrease the time constant (increase the low-frequency filter cutoff)

Answer

Sweat artifact is a very low-frequency (sub-1 Hz) drift; decreasing the time constant (raising the low-frequency filter) attenuates these slow potentials while preserving standard EEG frequencies.

Question 4

In digital EEG systems, the Nyquist theorem states that to accurately digitize a signal, the sampling rate must be at least:

Accepted Answer

Twice the highest frequency of interest

Answer

The Nyquist theorem requires a sampling rate of at least twice the highest frequency component to avoid aliasing artifacts in the digitized signal.

Question 5

A technologist is setting up a 32-channel digital EEG system. If the high-frequency filter is set to 70 Hz, what is the minimum adequate sampling rate to avoid aliasing?

Accepted Answer

140 samples/sec per channel

Answer

Per the Nyquist theorem, sampling at least twice the highest frequency (2 × 70 Hz = 140 samples/sec) is the minimum to prevent aliasing.

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Practice Test

EEG Instrumentation and Calibration 5