Instrumentation and Calibration Flashcards

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

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

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.

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

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

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.

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

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

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.

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

Answer: Twice the highest frequency of interest

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

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?

Answer: 140 samples/sec per channel

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

Which of the following best describes the function of a referential (monopolar) montage in EEG recording?

Answer: Each channel records the difference between one active electrode and a common reference

In a referential montage, each channel compares one active scalp electrode to a single common reference electrode (such as Cz, ipsilateral ear, or average reference).

When a square wave calibration signal shows 'ringing' or oscillations after the rising edge, this most likely indicates:

Answer: The high-frequency filter cutoff is set too high, allowing high-frequency resonance

Ringing after the rising edge of a square wave indicates the high-frequency filter cutoff is set too high, allowing the amplifier to pass and amplify resonant high-frequency components at the step transition.