EEG - Electroencephalography Electrode Placement and Montages Questions and Answers

Question 1

An EEG technologist is setting up for a routine adult EEG. According to the International 10-20 System, what are the four primary anatomical landmarks used to ensure standardized and proportional electrode placement?

Accepted Answer

Nasion, inion, and both preauricular points

Answer

The International 10-20 System relies on four key anatomical landmarks for its measurements: the nasion (bridge of the nose), the inion (bony prominence at the back of the skull), and the left and right preauricular points (depressions just in front of the ears). These points form the basis for all subsequent measurements, ensuring that electrode placement is proportional to the patient's head size and shape.

Question 2

A patient's EEG recording shows a focal discharge. To best define the point of maximum electronegativity and pinpoint the origin of the activity, which type of montage is most effective?

Accepted Answer

Referential montage

Answer

Referential montages compare the voltage of each scalp electrode to a single, common reference point. This configuration is particularly useful for determining the electrode with the highest amplitude abnormality, which helps to clarify the point of maximal electronegativity when it might be unclear on a bipolar view.

Question 3

In a longitudinal bipolar montage, often called a 'double banana', how are the electrodes connected?

Accepted Answer

In chains running from anterior to posterior regions of the head.

Answer

The longitudinal bipolar montage, or 'double banana', consists of chains of electrodes linked from front to back. For example, a temporal chain might connect Fp1-F7, F7-T3, T3-T5, and T5-O1. This arrangement is excellent for identifying phase reversals, which help localize the source of an abnormality between two adjacent electrodes.

Question 4

Which of the following statements accurately describes the fundamental principle of a bipolar montage?

Accepted Answer

It measures the voltage difference between adjacent electrodes in a chain.

Answer

The core principle of a bipolar montage is the measurement of the potential difference between pairs of adjacent electrodes. These pairs are linked together to form chains, which can run anterior-posterior (longitudinal) or left-right (transverse). This method is effective for localizing focal events by identifying phase reversals.

Question 5

A technologist is reviewing an EEG on a digital system and wants to enhance the visualization of a very localized, focal discharge while minimizing the influence from distant, widespread activity. Which montage would be the most appropriate choice?

Accepted Answer

Laplacian montage

Answer

The Laplacian montage, also known as a source derivation or local average reference, is specifically designed to highlight focal activity. It calculates the voltage at each electrode relative to a weighted average of its immediate surrounding electrodes. This technique enhances localized events and reduces the effect of widespread or distant electrical fields.

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Electrode Placement and Montages Questions and Answers