EEG - Electroencephalography Electrode Placement and Montages Questions and Answers 1 — 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?
- Nasion, inion, and both mastoid processes
- Nasion, vertex, and both temporal lobes
- Nasion, inion, and both preauricular points (Correct answer)
- Vertex, inion, and both zygomatic arches
Correct answer: Nasion, inion, and both preauricular points
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?
- Bipolar 'double banana' montage
- Referential montage (Correct answer)
- Laplacian montage
- Transverse bipolar montage
Correct answer: Referential montage
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?
- In chains running from the left to the right side of the head.
- To a single common reference electrode, such as the vertex (Cz).
- In chains running from anterior to posterior regions of the head. (Correct answer)
- Each electrode is compared to a weighted average of its surrounding electrodes.
Correct answer: In chains running from anterior to posterior regions of the head.
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?
- It measures the voltage difference between each electrode and a mathematically derived average of all electrodes.
- It is designed to be less sensitive to localized abnormalities compared to referential montages.
- It measures the voltage difference between adjacent electrodes in a chain. (Correct answer)
- It requires a non-cephalic reference to avoid contamination from brain activity.
Correct answer: It measures the voltage difference between adjacent electrodes in a chain.
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?
- Laplacian montage (Correct answer)
- Contralateral ear reference montage
- Longitudinal bipolar montage
- Average reference montage
Correct answer: Laplacian montage
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.
Question 6: According to the 10-20 International System nomenclature, which electrode would be located over the left mid-temporal region?
- T4
- T3 (Correct answer)
- C3
- Pz
Correct answer: T3
In the 10-20 system, the letter indicates the underlying brain region ('T' for Temporal) and the number indicates the hemisphere. Odd numbers are used for the left hemisphere and even numbers for the right hemisphere. 'z' denotes the midline. Therefore, T3 is the electrode over the left mid-temporal region.
EEG - Electroencephalography Electrode Placement and Montages Questions and Answers 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?