EEG - Electroencephalography Artifact Identification Questions and Answers 1 — Questions and Answers
Question 1: A technologist observes rhythmic, sharp-appearing transients that are most prominent in the left temporal channels and perfectly time-locked with the QRS complex on the EKG monitor. What is the most likely artifact and the best initial step to resolve it?
- EKG artifact; attempt to reposition the M1/A1 or T3 electrode slightly. (Correct answer)
- Pulse artifact; increase the low-frequency filter to 2 Hz.
- IV drip artifact; check the patient's infusion pump for electrical noise.
- 60 Hz interference; ensure the notch filter is enabled.
Correct answer: EKG artifact; attempt to reposition the M1/A1 or T3 electrode slightly.
The artifact's morphology and perfect correlation with the EKG are classic signs of EKG artifact. This artifact is often most prominent on the left side because the heart's electrical field is strongest there. Slightly moving an electrode can change its orientation relative to the heart's electrical field, often reducing the artifact without altering the cerebral data.
Question 2: Which of the following EEG findings is most characteristic of a patient performing lateral eye movements to the right?
- A sharp positive deflection at F7 and a sharp negative deflection at F8.
- A slow positive deflection at F8 and a slow negative deflection at F7. (Correct answer)
- High-amplitude, synchronous slow waves in all frontal channels.
- Rhythmic 8 Hz sinusoidal waves in the Fp1 and Fp2 channels.
Correct answer: A slow positive deflection at F8 and a slow negative deflection at F7.
Due to the corneoretinal potential, the cornea of the eye is positively charged relative to the retina. When the eyes move to the right, the positive cornea moves closer to the F8 electrode, creating a positive deflection, and further from the F7 electrode, creating a negative deflection. This results in a characteristic out-of-phase potential between the two electrodes.
Question 3: A patient is extremely anxious, resulting in contamination of the frontotemporal channels with persistent, high-frequency, irregular activity. Which of the following is the MOST effective first step a technologist should take to reduce this artifact?
- Apply the 60 Hz notch filter.
- Increase the low-frequency filter setting to 5 Hz.
- Ask the patient to take a deep breath, relax their jaw, and let their mouth open slightly. (Correct answer)
- Re-prep the affected electrodes to lower their impedances.
Correct answer: Ask the patient to take a deep breath, relax their jaw, and let their mouth open slightly.
The described artifact is electromyographic (EMG) or muscle artifact, often from tension in the frontalis and temporalis muscles. The most effective initial intervention is to use relaxation techniques to reduce the muscle activity at its source. Asking the patient to relax their jaw is a direct and often successful method for reducing this specific artifact.
Question 4: During an EEG on a febrile and diaphoretic patient, the technologist observes very slow, undulating, low-frequency (<0.5 Hz) waves that are widespread and cause the baselines of multiple channels to sway. This pattern is most characteristic of which type of artifact?
- Respiration artifact
- Glossokinetic artifact
- Pulse artifact
- Sweat artifact (Correct answer)
Correct answer: Sweat artifact
Sweat (perspiration) changes the electrical properties and conductivity at the skin-electrode interface. This change in impedance creates very slow, rolling baseline sway, also known as galvanic skin response (GSR), which is consistent with the described pattern.
Question 5: An EEG recording shows a sudden, very high-amplitude, brief transient that is strictly confined to a single channel. The transient does not have a physiological field and is not time-locked to any other event. What is the most likely cause?
- An EKG artifact
- An epileptiform spike
- An electrode artifact ('pop') (Correct answer)
- A photic driving response
Correct answer: An electrode artifact ('pop')
The key features are its confinement to a single electrode and the lack of a physiological field (i.e., it doesn't appear in adjacent channels). This is the classic presentation of an electrode artifact, often called an 'electrode pop,' which is caused by a sudden, unstable change in impedance at that one site.
Question 6: Which of the following is the LEAST likely cause of persistent 60 Hz electrical interference in an EEG recording?
- A nearby unplugged piece of medical equipment in the room.
- The patient's rhythmic chewing or teeth clenching. (Correct answer)
- Unbalanced electrode impedances, with one being significantly higher than the others.
- A frayed power cord on the EEG machine or patient's bed.
Correct answer: The patient's rhythmic chewing or teeth clenching.
Chewing and teeth clenching produce electromyographic (EMG) artifact, which is high-frequency but is generated by muscle activity and is not locked to the 60 Hz power line frequency. The other options are all common sources of electrical interference that can introduce 60 Hz noise into a recording.
EEG - Electroencephalography Artifact Identification Questions and Answers 1
A technologist observes rhythmic, sharp-appearing transients that are most prominent in the left temporal channels and perfectly time-locked with the QRS complex on the EKG monitor.
What is the most likely artifact and the best initial step to resolve it?