Study guide
5.3 Artifact Recognition & Elimination
ABRET Registered EEG Technologist R.EEG.T.
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1 Introduction & R.EEG.T. Exam Overview
1.1 R.EEG.T. Exam Facts 1.2 Eligibility & Pathways 1.3 Content Outline & Study Strategy
2 Neurophysiology & Instrumentation
2.1 Neuroanatomy & Neurophysiology 2.2 Electronics & Instrumentation 2.3 Montages & Derivations
3 Pre-Study & Patient Preparation
3.1 Patient History, Assessment & Safety 3.2 Electrode Application & the 10-20 System 3.3 Equipment Setup & Calibration
4 Performing the Study
4.1 Recording Technique & Documentation 4.2 Activation Procedures 4.3 Special Studies & Populations
5 EEG Patterns, Artifacts & Recognition
5.1 Normal EEG Patterns 5.2 Abnormal Patterns 5.3 Artifact Recognition & Elimination
6 Clinical Correlation & Seizure Disorders
7.1 Seizures, Epilepsy & Syndromes 7.2 Neonatal & Pediatric EEG Patterns 7.3 Neurological Disorders & EEG Correlation
7 Post-Study Procedures & Professional Practice
8.1 Post-Study Procedures & Documentation 8.2 Ethics, Safety & Professional Issues
8 Final Review & Test-Day Strategy
6.1 High-Yield Recap 6.2 Localization & Pattern Drills 6.3 Test-Day Strategy & Pitfalls
5.3 Artifact Recognition & Elimination
Key Takeaways Explain This Topic AI
Eye-movement artifact follows a fixed rule: vertical eye movement is largest at Fp1/Fp2, and the cornea is positive, so upward gaze deflects frontopolar electrodes one way and a blink the opposite of downward gaze.
ECG artifact appears as a regular sharp deflection time-locked to the QRS complex on the simultaneous ECG channel; a recorded ECG monitor channel is the technologist's primary tool to identify it.
60-Hz (mains) artifact is a uniform high-frequency contamination usually caused by high or unbalanced electrode impedance; the correct first action is to reduce and balance impedance, not to apply a notch filter.
Electrode pop is an abrupt high-amplitude vertical deflection isolated to a single electrode caused by an unstable electrode-gel-skin junction, corrected by re-prepping and re-applying that electrode.
The technologist's primary duty is to identify and physically eliminate artifact at the source; filtering is a last resort because it can attenuate or distort genuine cerebral activity.
Last updated: May 2026
Why Artifact Recognition Is a Core Technologist Skill
Artifact identification and elimination sits squarely in the Performing the Study domain and is one of the most heavily tested practical skills. An unrecognized artifact can be over-read as epileptiform or slowing, while reflexively filtering an artifact can erase real cerebral activity. The exam rewards a systematic approach: identify the source, prove it with a dedicated monitor channel where possible, eliminate it physically, and only filter as a last resort.
Artifacts divide into physiologic (generated by the patient's body but not the brain) and non-physiologic (generated by equipment or the environment).
Physiologic Artifacts
Artifact Appearance Source Correction
Eye blink / vertical eye movement High-amplitude slow deflection maximal at Fp1/Fp2 Corneoretinal dipole (cornea positive) Add eye-monitor electrodes; ask patient to fix gaze; identify, do not filter out
Lateral eye movement Phase reversal at F7/F8 (lateral rectus spike may precede) Eye rotation Recognize with eye leads; benign
Muscle (EMG) Brief, very high-frequency spiky activity, temporal/frontal Scalp/jaw muscle tension Reposition patient, relax jaw, apply heat; HF filter only as last resort
ECG (EKG) Regular sharp deflection time-locked to QRS Cardiac electrical field Compare to recorded ECG channel; reposition reference; cannot remove physiologically
Pulse Slow wave ~200-300 ms after each QRS, single electrode Electrode over a pulsating vessel Reposition the offending electrode slightly
Sweat (salt-bridge) Very slow, low-frequency (<0.5 Hz) wandering baseline sway Electrolyte/perspiration Cool the patient, dry the scalp; raise LF filter only if needed
Glossokinetic Slow waves frontotemporal, with tongue movement Tongue acts as a dipole (tip negative) Ask patient to stop speaking/swallowing; have patient say "la-la" to confirm
Respiration / chewing / tremor Rhythmic activity time-locked to breathing, chewing, or tremor frequency Body movement Note the activity; add a monitor or annotate the behavior
The corneoretinal dipole rule is high-yield: the cornea is electrically positive relative to the retina, so vertical eye movements produce large, predictable, in-phase deflections at the frontopolar electrodes. A dedicated eye-monitor channel lets the technologist prove an Fp deflection is ocular and not frontal delta or a frontal spike.
Non-Physiologic (Technical / Environmental) Artifacts
Artifact Appearance Cause Correction
60-Hz (mains) interference Uniform thick high-frequency band at 60 Hz (50 Hz outside North America) High or unbalanced electrode impedance; nearby electrical equipment Reduce and balance impedances; remove/unplug interfering devices; notch filter is a last resort
Electrode pop Abrupt high-amplitude vertical deflection, isolated to one electrode, with sudden onset/offset Unstable electrode-gel-skin junction Re-prep skin, re-apply electrode, re-gel; check connector
Electrode/lead movement Irregular high-amplitude transients with patient or wire movement Loose electrode or swinging lead wire Secure electrode and braid/anchor wires
External device Regular periodic spikes (IV pump, ventilator, bed) Equipment in the recording environment Identify the device, isolate or unplug it, annotate
Static / triboelectric Random transients with people/blanket movement near the patient Static electricity Reduce movement near the head box, control humidity
60-Hz Artifact: the Classic Exam Trap
The correct first response to 60-Hz contamination on one or a few channels is not to apply the 60-Hz notch filter. The notch filter masks the symptom and can distort nearby fast activity. The correct sequence is:
Check and lower the impedance of the affected electrode(s) to a balanced value (typically <5,000 ohms and matched).
Confirm the electrode is properly applied and the connection to the headbox is secure.
Remove or move nearby electrical equipment.
Only after physical correction fails should the notch filter be applied, and that fact should be documented.
Widespread 60-Hz on every channel often points to a bad common reference or ground , not 21 individual bad electrodes.
A Systematic Method for Distinguishing Artifact From Cerebral Activity
The technologist should run a quick mental checklist before accepting a waveform as cerebral:
Field/distribution: Does it have a logical, gradient electrical field, or is it isolated to a single electrode (favoring electrode pop) or following a non-cerebral generator (eyes, ECG)?
Time-locking: Is it time-locked to the ECG (cardiac/pulse), respiration, a tremor, or an external device? A simultaneous ECG monitor channel is the single most useful artifact-identification tool.
Reproducibility on maneuver: Ask the patient to blink, look side to side, clench the jaw, swallow, or say "la-la" — if the suspect waveform tracks the maneuver, it is artifact.
Frequency signature: Pure 60 Hz, or muscle activity far faster than any physiologic rhythm, betrays a non-cerebral source.
Reactivity: Cerebral rhythms react to eye opening, alerting, and state changes; many artifacts do not, or react to a different stimulus.
Filtering Is the Last Resort
A recurring exam principle: filters change the displayed signal and can attenuate or distort genuine cerebral activity. The high-frequency (low-pass) filter reduces muscle artifact but also blunts spikes; the low-frequency (high-pass) filter reduces sweat sway but also attenuates slow cerebral delta; the notch filter removes 60 Hz but can ring and distort fast activity. Always correct the artifact at its physical source first and document any filter changes so the interpreting physician knows the displayed signal was modified.
Clinical Application
When artifact appears, the exam-correct workflow is: recognize it, prove it with a maneuver or monitor channel, fix the patient or electrode physically, re-prep impedance, and only then consider a filter — annotating everything you did so the record remains trustworthy.