EEG Artifacts & How to Resolve (Lalit Bansal M.D.)
- 1. EEG Artifacts & How to Resolve Lalit Bansal M.D. Director of Epilepsy Surgery Medical Program Pediatric Epilepsy & Clinical Neurophysiology Children’s Mercy Hospital 05/15/2018
- 2. EEG records cerebral activity and electrical activities from sites other than the brain Anything that is NOT of cerebral origin is termed as ARTIFACT Types of Artifact: 1. Physiological artifact - generated other than brain ie. body 2. Extraphysiological artifact - arise outside the body, eg: equipment, enviornment Introduction
- 3. Physiological activity has a logical topographic field of distribution with an excepted fall of the voltage potentials Artifact have an illogical distribution that defies the principles of localization Principles to discriminate artifacts from EEG signals
- 4. Good, clean prep Balanced impedances Good hook-up, neatly bundled electrodes Place jack-box close to patients head Keep patient cool, not cold Unplug all electrical items close to patient, i.e. bed, radio, fan, etc. KEYTO AN ARTIFACT FREE RECORDING
- 5. Cardiac Electrode External device artifact Muscle artifact Ocular artifact Artifacts
- 6. Heart produce 2 types of artifact 1. Electrical 2. Mechanical Timed lock to cardiac contractions and synchronized with EKG complexes P/T wave are usually not visible on EEG (distance from the heart and the suboptimal axis) Artifact is a poorly formed QRS complex Prominent in patients with short neck Most prominent over temporal region R wave - A1 Negative and A2 Positive Cardiac Artifact
- 10. 5 Year old male with h/o arrhythmia
- 11. Generalized across the scalp, comprises high frequency, polyphasic potentials with a duration that is shorter than EKG artifact Pacemaker artifact 5 Year old male with h/o arrhythmia
- 12. Image of pulse artifact
- 13. Mechanical artifact from the heart arise through the circulatory pulse Electrode artifact - occurs when an electrode rests over a vessel Periodic slow wave with a regular interval - follows EKG artifact’s peak by about 200msec Most common over frontal and temporal, less common over occipital How to Identify: Applying pressure on electrode alters its appearance on the EEG Pulse Artifact
- 15. PULSE ARTIFACT
- 16. PULSE ARTIFACT
- 17. Mechanical cardiac artifact Results from slight movement of the head or body that occurs with cardiac contraction Similar to pulse artifact but is more widespread May involve one or few electrodes – due to electrode lead movement Biposterior electrodes if movement of the head on the pillow Occasionally can be generalized How to resolve: Reposition the head Ballistocardiographic Artifact
- 20. Types: 1. Electrode pop 2. Electrode contact 3. Electrode/lead movement 4. Perspiration 5. Salt bridge 6. Movement artifact
- 21. Usually manifest as one of two disparate waveforms, brief transients that are limited to one electrode and low frequency rhythms across a scalp region Due to spontaneous discharging of electrical potential present between the electrode or its lead Electrode pops - reflect the ability of the electrode and skin interface to function as a capacitor and store electrical charge across the electrolyte paste or gel that holds the electrode in place With the release of the charge there is a change in impedance, and a sudden potential appears in all channels that include the electrode Sometimes more than one pop occurs within a few seconds Characteristic morphology - very steep rise and a more shallow fall Electrode Pop
- 22. F3 electrode Pop
- 23. Produces artifact with a less conserved morphology than electrode pop Poor contact produces instability in the impedance, which leads to sharp or slow waves of varying morphology and amplitude These waves may be rhythmic if the poor contact occurs in the context of rhythmic movement, such as from a tremor. Poor electrode contact or lead movement
- 25. Reference Montage ipsilateral ear–T5 electrode activity
- 26. 60 Hz Off – high Impedance inT5
- 27. Lead movement has more disorganized morphology that does not resemble true EEG activity Often includes double phase reversal (without consistency in polarity that indicates a cerebrally generated electrical field) Lead Movement Artifact
- 28. Electrode Movement Artifact Slowing in T4-T6 and T6-O2 channels No field beyond T6 Oscillations typical of rhythmic electrode movement
- 29. Seen due to smearing of the electrode paste between electrodes or presence of perspiration across the scalp Forms an unwanted electrical connection between the electrodes forming a channel Perspiration artifact - manifests as low amplitude - undulating (smooth) waves - duration is typically greater than 2 sec Slat bridge artifact - lower in amplitude - not wavering with low frequency oscillation - typically include only one channel It may appear flat and close to isoelectric Salt Bridge and Perspiration Artifact
- 31. Sweat Artifact
- 33. TYPES : 50/60 Hz ambient electrical noise Intravenous drips Electrical devices: intravenous pumps, telephone Mechanical effects: ventilators, circulatory pumps
- 34. External devices produce EEG artifact through the electrical fields they generate or through mechanical effects on the body Commonly due to the alternating current present in the electrical power supply Medium to low amplitude and has the monomorphic frequency - 60 Hz in North America and 50 Hz in much of the rest of the world May be present in all channels or in isolated electrode with poorly matched impedances
- 35. 60 Hz Artifact
- 36. Electrical noise may also result from falling electrostatically charged droplets in an IV drip In-phase activity A spike like EEG potential results, which has the regularity of the drip EEG
- 37. Ventilators and circulatory pumps produce artifacts with slower components than other electrical devices Resemble ballistocardiographic or other electrode artifact Monomorphic frequency with fixed interval Slow wave or a complex including a mixture of frequencies superimposed on a slow wave Exceptions to typical pattern – High frequency oscillator Mechanical devices
- 41. Muscle artifact Types : Glossokenetic (chew/swallow) Photomyogenic (photomyoclonic) Surface Electromyographic (scalp/facial muscle)
- 42. Frequency is higher than that of clinical EEG and too fast to be visually estimated Without filtering, EMG artifact usually has a more disorganized appearance because the individual myogenic potentials overlap with each other Occasionally, individual potentials are discernible. Duration of EMG artifact varies according to the duration of the muscle activity; a second to an entire EEG recording. Artifact occurs most commonly in frontal and temporal electrodes Muscle Artifact
- 47. BIOELECTRICAL POTENTIAL Burst of slow waves with a diffuse distribution & muscle artifact in the temporal region!
- 48. GLOSSOKINETIC
- 50. Distinguishing from Ictal Activity Ictal epileptic activity Continuous glossokinetic artifact
- 51. Sucking Artifact 6 Month old male
- 55. Types : Blink Eye flutter Lateral gaze Slow/Roving eye movements Lateral rectus spike Rapid eye movements of REM sleep Electroretinogram Ocular Artifact
- 56. BATTERY 50- 100 mV Eye or eyelid movements
- 59. Fp1 – F7 Fp2 – F8 R L Rules of polarity
- 63. Fp1 – F7 Fp2 – F8 R L Rules of polarity
- 65. Eye Flutter Artifact w/ Infraorbital Electrodes
- 66. 1 2 1 1 1 2 Conjugate EM: Vertical Horizontal Out of phase EEG In-phase Out of phase In-phase Detect all EM Out of phase In-phase EEG = EM EEG = vertical EM Misses low amplitude EM Good because: Bad because:
- 68. VERTICAL
- 70. FAST COMPONENT TO THE RIGHT HORIZONTAL NYSTAGMUS
- 72. R L 3 T LATERAL RECTUS SPIKES
- 79. JITTERINESS EMG
- 80. SLOW BODY MOVEMENT/ JITTERINESS
- 82. Sympathetic Skin Response (Galvanic Skin Response) Skin potential medicated by unmyelinated cholinergic sympathetic fibers Changes in electrical properties of skin during sweating, sensory stimulation or emotional stress Appear as long lasting potential of abrupt onset with a monophasic, biphasic or triphasic morphology. Most commonly from frontal but may be diffuse Confirmation: extracranial recording from palm of the hand