EEG Artifacts

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

18. BallistocardiographicArtifact

19. Electrode 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

32. External device 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

39. Ventilator Artifact

40. Telephone Ring Artifact

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

43. FRONTALIS
TEMPORALIS
OCCIPITAL
FACIAL
MASTICATORY
SUBMENTAL
CHIN

45. Glossokinetic 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

54. Pontine
lesion
Tinnit
us

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

58. Eye Blink Artifact

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

75. PHOTIC STIMULATION

76. ¾
a
b
PHOTIC
STIMULATION
10-15 msec
30-50 msec
ELECTRORETINOGRAM

79. JITTERINESS EMG

80. SLOW BODY MOVEMENT/ JITTERINESS

81. SOBBING
(shuddering)

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

83. SYMPATHETIC SKIN
RESPONSE
PALM
DORSUM