The document discusses various types of EEG artifacts and their origins, categorized as physiological and extraphysiological. It outlines key types of artifacts, such as cardiac, muscle, and ocular artifacts, including their identifying characteristics and potential resolutions for cleaner EEG recordings. The effects of external devices and bioelectrical potentials on EEG readings are also explored, emphasizing the importance of proper setup and monitoring during EEG procedures.

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