EEG ARTIFACTS. USEFUL IN IDENTIFYING ARTIFACTS IN EEG RECORDING

1. ARTIFACTS IN EEG
DR LAVANYA 25/7/22

2. • In addition to the electrical activity of brain , EEG records the
potentials of non cerebral origin that are termed as ARTIFACTS

3. Characteristics of Artifacts
• Activity confined to a single channel in referential recording and 2
neighboring channels in bipolar recording
• Atypical generalized waveform potential
• Highly stereotypic and very monomorphic pattern
• Activity with very low (<1Hz) or very high (>70 Hz) frequency
• Atypical multiple phase reversal
• Periodic pattern with perfect regularity
• Distribution of activity over multiple electrodes without physiological
field

4. Types of Artifacts : Depending on their origin :
Physiological : Non physiological
1. Eye movements : 1. Instrumental artifacts
Horizontal , vertical eye movements 60Hz / 50 Hz artifacts, electrostatic, magnetic
Eye lid flutter
Electroretinogram
2. Cardiac artifacts: 2. Electrode artifacts:
ECG Artifacts, Electrode pop
Pulse artifacts, Impedance-related
Pacemaker artifacts, Electrode lead movement,
Ballistocardiographic artifacts Photic cell artifact
3.Electromyographic artifacts: 3. Environmental artifacts:
Lateral rectus spike Ventilator artifacts, IV drip artifacts, Bed percussion artifacts,,
Frontalis , temporalis ,occipitalis electromyogram, ECMO artifacts, cell phone artifacts
swallowing, chewing
photomyogenic
4. Glossokinetic
5.Galvanic skin response- salt bridge , perspiration
6.Physiological movements artifacts

5. OCULAR ARTIFACTS:
• Each eye acts as an inherent 100mV electrical dipole along the
corneal – retinal axis with cornea relatively positive compared to
retina .
• Asymmetric eye movement artifact occurs due to
1. decreased eye movement of 1 eye
2. absence of 1 eye / retina
3.asymmetric electrode placement
4. frontal skull defect

6. • BLINK:
• Vertical eye movements occur
with blinking (Bell’s
Phenomenon). When eye blinks
the cornea rolls up causing
positivity in Fp1 and Fp2
relative to F3 , F4
• Vertical eye blink are slow <
4Hz, appear on frontal (Fp1,
Fp2), symmetric between 2
hemispheres

7. • Repetitive eye blinking can
be confused with FIRDA
• However blink artifact
doesn’t occur over central
regions and disappear with
eye closure, which helps to
differentiate it from FIRDA

8. FIRDA-Rhythmic , high voltage , delta activity at 2-3 Hz, occurs in bursts for 2-6
seconds . Seen in toxic –metabolic encephalopathy.

9. • Ocular flutter:
• They are more rapid , rhythmic, low amplitude in alpha frequency range

10. Lateral eye movement

11. Try this ?
Eye movement to Right

12. Roving eye movements :
slow waves<1 Hz over frontal ,temporal with wavy baseline .

13. • Lateral rectus spike: detects motor action potential due to contraction of lateral
rectus. Low amplitude spike , preceding lateral eye movement over F7/F8

14. • Electroretinogram:
Intermittent photic
stimulation may produce
electroretinographic
artifact due to activation
of retinal cells by light.
Covering 1 eye during
photic stimulation will
abolish ERG

15. Cardiac artifacts
1.Electrocardiographic:
• They are caused by
electric dipole generated
by cardiac depolarization,
which consists of poorly
formed QRS complex,
usually diphasic and time
locked to cardiac
contraction
• Seen maximal over left
posterior head region , in
referential montages

16. • 2. Pacemaker
Artifact:
• High frequency ,
high amplitude ,
polyphasic with
distribution across
the scalp

17. • 3.Pulse Artifact:
• It occurs when an electrode is overlying a pulsating vessel. Appear as periodic
slow wave , seen in single electrode
• They occur typically 200-300 s following the QRS complexes
• Can be identified by touching the electrode
• Most commonly seen in frontal and temporal region, it should not be
confused with TIRDA
• 4. Ballistocardiographic artifact:
• It is a form of mechanical artifact due to movement of head with cardiac
contractions , often seen in wide pulse pressure.
• They are wide spread and generalized.

18. Pulse artifact

19. EMG Artifacts
• Produced by muscle
contractions, most commonly
in frontal and temporal
electrodes. They are high in
amplitude and frequency , can
be mistaken for beta activity
or repetitive spikes.
• They are sharper in contour
when compared with beta
waves and disorganized.
• High frequency filter can
attenuate artifacts

20. Chewing artifact

21. Chewing artifact

22. Bruxism

23. Photo myogenic response
• Photic stimulation elicit
repetitive EMG artifacts time
locked to flashes of light
• These occur in frontal areas ,
bilaterally , occur more often
with eyes closed.
• Photoparoxysmal response
occur over posterior head
regions and lasts even after
photic stimulation is
stopped.

24. What is photoparoxysmal response (PPR)?
• Red colored light and patterned field of vision produces PPR
• Response to IPS- photic drive: monophasic transients with lag of 80-
150 m sec, time locked to stimulus are seen
• Photomyogenic responses: frontal dominant, sharply contoured, time
locked to IPS
• Photoparoxysmal response: spike and wave forms occur twice during
same frequency of IPS

25. Photic drive

26. grade1

27. grade2

28. grade3

29. grade4

30. Glossokinetic artifact
• They occur due to tongue
movement, most common
on frontal leads. Tongue is
like a battery , tip is
electronegative and base
is positive
• Glossokinetic potential are
broad that drops from
frontal to occipital

31. Glossokinetic artifact

32. • Sucking artifact

33. Sweat artifact
• Sodium chloride and lactic acid
from sweat react with electrode
metal and produce huge slow
baseline deflections called
sweat artifacts.
• Low frequency (0.25-0.5Hz) and
>2 seconds

34. Physiological movement artifacts

35. Non physiological artifact
• 60/50Hz ambient
electrical noise:
• The most common
environmental artifact
is 50 Hz , produced by
electrical devices in
vicinity of patient like
poor electrode contact,
defective cables,
unshielded power
lines..

36. Electrode artifacts
Poor electrode contact can cause impedance variability resulting in
electrode artifact. They appear as sharp or slow waves of
heterogeneous morphology
• Electrode pop
• Electrode contact artifacts
• Electrode movement artifacts
• Perspiration
• Salt bridge artifacts

37. Electrode pop
• Characteristic morphology : Steep rise and right angle upshot with shallow fall , limited to
1 electrode without disturbing background.

39. Salt bridge artifact: smearing of electrode paste between electrodes produces
unwanted connection b/w electrodes. they are v low amplitude, frequency potentials
in single lead on bipolar montages , severe enough to be isoelectric line

40. Perspiration artifact: sweat contains electrolytes, leads to instability of electrical
potentials. Produces undulating, low amplitude waves, duration >2 sec, causes
adjacent channels to cross and appear as unstable baseline in multiple channels

41. • Photocell artifact : During IPS , high impedance in electrode over frontal regions cause brief
spike like transients that are time locked with flash. Each flash cause a minute photochemical
reaction and electrode acts as photic cell in presence of high impedance

42. Electrostatic artifacts
• The electrostatic charges on drops of fluid in IV drips may cause spike
like potentials coinciding with drops of infusion
• Artifacts from electric infusers . Dialysis machines
• They occur due to combination of static and piezoelectric current in
pumps , causing currents to flow into patient and then to electrode .

43. Intravenous drip artifact- periodic brief electrostatic potential on EEG.
Spike like transients with each transient corresponding to iv drop rate

44. Ventilator artifact: caused by changing magnetic fields within ventilator motor and
by movement of electrodes. They correlate with mechanical cycles of ventilator, seen
bilateral frontally.

45. CRRT artifact: rotation of motor within CRRT produces 5-12 Hz activity in multiple
electrodes and in ECMO artifact rhythmic 1-3 Hz square wave artifacts are seen.

46. Artifact from anti bed sore percussion bed

47. Telephone ring artifact- electromagnetic artifact

48. Artifact detection and rejection
• Use of band pass filters
• Manual Rejection of Artifact Segments
• Automatic Rejection of Artifact segments
• Automated Subtraction of Artifact

49. Let’s try some – what artifact is seen?

50. How many eye blinks are seen

51. How many artifacts are seen ?what are they