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  • 1. Introduction:
    • Unwanted electrical activity arising from different sources, other than cerebral activity
    • EEG -highly sensitive recording device, easily interrupted by other electrical activity of very high voltages
    • Some readily distinguished, others closely resemble cerebral activity .
  • 2. Principles used to discriminate artifacts from EEG signals:
    • Physiological activity has a logical topographic field of distribution with an expected fall off of voltage potentials.
    • Artifacts have an illogical distribution that defies the principles of localization
  • 3. Classification:
    • Physiological : from patient’s own physiological generator sources other than the brain
    • Extraphysiological : Externally generated e.g. instrumental & environmental
  • 4. Physiological artifacts:
    • Cardiogenic-electrical
    • mechanical
    • Muscle activity
    • – Eye movement
    • – surface EMG
    • – Movement
    • glossokinetic
    • respiration
    • photomyoclonic
    • Skin artifacts
    • perspiration
    • salt bridges
    • Eye movements
    • Blink
    • flutter
    • Lateral gaze
    • Lateral rectus spike
    • Slow eye movements
    • Electroretinogram
    • REM sleep
  • 5. Eye movement artifacts:
    • most common, due to cornea-retinal potentials. The cornea is positive to the retina by 50-100 mv
    • Fp1, Fp2, F7, F8 , amplitude is approx 50- 200uv
    • frontopolar rhythmic slow wave activity - simulating brain activity
    • Types of eye movement artifacts
    • – Eye open, eye closure and blink
    • – Eyelid flutter
    • – Eyeball movement (lateral, vertical and oblique eye movements
  • 6. Eye opening and eye closure
  • 7. Blink Eye blink is a “U” shape transient potential which appears in frontopolar electrodes which are closer to the eyes.
  • 8. Eyelid flutter Fine eyelid movements may produce rhythmic 4-8 Hz activity in the frontal leads (disappear on fixation)
  • 9. Lateral eyeball movements
  • 10. Elimination:
    • close the eyes or eye fixation
    • close his eyes with his fingers or place a soft cloth or a cotton pads over the closed eyelids
    • Monitoring eye movements by placing extraocular electrodes will easily help to distinguish from frontal slow waves
  • 11. Muscle (EMG) artifacts:
    • EMG artifacts are due to the muscle contraction
    • superimposed upon the EEG activity
    • The motor unit potentials (MUPs) arising from
    • the scalp muscles may cause misinterpretation by
    • resembling spike or cortical β-activity
  • 12. Lateral rectus spikes:
  • 13. Frontalis:
  • 14. Temporalis: Clenching and grinding teeth
  • 15. Swallowing: Swallowing of saliva usually produces a short burst activity
  • 16. Chewing:
  • 17. Sniffling artifact: Small EMG component with a slow wave
  • 18. Facial myokymia:
  • 19. Glossokinetic artifact: Movement of the tongue during speaking may produce synchronous intermittent rhythmic EEG activity (2-6 Hz) because the mass of the tongue acts as a charged body with a negative tip
  • 20. Glossokinetic artifact:
  • 21. Tremor:
  • 22. Differentiation between EMG artifacts & the cortical spikes :
    • EMG potentials are of extremely short duration (2-20 msec) and spiky even on increasing paper speed to 60 mm/s
    • On basis of morphology and frequency
    • During sleep EMG activity is reduced whereas cortical spikes increase
    • Document using extra muscle electrodes
  • 23. Reduction/elimination:
    • Frontalis - close eyelids lightly and relax
    • Temporalis - opening the mouth
    • Use of relaxation techniques (reassuring, comforting the patient),Massaging the particular muscle groups
    • Occipitalis - putting the pillow under the neck
    • As a last resort change the high frequency filter to 35/15 Hz
  • 24. Cardiogenic artifacts:
    • EP arising in the cardiac muscles, high in amplitude
    • Spread to scalp by volume conduction
    • Prominent in babies, obese, short – neck, cardiomegaly
    • Referential montage picks up ECG artifact due to large interelectrode distances and close proximity of ear electrodes to the heart
    • Equipotential on the scalp - not picked up in bipolar montage
  • 25. Types:
    • ECG
    • Pulse
    • Pacemaker
  • 26. ECG Coming at regular intervals synchronising with ECG
  • 27. ECG: Coming at regular intervals synchronising with ECG
  • 28. Pulse
  • 29. Pulse:
  • 30. Elimination:
    • Changing the head position relative to the thorax
    • Lower the electrode resistance (A1 and A2) or use body earth (A1+A2)
    • Change reference to Cz
    • Shift the electrode a little - eliminate pulse wave
  • 31. Sweat artifact:
    • Warm and humid recording room
    • Anxiety and emotional tension
    • Autonomic dysfunction
    • Electrical potentials due to sweat glands
    • Reduction in the skin resistance (GSR)
    • NaCl and lactic acid of sweat may produce large base line sways
  • 32. Sweat: These are the slow waves of very low frequency (1/3-1/2 Hz)
  • 33. Salt bridge: Electrolyte in sweat interact with electrode gel / paste to produce a salt bridge
  • 34. Elimination:
    • Proper air conditioning
    • Reducing emotional stress
    • Sponging the patient’s face & forehead with alcohol/spirit
    • Setting the short time constant (LFF) if all the efforts fail
  • 35. Movement artifacts:
    • Movement of head, body and limbs produce irregular high voltage potentials
    • Movement of the head during HV or respiration can produce occipital electrode artifacts
    • Movement associated with seizure may obscure cerebral activity
    • Artifacts may occur in essential tremors, Parkinson disease and other movement disorders
  • 36. Head movement: Movement between the head and the pillow
  • 37. Movement associated with seizure: Contraction of skeletal muscles before the seizure activity starts
  • 38. Movement associated with seizure: Difficult to determine the origin of the seizure activity
  • 39. Patting artifacts: Mother patting baby
  • 40. Respiration artifacts: More commonly seen during HV as slow wave activity
  • 41. Reduction/elimination:
    • Solicit the co-operation of the patient to be calm and still
    • Changing the position or turning the patient over will diminish tremor artifacts
    • Placing a roll of towel or firm material under the neck may do away with respiratory artifacts
  • 42. Extra physiological artifacts:
          • Electrode –electrode pop, contact
          • Technical-lead movement, placement
          • Instrumental –AC 60hz artifact ventilator, circulatory pumps
          • Iv fluids
          • Environmental-mobile, TV, radio, electromagnetic
  • 43.
    • The scalp-electrode junction is an important and delicate link in the whole system
    • Electrode artifacts occur due to the change in the resistance or electrode potential between the scalp and the electrode
    • Poor contact, improper electrolyte application, broken lead, poor contact at the junction box, dry out of electrode paste
    Electrode artifacts:
  • 44. Electrode pop: A sudden change in the electrical potential between the electrode and scalp gives rise to the ‘pop’
  • 45. Electrode artifact: Loose contact of the electrode with the scalp
  • 46. Electrode movement artifact: This is movement of electrode on the scalp, because of excessive jelly
  • 47.
    • Recognition & differentiation from cerebral activity:
    • Electrode artifact is strictly confined to one lead or channels having input from this electrode, where as cerebral activity would usually spread to the adjacent electrodes
    • In a bipolar montage, the artifacts show mirror images (like phase reversals) in two adjacent channels
    • Wave morphology may change from time to time
    Electrode artifacts:
  • 48.
    • Elimination
    • Applying proper electrolyte
    • Check electrode impedance & continuity
    • Change the electrode
    • If it still present change the position at a distance of 0.5-1cm
    Electrode artifacts:
  • 49.
    • due to the malfunctioning of certain parts of the machine
    • -Pen deflection
    • -Amplifier
    • -Galvanometer
    • -Faulty ground
    • -Photic stimulator
  • 50.
    • Non-symmetrical electrode placement
    • Erroneous settings of different channels
    • Unequal electrode impedances result in loss of common mode rejection and recording of AC artifact
    Technical artifacts:
  • 51. Pen deflection:
  • 52. A1- disconnected:
  • 53. Photic:
  • 54.  
  • 55. Interchanging electrode placement: Interchanging the Fp2 electrode with O2
  • 56. AC artifact:60 hz artifact Very high electrode impedance of more than 25 k 
  • 57.
    • troublesome as they cannot be easily controlled by the technologist
    • Movement of other persons
    • Types of environmental artifacts:
    • – Electromagnetic Interference
    • – Electrostatic Induction
    • – Radio frequency Interference
    • As technology expands – new artifacts appear
      • Mobile phone artifacts
    Environmental artifacts:
  • 58. Electromagnetic interference:
    • Current flowing through an electrical conductor (main power supply), produces a magnetic lines of force around the conductor
    • The greater the current, the stronger the field
    • Occurs between mains and patient or electrode attached to the scalp or junction box
    • Common sources – power transformers
      • Electric motors in lifts, fans, air-conditioners
    • AC interference (result of capacitance or inductive effects on wires leading from the scalp to the junction box)
  • 59. Electrostatic Induction:
    • Opposite polarities of two charged bodies produces electrostatic induction when negative electric charge is applied
    • Presence of several instruments adjacent to the EEG machine (like fluorescent light, ventilators etc.)
    • Movement of any charged body near the patient (like plastic, rubber, synthetic fibres etc)
    • Often the technologist himself is the recipient of this discharge
    • Low electrical resistance between patient and the environment
  • 60. Static artifact: Produced by placing a charged synthetic paper near the patient
  • 61. Static artifact: walking in to collect a report
  • 62. Electrostatic artifact: Startle or clap response can also cause static artifact
  • 63. AC Interference
  • 64. Cell phone artifact:
  • 65.
    • Minimisation/removal of environmental artifacts:
    • Keeping electrode leads close together.
    • Move away from source (at least 10 feet)
    • (since electrostatic induction is inversely proportional to the distance between patient and source)
    • Changing the orientation of the patient/source parallel to the electromagnetic lines of force
    • Locate the EEG lab at least 50 feet away from AC feeders, transformers etc.
    • One earthing point common to all equipment
    • Shielding the source of artifact and machine with earthed metal shield
  • 66. Artifacts are also useful:
    • Slow lateral eye movements and disappearance or reduction of EMG are a valuable sign of drowsiness/sleep
    • Eye open and eye closure artifacts record the precise point where the patient opened or closed his eyes
    • Short bursts of EMG activity may mark the occurrence of myoclonic jerks
  • 67. Environment for artifact free recording
    • Quiet atmosphere
    • Comfortable bed
    • No synthetic carpeting
    • Convenient control of lighting
    • Proper earthing / shielding
    • Different power supply to equipment and air conditioner
    • Comfortable temperature and humidity levels to avoid sweating, tension, restlessness
  • 68.
    • Thank you