Eeg artifacts

Eeg artifacts- Dr Pallav JAIN

1. Artifacts in EEG

2. EEG artifacts are recorded signals that are non-cerebral in origin. They may be divided into one of two categories: physiological artifacts non- physiological artifacts.  

3. Physiological artifacts arise from a variety of body activities that are due to either: Movement of head, body or scalp (e.g. pulsations of the scalp arteries )- that affect the electrode scalp interface Bioelectrical potentials generated within the body from moving sources (such as eye, tongue, or pharyngeal muscle movement), stationary sources such as the scalp muscles, heart or sweat glands Altered volume conduction due to changes in the conductance of tissues ( scalp, bone, muscle) and fluids (CSF, blood) between the cerebral cortex and the recording electrodes.

4. Non- physiological artifacts arise from two main sources: external electrical interference from other power sources such as power lines or electrical equipment, internal electrical malfunctioning of the recording system, arising from recording electrodes (electrode integrity, positioning and application), cables, amplifiers .

5. Artifacts can often be recognized by their characteristic morphology and distribution . The patient and record must both be closely observed throughout the recording  

6. Blinking and other eye movements. These movements cause potential changes which are picked up mainly by frontal electrodes. The electrodes that record the largest potential change with vertical eye movement are Fp1 and Fp2 because they are placed directly above the eyes. The electrodes that record the largest potential change with horizontal (lateral) eye movements are F7 and F8 because they are closest electrodes that are approximately lateral to the eyes .

7. Eye movement artifacts in the EEG can usually be identified by their frontal distribution, their bilateral symmetry and their characteristic shape . Eye movement artifacts can be identified during the recording by observing the patient and correlating eye blinks and movements with pen deflections.

8. Blink artifact- Fp1, Fp2

9. Flutter artifact

10. Flutter artifact Medium amplitude, activity confined to frontal poles Compared to blink artifact, flutter artifact typically has a lower amplitude and a more rhythmic appearance(more frequency)

11. Lateral eye movements F7 , F8

12. Slow rhythmic waves < 1 H z frequency Lateral frontal/ anterior temporal leads Appear as a wavy baseline

13. Lateral rectus spike

14. Muscle artifact Muscle activity causes very short potentials which usually recur. Muscle artifacts from scalp and face muscles occur mainly in the frontal and temporal regions. Easily identified by its shape and repetition. It can be reduced and often eliminated by asking the patient to relax the jaw or open the mouth slightly, or change position.

15. Muscle artifact

16. Muscle artifact H igh amplitude, fast activity. Distribution that reflects the locations of the muscles generating it . Typical of muscle artifact, it begins and ends abruptly .

17. Perspiration artifacts consists of slow waveforms that are usually greater than 2 sec in duration. In addition, sweat gland activity produces slowly changing electrical potentials that are recorded by the electrodes. Perspiration artifact almost always appear in more than one channel, but may be lateralized or asymmetric.

18. Sweat artifact

19. Electrocardiogram. The artifact may appear in all channels using a common reference. Or only in one or a few channels. Small amplitude artifacts reflects mainly the R- wave of the electrocardiogram .

20. The R- wave usually appears maximally over the left posterior head region as a positive sharply contoured wave form and, with lower amplitude, over the right temporal head regions as a negative waveform.  

21. If there is any doubt whether sharp waves are due to the ECG artifact or to the cerebral activity, the technician should record the ECG in one channel and compare it with the timing of the suspected sharp waves.

22. Pace maker Artifact

23. Pulse artifact Periodic waves of sinusoidal or triangular shape may be picked up by an electrode on or near a scalp artery as a result of pulse waves producing slight changes of the electrical contact between electrode and scalp with each dilation and contraction of the artery.

24. Electrical Interference .   Artifacts due to electrical interference emanates from electrical equipment and nearby power lines. Strong interference can cause artifacts even with good recording electrodes and equipment ; these artifacts are then likely to appear in all channels of all recordings made in the same recording room.

25. When recordings are made in an environment with excessive interference such as an intensive care unit or an operating room, the patient’s head and the connections to the EEG machine should be kept as far from power cables as possible . Electrode wires should be straightened and bundled together. Equipment other than the EEG machine should be unplugged if feasible.

26. Mechanical ventilator artifacts

27. Artifacts arising from electrodes A common electrode artifact referred to as an ‘electrode pop’ is due to a sudden change of electrode contact causing pen deflections which abruptly deviate from the baseline and then gradually return .

28. Electrode pop

29. Electrode pop N early vertical rise followed by the slower fall at the F3 electrode is typical of electrode pop artifact . A mplitude that is much greater than the surrounding activity, a field that is limited to one electrode .

30. Electrode movement artifact

31. Electrode movement artifact f ocal slowing in the T4-T6 and T6-O2 channels oscillations typical of rhythmic electrode movement poor contact which leads to sharp or slow waves of varying morphology and amplitude .

32. Lead movement

33. Lead movement A rtifact through activity that is both unusually high amplitude and low frequency and also disorganized without a plausible field Lead movement has a more disorganized morphology that does not resemble true EEG activity in any form

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