1. EEG artifacts can originate from nonphysiologic sources like electrode movements, poor electrode contact, grounding issues, and environmental factors.
2. Common electrode artifacts include electrode pops, ground lead artifacts, and salt bridge artifacts which appear as unusual waveforms restricted to single electrodes.
3. Instrumental artifacts include 60Hz noise from power sources, electrostatic interference from cable movements, and electromagnetic interference from devices like phones, monitors, and stimulators.
4. Identifying the source and distribution of artifacts is important to distinguish them from actual brain activity.
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Artifact of nonphysiologic origin
1. EEG ARTIFACTS OF NONPHYSIOLOGIC ORIGIN
P.R.SAI PRASHANTH
FIRST YEAR DM PG
DEPT. OF NEUROLOGY
GRH-MADURAI
2. Electrode and Input Lead Artifacts
• Any unusual waveform that is restricted to a
single electrode should be considered to be
artifactual.
• Poor electrode contact or “loose” electrodes are
a frequent cause of artifact
• These electrode movements may be minute and
not well seen by visual observation
3. POPS
• Monophasic discharges
• mirror images” of the discharge seen in bipolar
channels with the electrode in common
• Reason: Poor Connection leading to impedence
mismatch and 60Hz susceptibility
4. Electrode pop is noted over the P4 electrode, most prominent in the
area of skull breach, which
evolves into faster, almost ictal-appearing discharges.
5. Electrode pop imitating a very localized seizure. The Fp1 electrode is not well placed
or has air-dried
paste. Rhythmic 5-Hz activity remains quite focal but then slows to 4 Hz almost
“evolving.”
6. Why not Pathological?
• Restriction to a single electrode contact.
• Normal records in nearby leads
7. Ground Lead artifact
• Ground lead recordings occur when a high
impedence lead(due to poor contact) in a
bipolar montage is substituted by ground
electrode.
• Bizzare waveforms
8. Ground lead recording. Very high impedance electrode at O1 causes ground electrode (at Fpz) to
become input 2 of channels including O1. Therefore, T5-O1 effectively becomes T5-Fpz, resulting
in “upside down”
eye blinks (arrows) in this channel.
9. Salt bridge artifact
• Due to a connection between two leads
• flat or even isoelectric.
• Reason: Summation of two lead potentials as
1 lead
10.
11. The T4 electrode acts as a “photocell” detecting the 9-Hz photic stimulus artifact. There is also
increased 60-Hz artifact in this high impedance channel when the photic stimulator is active.
12. Incorrect Jack artifact
• Occasionally, the leads are placed into the
incorrect jack inside the headbox and can
yield unusual fields
15. 60 Hz Artifact
• 60-Hz artifact can be caused by a faulty or
absent ground connection to the patient, or
defects in the power supply or other parts of
the instrument
18. Electrostatic Artifacts
• Electrostatic forces may induce currents in
electrode wires or cables.
• Movement of the input cable between
electrode jack box and the amplifier can also
cause capacitive charges
• Prevention: Sorrounding wires with gauze
20. Figure 13.32 Ventilator artifact noted periodically with superimposed faster waves from water
vibrating inside the
tubing.
21.
22. Figure 13.34 Rhythmic activity over the right temporal region looks like a partial seizure until the
dialysis machine is turned off demonstrating machine artifact.
23. Electromagnetic Artifacts
• High-frequency interference from nearby television
and radio stations is rare but difficult to eliminate.
Artifact can be seen in all channels. Hospital paging
systems and walkie-talkies using radio frequency
carriers may also cause artifact.
24. Figure 13.35 Two-second burst of 30 cycle/ sec telephone artifact (electromagnetic artifact,
vertical arrow) diffusely,
but highest amplitude in high impedance electrode Fp2. This leads to eye movements and EMG
as the phone
is answered, obscuring a second “ring artifact.”
25. Electric Stimulators
• Pacemakers produce very spiky, usually high-
voltage artifact
• These spikes are best seen in the EKG channel,
but may occasionally show a field extending to
EEG electrodes
