EEG artifacts are unwanted signals that can distort the interpretation of EEG recordings.
1. Environmental
Artifacts:
o Description: Environmental
artifacts result from devices in the patient's surroundings during EEG
recording.
o Causes: They can be due
to electrical fields surrounding devices or mechanical effects on the patient
or the patient's bed.
o Common Artifact: The most common
environmental artifact is caused by the alternating current (AC) present in the
electrical power supply.
o Frequency: Typically, at
60 Hz in North America and parts of South America and Asia, and 50 Hz in much
of the rest of the world.
o Amplitude: Usually medium
to low amplitude and may affect all channels or isolated channels with poorly
matched impedances.
2. Cardiac Artifacts:
o Description: The heart
produces two types of EEG artifacts - electrical and mechanical.
o Identification: They are
time-locked to cardiac contractions and can be identified by their
co-occurrence with complexes in the electrocardiogram (ECG) channel.
o Electrical Artifact: The electrical artifact is essentially the ECG as recorded from head electrodes, but it may not resemble a typical ECG due to distance and suboptimal axis for visualizing ECG complex details.
3. Electrocardiographic
(ECG) Artifacts:
o Description: ECG artifacts
are time-locked to cardiac contractions and can be mistaken for brain activity.
o Identification: They are best
identified by their co-occurrence with ECG complexes in the ECG channel.
o Characteristics: The electrical
artifact from the heart may not resemble a typical ECG due to distance and
suboptimal axis for visualizing ECG complex details.
4. Environmental
Artifacts:
o Description: Environmental
artifacts result from devices in the patient's surroundings during EEG
recording.
o Causes: They can be due
to electrical fields surrounding devices or mechanical effects on the patient
or the patient's bed.
o Common Artifact: The most common
environmental artifact is caused by the alternating current (AC) present in the
electrical power supply.
o Frequency: Typically, at
60 Hz in North America and parts of South America and Asia, and 50 Hz in much
of the rest of the world.
o Amplitude: Usually medium
to low amplitude and may affect all channels or isolated channels with poorly matched
impedances.
5. Muscle Artifacts:
oDescription: Muscle
artifacts are caused by electromyographic (EMG) activity, which is noise to
electroencephalographers.
oCharacteristics: EMG activity
obscures cerebrally generated EEG due to higher amplitude, confluence of
activity, and frequency overlap with EEG.
o Distribution: EMG artifact
commonly occurs in regions with underlying muscles, such as the frontalis and
masseter muscles.
o Frequency: EMG artifact
frequency is higher than most frequencies in clinical EEG and may appear as
beta frequency band activity or repetitive spikes.
Understanding the
characteristics and sources of EEG artifacts is crucial for accurate EEG
interpretation and diagnosis. Proper identification and differentiation of
artifacts from genuine brain activity are essential to ensure the reliability
of EEG findings in clinical practice.
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