Download ARTEFACT-EEG

FACULTE DE MEDECINE
UNIVERSITE ANTANANARIVO
Cours de DU en EEG clinique du 23/09/15
Les artéfacts en EEG
LA Rajaonarison, JG Lemahafaka, J Razafimahefa, AD Tehindrazanarivelo
USFR Neurologie
HU JRB
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Plan
• Introduction
• Artéfacts :
– Instrumentaux
– Électrodes
– Environnementaux
– Bioélectrique
– Potentielle évoquée
• conclusion
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Introduction
• Définition :
– Activité électrique d’origine non cérébrale
– 2 groupes :
• Physiologique (mouvements, bioélectriques, résistance cutanée…)
• Non physiologique (interférence électrique externe ou interne)
• Intérêts :
– Fait partie du quotidien
– Risque de mauvaise interprétation
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Introduction
• objectifs :
– Identifier la source de l’artéfact
– Reconnaitre les caractéristiques des différents types d’artéfacts
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Source d’artefact
Artefact physiologique (activités du corps)
1-Mouvements
• Tête
• Corps
• Scalp (battement artériel, contraction
musculaire)
2-Potentiel bioélectrique
• Changement (mouvements yeux, langue,
pharynx)
• Production (muscles scalp, cœur, sueur)
Artefact non physiologique
1-Interference électrique externe (autres énergie)
• Ligne électrique
• Équipements électriques
2- Dysfonctionnement électrique interne
•
•
•
•
Électrodes
Câble
Amplificateur
crayon, papier d’enregistrement
3-Changement de la résistance cutanée
• Activité glandes sudoripares
• Activité vasomotrice
• Transpiration
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Type d’artefact
• Instrumentaux
• Électrodes
• Environnementaux
• Bioélectrique
• Potentiel évoqué
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Artefacts instrumentaux
Source d’artefact
Caractéristiques
-circuit d’amplification
-apparait lors détection de silence
cérébrale (1-2µV)
-grapho-élément inhabituel (non
physiologique)
-corrosion / oxydation métal
-problème mécanique divers
• Poids pencil
• alignement
-distorsion de la morphologie et fréquence
des ondes cérébrales
-circuit tableau de bord (vibration, choque)
-pas d’enregistrement
-erreur de calibrage canal / paramètre de
filtrage
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Artefacts instrumentaux
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Artefacts d’électrode
Type
Caractéristiques
-limité à une électrode
-bref et transitoire :
• Électrode « pop », décharge spontanée
• artefact de pince (aile de papillon)
• mouvement du plomb
-une partie du scalp
-rythme de basse fréquence :
• Transpiration, ondulation d’onde lente >
2s
• Salt bridge, basse amplitude
• Artéfact de mouvement
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Electrode pop
The nearly vertical rise followed by the slower fall at the F3 electrode is typical of electrode pop artifact. Also typical is an amplitude
that is much greater than the surrounding activity, a field that is limited to one electrode, and repeated recurrence within a short time
Electrode Movement artifact
The focal slowing in the T4-T6 and T6-O2 channels has no field beyond T6 electrode and has the oscillations typical of
rhythmic electrode movement
Lead movement
Multiple channels demonstrate the artifact through activity that is both unusually high amplitude and low frequency
and also disorganized without a plausible field
Sweat artifact
The decreased amplitude and very low frequency oscillations are present diffusely, which is consistent with the whole
scalp’s involvement. The recurring sharp waves across most channels are ECG artifact.
Salt bridge artifact
Activity in channels that include left frontal electrodes is much lower in amplitude and frequency than the remaining background.
The lack of these findings when viewed in a referential montage confirms that an electrolyte bridge is present among the electrodes
involved.
Artefacts environnementaux
• Bruits électriques ambiants de 50 à 60 Hz
• Pousse seringue électrique
• appareils électriques : pompe électrique, téléphone
• effets mécaniques : ventilation mécanique, pompe
électrique
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60 Hz artifact
The very high frequency artifact does not vary and is present in the posterior central region, which does not typically
manifest muscle artifact. This example was generated by eliminating the 60Hz notch filter.
IV goutte
Triphasic and polyphasic transients are occurring simultaneous to the falling of drops in an IV infusion. This EEG
corresponds to electrocerebral inactivity.
Electrical motor
The very high frequency activity suggests an electrical source, and the fixed morphology and repetition rate indicate
an external device. This was caused by an electric motor within the pump.
Circulatory pump
Sharply contoured, b/l frontal repetitions occur with a fixed interval and are due to a pump providing circulatory
support and extracorporeal membrane oxygenation. Pulse artifact is present in multiple channels and most apparent
in the A2-T4 channel
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Artefacts bioélectriques
Type
Origine
-artéfact
cardiaque
-cardiaque (cœur / pacemaker)
-pulsation arterielle
-artefact
oculaire
-paupières
-OY / FY
-mouvement lent des yeux
-saccade occulaire
-artefact
musculaire
-Glossokinétique
-Photomyogénique
-EMG (scalp / muscle faciale)
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Artefacts cardiaques
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cardiac artifact
ECG artifact is identified by its fixed period and morphology and is limited to T3-A1 channel in this bipolar montage
Pacemaker artifact
Transients comprising very fast activity recur in channels with the A1 and A2 electrodes. The transients are
simultaneous to similar discharges in the ECG channel and correspond to a permanent pacemaker’s output
Pulsation
Focal slow waves at the left occiput follow each heart beat, as indicated in the ECG channel. The slow waves are
artifact due to electrode movement and were eliminated by repositioning the O1 electrode
Artefacts oculaire
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Blink artifact
Bifrontal, diphasic potentials with this morphology and field are reliably eye blink artifact.
Eye flutter artifact
Medium amplitude, low frequency activity that is confined to the frontal poles is identified as ocular artifact through
its morphology. Compared to blink artifact, flutter artifact typically has a lower amplitude and a more rhythmic
appearance
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Artefacts musculaire
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Muscle artifact
The high amplitude, fast activity across the b/l ant. region is due to facial muscle contraction and has a distribution
that reflects the locations of the muscles generating it. Typical of muscle artifact, it begins and ends abruptly.
Photomyogenic artifact
Simultaneous to the 6Hz strobe stimulations are transients across the frontal region that reflect an involuntary muscle
contraction.
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Conclusion
• Pas facile à éliminer
• Liste non exhaustive
• Collaboration :
– du technicien +++
– EEGer (expérience+++)
• Intérêt polygraphie
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Merci de votre aimable attention
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