Unsual pattern of artefact

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rgmathew
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Joined: Wed Jun 22, 2016 4:57 pm

Unsual pattern of artefact

Post by rgmathew » Wed Jun 22, 2016 5:14 pm

I am measuring auditory evoked potentials in subjects with a cochlear implant. I am using a biosemi active 2 system with 64 channels (two 32-pin electrode sets). I am able to get the offset values within range on all the channels.

The implant produces a large electrical artefact but in most cases can be reduced with filtering/ICA etc. With a certain cochlear implant device I have noticed an unusual pattern of artefact consistently which is difficult to remove: there is a large artefact on the side of the head with the implant which can extend all the way to the midline. So for example If there is a right cochlear implant there can be a large artefact up to and including Cz but all of the channels including for example the C1 on the other 32-pin set are typically artefact free.

The distribution of the artefact seems to be affected by which 32-pin electrode set they are on as it doesn't make sense for there to be huge artefact at Cz but none at the immediately adjacent electrodes.

Could anyone give me an explanation about why this might be happening and possible solutions (as simple an explanation a possible would be appreciated!). Thank you.

Coen
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Re: Unsual pattern of artefact

Post by Coen » Fri Jun 24, 2016 11:42 am

Does the varying the included area and orientation of the loops formed by the electrode cables make a difference ? If yes, decrease the pickup of alternating magnetic fields by bundling and twining the electrode cables.

Best regards, Coen (BioSemi)

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