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NEUROMEG  January 2014

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Subject:

Re: blink/cardiac artifact removal on single runs or on all dataset?

From:

Marco Buiatti <[log in to unmask]>

Reply-To:

Marco Buiatti <[log in to unmask]>

Date:

Fri, 24 Jan 2014 14:05:13 +0100

Content-Type:

text/plain

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text/plain (100 lines)

Dear all,

I'd be happy to have some feedback on my question, which I think is
quite a general issue. If however you think it's trivial, I'd be happy
to know the obvious solution :-)

Thanks,

Best,

Marco

On 17 January 2014 15:47, Marco Buiatti <[log in to unmask]> wrote:
> Dear Neuromag users,
>
> I have a question concerning what is the best strategy to compute SSP
> projectors for blink/cardiac artifact removal in Neuromag data.
>
> Typical datasets from my lab contain 4 to 8 separate runs from each
> subjects, and co-registration across runs is typically computed with
> Maxfilter (Maxmove), based on the head position measurement performed
> at the beginning of each run.
>
> In principle, since co-registration has already been done, it should
> make sense to compute SSPs for all runs together. However, from my
> experience, results are not always as good as by computing and
> applying SSPs to each run separately.
>
> To test this, I have compared the two approaches on one of my datasets:
> 1) Local: Compute SSPs for both blinks and cardiac artifacts
> separately on each run (here the first run of my dataset)
> 2) Global: Compute SSPs for both blinks and cardiac artifacts on all
> runs together.
>
> My dataset consists in 8 runs of 6 minutes each, already co-registered
> by MaxMove.
>
> I did this test by using Brainstorm (actually, I have posted a similar
> message on the Brainstorm forum a few weeks ago, but I did not get any
> feedback from the Neuromag users).
>
> Here I attach:
> * The blink and cardiac artifact for MAG (top row) and GRAD (bottom
> row, topography is the norm of the grads), first run.
> * The SSP projectors for MAG and GRAD for blinks (top row) and cardiac
> (bottom row) for approach 1) (local) and 2) (global). They look very
> similar, though blink topographies are more localized around the eyes
> for the 'local' approach, and cardiac topographies look also slightly
> cleaner.
> * Comparison of residual blink for local (left side) vs global (right
> side) approach.
> * Comparison of residual cardiac for local (left side) vs global
> (right side) approach.
>
> As you see, though most of the artifact is removed with both
> approaches (note the change in scale of the amplitude), the local
> approach is more successful.
> Of course, it is just an example, I cannot generalize.
>
> Is this due to an inefficient co-registration, or is it possible that
> blinks/cardiac artifacts change during the recordings?
>
> What is your typical procedure?
>
> Thanks in advance for your feedback,
>
> Best,
>
> Marco
>
> --
> Marco Buiatti, PhD
>
> CEA/DSV/I2BM / NeuroSpin
> INSERM U992 - Cognitive Neuroimaging Unit
> Bāt 145 - Point Courrier 156
> Gif sur Yvette F-91191  FRANCE
> Ph:  +33(0)169.08.65.21
> Fax: +33(0)169.08.79.73
> E-mail: [log in to unmask]
> http://www.unicog.org/pm/pmwiki.php/Main/MarcoBuiatti
>
> ***********************************************



-- 
Marco Buiatti, PhD

CEA/DSV/I2BM / NeuroSpin
INSERM U992 - Cognitive Neuroimaging Unit
Bāt 145 - Point Courrier 156
Gif sur Yvette F-91191  FRANCE
Ph:  +33(0)169.08.65.21
Fax: +33(0)169.08.79.73
E-mail: [log in to unmask]
http://www.unicog.org/pm/pmwiki.php/Main/MarcoBuiatti

***********************************************

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