MRI data is aquired in K-space (=fourier space), not real space, so
artifacts during acquisition (movement (of eyes!), drift, spikes, etc
etc) can affect entire spatial frequency bands, not just voxels inside
the imaged object.
So your 'activation'outside the imaged object might be due to task
related artifacts, picked up by your regressors of interest. Is not
uncommon, SPM5 by default masks at 0.8 of global image mean and
therefore most people don't notice it.
Good luck,
Bas
neeru K schreef:
> Dear SPMers!
> I am doing fMRI of anesthetized monkeys and I am getting BOLD
> acitvations (analyzed in SPM5) outside the brain (in addition to
> inside the brain), especially in the muscles overlying the skull and
> orbits of eyes and it seems consistent.
> I thought it could be a problem with coregistration but it persistes
> even when I overlay the contrasts onto the mean EPI image....
> Has anybody faced a similar problem in human data and if so what is
> the solution...
> Could there be also a problem in acquisition of the data
>
> Thanks
>
> --
> Niranjan Kambi
> SRF, Neeraj Lab,
> National Brain Research Centre
> Manesar, Gurgaon-122050
> Haryana, INDIA
> Ph:+919818654846
--
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Dr. S.F.W. Neggers
Division of Brain Research
Rudolf Magnus Institute for Neuroscience
Utrecht University Medical Center
Visiting : Heidelberglaan 100, 3584 CX Utrecht
Room B.01.1.03
Mail : Huispost B.01.206, P.O. Box 85500
3508 GA Utrecht, the Netherlands
Tel : +31 (0)30 2509609
Fax : +31 (0)30 2505443
E-mail : [log in to unmask]
Web : http://www.fmri.nl/people/bas.html
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