Dear Sabine,
perhaps it has to do with task related movement in the scanner, generating artifacts? Did you try to correlate your task regressors with the 6 movement parameters obtained during rigid body realignment? I wouldn't directly expect such artifacts in the ventricles, but one never nows. What pulse sequence do you use? EPI? Try to incorporate the movement parameters in your design (from your PDF, I guess you didn't?) in order to regress out movement related artifacts (and task related signal in the worst case of correlation between movement and task), and see whether the artifacts are still present.
For me, movement related artifacts are the first suspect when observing activation at unrealistic locations.
Second, I would have a look at your high pass filters, i.e. the cutoff frequency. How long was your experiment, and how long a block? Longer blonk durations result in regressors more likely to correlate with low frequency drifts in the T2* signal.
I hope your subject doesn't suffer from a rare case of dendritic sprouting in the ventricles ;-)
cheers,
Bas
--------------------------------------------
Dr. S.F.W. Neggers
dept. of Psychonomics,Helmholtz Institute
Utrecht University
Heidelberglaan 2
3584 CS, Utrecht, room 17.09
the Netherlands
Tel: (+31) 30 253 4582 Fax: (+31) 30 2534511
E-mail: [log in to unmask]
Web: http://www.fss.uu.nl/psn/pionier
--------------------------------------------
-----Oorspronkelijk bericht-----
Van: SPM (Statistical Parametric Mapping)
[mailto:[log in to unmask]]Namens Tranchant, Sabine (MED, Intern)
Verzonden: dinsdag 13 juli 2004 17:04
Aan: [log in to unmask]
Onderwerp: [SPM] Blobs in ventricle ?
Dear all,
I performed realignment, coregistration, normalisation, smoothing + model
specification and parameter estimation for an fMRI study. During my results
assessment, I realized there was almost no activation except in the
ventricles...
I had no problem with other tasks or subjects so I really wonder what is
wrong. Could anybody help me to understand this result please (see the pdf
file)?
Thank you very much,
Sabine
|