John, Veda,
I would like to join in on this discussion as I have done that, but was
not sure it is a good idea... the point is, if I correct for
inhomogeneities in an EPI image, how do I do that - do I estimate one
bias field from, say, the mean EPI, and then apply that correction to
all EPIs in this series (+/- individual rotations?), or do I estimate it
from each EPI independently? Personally, I was scared of option 1
because of between-timepoint motion, and of option 2 as then the
correction may induce signal differences between timepoints that
exceed/dominate the resulting statistics. I have played with either
option some years ago and was rather surprised by the effects in the
resulting SPMs in some sample series, so I dropped it, but I have not
looked at it in a systematic fashion and would be interested to hear
what others are saying.
Cheers,
Marko
John Ashburner wrote:
> You could try bias correcting via one of the segmentation routines in SPM.
>
> Best regards,
> -John
>
>
> On 25 June 2012 10:00, SUBSCRIBE SPM Veda <[log in to unmask]> wrote:
>> Dear SPM experts,
>>
>> I spotted a problem of magnetic field inhomogeneity in my original EPI data. That is, the images were brighter in the frontal region than in other regions. I wonder whether there are any functions implemented in SPM can correct for the magnetic field inhomogeneity. If so, could anyone please tell me what the function is and where I find it? If not, please also tell me whether there is other software could support to do the correction. Thanks!
>>
>> Sincerely,
>> Veda
>
--
____________________________________________________
PD Dr. med. Marko Wilke
Facharzt für Kinder- und Jugendmedizin
Leiter, Experimentelle Pädiatrische Neurobildgebung
Universitäts-Kinderklinik
Abt. III (Neuropädiatrie)
Marko Wilke, MD, PhD
Pediatrician
Head, Experimental Pediatric Neuroimaging
University Children's Hospital
Dept. III (Pediatric Neurology)
Hoppe-Seyler-Str. 1
D - 72076 Tübingen, Germany
Tel. +49 7071 29-83416
Fax +49 7071 29-5473
[log in to unmask]
http://www.medizin.uni-tuebingen.de/kinder/epn/
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