Hi - yes, FAST gives out a 3D bias image but if you multiply a 4D input
image by this that will act in 4D.
Cheers.
On Fri, 7 Oct 2005, wolf zinke wrote:
> Hi,
>
> Thnk you for the tips, I will try it. The bias correction of Fast will
> only correct the first image of a 4D dataset, am I right? Thus I need
> not split my time series into single 3D files and apply the bias field
> correction on each of them?
>
> Thanks again,
>
> wolf
>
> Martin Kavec wrote:
>
> >Hi Wolf,
> >
> >On Thursday 06 October 2005 21:15, Mark Jenkinson wrote:
> >
> >
> >>Hi,
> >>
> >>Yes, bias field or intensity gradients are a huge problem
> >>for any registration or motion correction utility that uses
> >>voxel intensities to align images. As the intensity is the
> >>only information it has to work with, it is important that
> >>the intensity would be matched well in the aligned images,
> >>but with motion + bias field this is no longer true.
> >>
> >>To fix this problem you can either use bias corrected data
> >>from FAST (or any other method), however, this is not always
> >>
> >>
> >
> >I would encourage you to give a try to bias correction using FAST and after
> >that regular registration. I have great success rate, close to 100%, with
> >this approach and I can tell you that the images, which I work are really
> >problematic: low SNR, geometric distortions due to B0 inhomogeneity, very
> >complicated bias field shape (large surface coil), incomplete brain coverage.
> >
> >Good luck.
> >
> >Martin
> >
> >
>
>
--
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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