Hi Ting, thanks for your email. The first question is: is FAST giving a
good-looking segmentation? If not, we need to address that first. If it
is, then the bias field correction is probably working correctly!
On Tue, 11 May 2004, Ting wrote:
> I was trying to do the inhomogeneity correction of T1-weighted MRI brain
> data sets. I remove the bones and outer material according to the manual
> labeled data. Then I use FAST to do the inhomogeneity correction. I ploted
> the histogram before and after the inhomogeneity correction. I found that
> in some cases, the ratio of the GM/WM changed much. Before the correction
> the ratio of GM/WM is greater than one, but after the correction the ratio
> is less than one. The average ground truth ratio is around 1.2-1.3.
> Another observation is that the white matter peaks shifted much.
> Therefore, I am confused and wondering if anyone else met the same problem
> before? Is there any parameters to adjust the ratio and peak positions?
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