Hi Anja,
> Dear VBM-Experts,
>
> I'm working with anatomical T1-weighted images, scanned with a Siemens
> Symphony 1.5 Tesla MRI scanner (quantum coil system).
> I'm using SPM2 and SPM5b running in MATLAB 5.6.1 and Windows 2000.
> There are some problems doing a VBM analysis:
> Using the SPM2 optimized version there are still parts of dura mater
> parietal in the GM image after the automated extraction and
> segmentation procedure.
> Using SPM5b there are even more parts of dura mater not extracted.
> That's confusing because in the mailing list John Ashburner adviced
> among other things to use SPM5 when extraction problems occure in SPM2
> (20. June 2005).
Well, I cannot really answer your questions but I would say that SPM5
should give better results. Using SPM2 optimized procedure, did you
correct the field inhomogeneity? In SPM5, did you tried separate steps
or run the all analysis in one time? In the later case, SPM5 does not
use the same algorithm(s), i.e. the single pass method adjusts the
parameters of each part (bias, segmentation...) iteratively within the
same algo.
> Now my questions are
> 1. Are there possibilities to improve the results of extraction and
> segmentation within SPM2 or SPM5b? (I've allready tried to multiplcate
> the grey and white matter partitions withe the brain mask. There was
> no improve.) Which parameters can I change to improve the algorithm
> and how does it work?
Maybe you can change your model (number of Gaussian per class) but I not
sure that's a good idea and/or play with the other options (default:
segment - custom)
Hope it helps,
best
- cyril
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