Thanks, that is exactly what I wanted to know. Did you quantify how much improvement you got in volume estimation?
Keith
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From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Mark Jenkinson [[log in to unmask]]
Sent: Monday, January 17, 2011 11:17 AM
To: [log in to unmask]
Subject: Re: [FSL] differences between fast3 and fast4
Hi,
The main difference is the partial volume processing.
This now (in FAST4) uses an MRF on the "mixel type" to regularise
the type of mixtures present in voxels. A "mixel" represents what
tissues occur in a mixture (e.g. WM/GM is one mixel, pure WM is
another, GM/CSF is another, etc.). We disallow the triple mixture
WM/GM/CSF by default, and put an MRF on the remaining mixels.
This means that if a voxel might be either a WM/GM mixel or a pure
WM mixel, but is surrounded mainly by pure WM mixels, and the
intensity data is not strong either way, then it will end up being
classified as a pure WM mixel. This has the effect, as you've
noticed, of making the transitions sharper and forcing more voxels
towards "pure" tissue, instead of letting them be 95% one tissue
and 5% another just due to the noise. This model should therefore
give a better segmentation and a better volume estimation - which is
why we replaced the old one, based on our testing.
I hope this is what you were wanting to know.
All the best,
Mark
On 17 Jan 2011, at 15:35, Keith Hulsey wrote:
> A few years back I ran some analysis using SIENAX in FSL version 4.0. The version of FAST which it used was 3.53. I am trying to modify my previous work, but I have found that the segmentation process has changed, as SIENAX now uses FAST version 4.1. Is there a document which explains the changes between fast3 and fast4 other than the conversion table for the program options? Looking at my data, it seems like results using fast4 have a quicker transition from white matter to gray matter at the cerebral cortex, giving fewer partial volume voxels. Would you expect that change given the differences between versions?
>
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