Hi,
There was no single measure that we used, and our assessment was
based largely on the segmentation quality, but we also looked at how
it performed in VBM and SIENA. As it seemed to do well in various
measures, or at least not obviously worse - as sometimes the change
was minor - and it had a theoretical advantage of dealing with the
partial volume in a more rigorous way that it did in the previous version
of FAST, we took the decision to change over.
Sorry I don't have a simpler answer, but it wasn't a simple assessment.
All the best,
Mark
On 17 Jan 2011, at 17:21, Keith Hulsey wrote:
> Thanks, that is exactly what I wanted to know. Did you quantify how much improvement you got in volume estimation?
> Keith
> ________________________________________
> 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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