Hi Deryk,
one thing to keep in mind about this option is how much impact it really
has, and the answer, in my mind, is "not that much".
If you check figure 3 in John's 1997 NeuroImage paper ("The distribution
of the zooms in x, y, and z required to fit 51 brains to a standard
space.") this tells you that the affine registration is stabilized and
sped up by giving it starting estimates on which affine mapping is
likely to give the best result. I sort of mimicked that figure in a 2002
paper and found that the overall affine scaling does not even correlate
with age in children from 6-18 (although scaling in X did).
Moreover, for example in unified segmentation, this starting estimate is
then iteratively improved and adapted, several times over, so I
personally think it does not make a huge difference, as the starting
estimates for the different options will not be hugely different anyway.
If you want to see if it makes a difference at all, segment 5 datasets
with different affine starting estimates and otherwise identical
options, and check the difference images. If really this has a
substantial influence, then there should be a systematic difference in
the resulting tissue maps.
Best,
Marko
> Dear SPMers
>
> I am preparing a data processing pipeline for VBM analysis of paediatric
> data (7-12 year old boys). I created a custom templates (tissue probability
> maps / priors) and understand that these must be set in the "Tissue
> probability maps" option in either VBM5.1 toolbox or in the Segment routine.
> However, I don't quite understand the impact of affine regularisation. It
> seems the only choices for this option are "ICBM European brains," "Asian
> brains", "average" or none. I have a small group of participants (10
> patients, 10 controls). Affine regularistation to the "average" seems wrong
> given that I've taken the careful step of creating age appropriate tempaltes
> with TOM.
>
> Two questions:
> 1. What is the best option for me?
> 2. Does it even matter if I ultimately end up using the "modulated
> normalised non-linear only" images for my statistical analysis?
>
> Cheers and thanks in advance,
>
> Deryk
>
>
--
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Marko Wilke (Dr.med./M.D.)
[log in to unmask]
Universitäts-Kinderklinik University Children's Hospital
Abt. III (Neuropädiatrie) Dept. III (Pediatric neurology)
Hoppe-Seyler-Str. 1, D - 72076 Tübingen
Tel.: (+49) 07071 29-83416 Fax: (+49) 07071 29-5473
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