Dear SPMers,
can anyone tell me the approximate time for running a permuted t-test
with 10 000 permutations with SnPM or XBAM? The dataset consists of 80
volumes with 64 x 64 x 30 voxels.
/Anders
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Anders Eklund
Phd student
Medical Informatics, Department of Biomedical Engineering
CMIV, Center for Medical Image Science and Visualisation
Tel: +46 73 6003790 mail: [log in to unmask]
Fax: +46 13 101902 web: http://www.wanderineconsulting.com/
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Michel Thiebaut de Schotten skrev 2010-08-14 12:58:
> Dear JL,
>
> Many voxels in FA do not have a gaussian distribution at the group level. Smoothing "force" or "help" having a more gaussian distribution but it is not perfect (I recommend Jones et al. NeuroImage (2005) vol. 26 (2) pp. 546-54). Therefore, it is better to use non parametric statistics like snpm (Nichols and Holmes. Human Brain Mapping (2002) vol. 15 (1) pp. 1-25), XBAM (http://www.brainmap.co.uk/xbam.htm) or Tract based statistics from FSL (Smith et al. NeuroImage (2006)vol. 31 (4) pp. 1487-505).
>
> Smoothing also help to reduce the inter-individual variability as no brain normalization algorithm is perfect. Hence it is recommended to use a smoothing according to the level of details you want to interpret (ie: if you smooth at 8*8*8, theoretically you can only make inference on significant cluster>512 voxels, 4*4*4 --> > 64 voxels).
>
> hope it helps !
> cheers,
>
> michel
>
> On Aug 14, 2010, at 9:04 AM, Jung L Hsu wrote:
>
>
>> Dear SPM experts,
>> I wounder if I can use spm two group t-test statistic inference in such a way. I perform DTI analysis and I have 2 groups' FA images. I try to compare their difference. If I did not perform spatial smoothing, could I still use spm statistic inference ? Should I still need to perform spatial smoothing in data image even I use snpm analysis? than is, no smoothing data can not enter into snpm analysi ? thanks for suggestion
>> best
>> JL
>>
> Michel Thiebaut de Schotten, PhD
> NATBRAINLAB
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