Dear Elkin
Depends on what exactly you did.
When you restricted your analysis space a priori (setting an explicit mask when setting up the analysis) then it is equivalent to both inclusive masking & SVC.
That being said, your results could still differ from what you will get from using inclusive masking & SVC. The reason behind this is, that if you restrict your analysis space a priori, your REML-estimation will only be based on the ROI - not on the whole brain. if the ROI is small, this may lead to quite substantial differences in the estimation (and correction) of non-sphericity.
Best
Simon
2012/5/14 Javier Elkin <[log in to unmask]>:
> Hi Simon,
>
> Since it seems you know about these things, may I ask: If one draws a sphere
> or box in pickatlas and then does an analysis on that zone and the glass
> brain shows activation ONLY in the selected mask, is that a ROI or SVC
> analysis?
>
> cheers!
>
> Javier
>
>>>
>>> Dear Glad
>>>
>>>
>>> Masking is just that: It just doesn't show those voxels that are not in
>>> your mask images (exclusive mask) / just shows voxels within your mask image
>>> (inclusive mask) [look at spm_getSPM at about line 600]. The statistics,
>>> more precisely the correction for multiple comparisons), however, still runs
>>> with respect to the initial analysis space.
>>>
>>> Smal volume correction, in contrast, only corrects for the smaller search
>>> volume and provides correcte p-values for this new analysis space. It
>>> doesn't however, update the image you see in the glass-brain.
>>>
>>> So it is actually a good idea to combine both, mask out voxels outside
>>> the mask (for dispay) and then re-compute your corrected statistics using
>>> SVC for the same mask.
>>>
>>>
>>> Best
>>> Simon
>>>
>>>
>>>
>>> ________________________________________
>>> Von: SPM (Statistical Parametric Mapping) [[log in to unmask]]" im
>>> Auftrag von"Glad Mihai [[log in to unmask]]
>>>
>>> Gesendet: Montag, 14. Mai 2012 10:46
>>> An: [log in to unmask]
>>> Betreff: [SPM] Difference between mask with image and small volume
>>>
>>> Hi,
>>>
>>> can someone explain to me the difference in calculation between masking
>>> (apply masking) a contrast with an image (let's say an anatomical ROI),
>>> and a small volume correction?
>>>
>>> Regards,
>>> Glad
>>>
>>>
>>>
>>> ------------------------------------------------------------------------------------------------
>>>
>>> ------------------------------------------------------------------------------------------------
>>> Forschungszentrum Juelich GmbH
>>> 52425 Juelich
>>> Sitz der Gesellschaft: Juelich
>>> Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498
>>> Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher
>>> Geschaeftsfuehrung: Prof. Dr. Achim Bachem (Vorsitzender),
>>> Karsten Beneke (stellv. Vorsitzender), Prof. Dr.-Ing. Harald Bolt,
>>> Prof. Dr. Sebastian M. Schmidt
>>>
>>> ------------------------------------------------------------------------------------------------
>>>
>>> ------------------------------------------------------------------------------------------------
>>>
>>> Kennen Sie schon unseren neuen Film? http://www.fz-juelich.de/film
>>> Kennen Sie schon unsere app? http://www.fz-juelich.de/app
>>
>>
>> --
>> Glad MIHAI, M.Sc. Biomedical Physics
>> Funktionelle Bildgebung
>> Uni-Klinikum Greifswald
>> Walther-Rathenau-Straße 46
>> 17489 Greifswald
>> www.baltic-imaging-center.de
>
>
--
===================================
Univ.-Prof. Dr. med. Simon B. Eickhoff
Cognitive Neuroscience Group
Institute of Clinical Neuroscience and Medical Psychology
Heinrich-Heine University Düsseldorf
Telefon: +49 211 81 13018
Fax: +49 211 81 13015
eMail: [log in to unmask]
and
Brain Network Modelling Group
Institute for Neuroscience and Medicine (INM-1)
Research Center Jülich
Telefon: +49 2461 61 8609
Fax: +49 2461 61 2820
eMail: [log in to unmask]
|