Hi Katrin and Julia,
When you use the estimation of the parameters you are trying to reduce
any signal that is correlated with the detected movement, i.e. you are
looking for movement that, despite the movement correction, still exists
in your study. This can be very useful for studies in which there is a
lot of movement.
I found this mail interesting:
http://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind02&L=SPM&D=0&I=-3&P=188062
Best,
Juan
Katrin Scharpf wrote:
> Dear SPM,
>
> once again a question concerning the use of the realignment parameters
> as regressors in the design matrix:
>
> Some people first use these parameters to reduce differences between
> certain volumes and the reference volume during preprocessing and then
> include them again in the design matrix. But don´t you apply these
> regressors on data that are changed according to these regressors in
> this case?
>
> In other words: In the first step you estimate parameters that explain
> a certain amount of variability in the data. Then you change the data
> according to these parameters (reslicing the data). If you now include
> the movement parameters in the design matrix they explain variance in
> data that does not exist like that anymore.
>
> confused greetings,
> Katrin and Julia
>
>
--
________________________________________________________
Juan J. Lull Noguera - jualulno_at_upvnet.upv.es
[MI - Medical Imaging Area]
BET - Bioengineering, Electronics and Telemedicine Group
UPV - Politechnical University of Valencia - Spain
________________________________________________________
[IM - Área de Imagen]
BET - Grupo de Bioingeniería, Electrónica y Telemedicina
UPV - Universidad Politécnica de Valencia
________________________________________________________
"My definition of an expert in any field is a person who
knows enough about what's really going on to be scared."
- PJ Plauger
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