I've read many a paper in which realignment parameters *aren't* used.
Johnstone et al 2006 HBM investigates using/not using them in blocked
and event-related designs.
Regardless, just because "everybody's doing it" wouldn't make it right.
What matters is what's right for your data. If the motion is correlated
w/ your stimulus (and it very clearly is), then stimulus-related effects
will be removed and you won't see anything, and it won't get published
anyway.
Gandolla Marta wrote:
> well, sorry for bothering you all again...
> my concern is that quite everyone in literature uses realignment
> parameters as covariats of no interest... do you think it is ok not to
> use them?
> thanks for the help
> marta
>
> 2010/8/26 Chris Watson <[log in to unmask]
> <mailto:[log in to unmask]>>
>
> Don't include motion parameters as regressors.
>
> I'm sure you already do this, but I've seen that it's good to have
> a practice session outside of the scanner to see how much they
> move when doing the task. Then you can coach them into trying to
> move their body less. Also, putting some pillows under their
> knees, so their feet are elevated, helps quite a bit. And of
> course vacuum bags, tape across the forehead, etc.
>
> Gandolla Marta wrote:
>
> Hi Chris and list,
> so, what do you suggest?
>
> 2010/8/26 Chris Watson
> <[log in to unmask]
> <mailto:[log in to unmask]>
> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>>>
>
> I think that for something as simple as ankle dorsiflexion,
> if the
> results are in a plausible location, you can believe them. The
> motion really isn't that bad. It's hard to keep a patient still
> when doing foot movements, so there will probably always be
> stimulus-correlated motion, and if you include the motion
> parameters as regressors (as you have seen already), it'll
> get rid
> of any true activation.
>
> Gandolla Marta wrote:
>
> Hi Chris and everyone else!!
> indeed, we are looking at right ankle dorsiflexion
> and yes,
> I definitively agree that the activation seems to be quite
> posterior.
> the graph I posted has on x axis the number of scan
> (TR=3secs,
> 5 minutes of acquisition). on the y axis there are mm for
> blue, green and d line, and degrees for yellow, cyan and
> magenta line. I superimposed all the realignemnt parameters
> along with the block design to search for the eventual
> correlation. I attached in any case te SPM output of
> realignment.
>
> all my best
> marta
> 2010/8/26 Chris Watson
> <[log in to unmask]
> <mailto:[log in to unmask]>
> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>>
> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>
> <mailto:[log in to unmask]
> <mailto:[log in to unmask]>>>>
>
>
> Is it right ankle dorsiflexion that you're looking at?
> It looks pretty posterior to the motor strip; what
> does it look
> like overlaid on a structural?
> What's the scale (units) of the graph you posted?
> Can you
> post the
> output of SPM's realignment?
>
>
> Gandolla Marta wrote:
>
> Hi everyone,
> I attached a pdf file instead of a docx of
> the previous
> e-mail. sorry for the inconvenience!!
> I'd need some help about realignment parameters
> effect that
> seems to be huge in the acquisition I will now
> describe.
> We have a 30 secs block design, starting from
> rest. The
> patient is performing active ankle dorsiflexion
> during
> on blocks.
> We did the following preprocessing steps:
> - realignment
> - coreg
> - normalize
> - smooth (6mm)
> then we implemented the GLM with a 8 columns
> design matrix
> (1-condition with the 30 secs block design, 2-7-
> realign
> param, 8- baseline) and we found zero activation
> (p<0.01 FWE
> corrected).
> we then chacked with the 2 columns design matrix
> (1-condition
> with the 30 secs block design, 2- baseline) and
> we found a
> quite important activation (fig.1). should we
> trust this
> activation? the realignemnt param plot along
> with the block
> design protocol is shown in fig.2. is it
> possible that all
> this effect depends on the correlation between the
> realignment
> parameters and the condition column in the
> design matrix?
> should trust only the design with the realignement
> parameters
> as covariats of no interest? we are thinking in this
> case why
> we don't see any activation... do we miss something?
> thanks for your help
> best regards
> marta
>
>
>
>
|