Dear Lisa,
see below
1) If I divide my entire scanning time series into multiple scan runs,
there will be more than 1 GLMs (I suppose multiple sessions, as in lst
level modelling in SPM, correspond to only multiple GLMs with a mutually
independent set of onsets and durations for each one.) Thus, for each GLM,
the implicit baseline will be different from others. So how can I combine
the contrasts for these GLMs for group level analysis?
I'm not sure about the following:
- you had 1 scanning session (continuous use of the scanner without
switching it off for 40 mins) and you want to divide ts into multiple
sessions (not sure how good it would be)?
or:
- you had real multiple sessions (with breaks in the scanner use)?
I think that in either case you can still come up with a single GLM at the
first level anyway, even if you have separate sets of onsets
Best wishes,
Iwo
On Nov 8 2011, Tingting Wang wrote:
>Dear SPMers,
>
>
>
>I am using SIEMENS trio 3T scanner in our data acquisition. My questions
>are as follows:
>
>
>
>1) If I divide my entire scanning time series into multiple scan runs,
>there will be more than 1 GLMs (I suppose multiple sessions, as in lst
>level modelling in SPM, correspond to only multiple GLMs with a mutually
>independent set of onsets and durations for each one.) Thus, for each GLM,
>the implicit baseline will be different from others. So how can I combine
>the contrasts for these GLMs for group level analysis?
>
>
>
>2) The second question is a more practical one. My entire scanning length
>is approximately 40mins. The motive for dividing scanning session into
>multiple runs is to avoid signal decay problem, after scanning for a long
>time. However, what I am not sure is whether it is necessary in my
>experiment? Has anybody used SIEMENS trio 3T scanner under similar
>circumstance?
>
>
>
>Any advice and comments will be greatly appreciated.
>
>
>
>Best wishes!
>
>
>
> Lisa Wong
>
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