>> Dear users,
>>
>> Would some one please tell me that from where can I read the slice
>> acquisition order is ascending (1,2,3...), descending(23,22,21...) or
>> interleaved, (1,3,5... 2,4,6) and the Reference Slice is which slice?
>>
>> I used MRIcro to open the dicomed hdr file (Header - open head), and then
>> click Header - information, however only can see the TR, TE, time and so on
>> there in the notes.
>>
>> Best regards
>> Yiquan
>
> John Ashburner wrote:
>
> From a generative modelling
> perspective, the design matrix, rather than the data, should be adjusted to
> account for different acquisition times (i.e., to maximise the probability of
> the data given the model).
I agree.
As you know, one option (possible now) is to use a more flexible set of
temporal basis functions in the design matrix (eg temporal derivatives
of an assumed HRF) to capture slice-timing differences, but some people
find this confusing - preferring to deal with a single parameter to
represent the size of their evoked response (and it can be statistically
more powerful to estimate a single "latency-invariant" parameter for the
response, eg Calhoun et al, Neuroimage). Also, using parameter estimates
for multiple basis functions as separate regressors in a standard second-
level analysis across subjects, while catering for inter-regional latency
differences, does not cater for inter-subject latency differences.
The other option is to adjust the onset times in the design matrix as a
function of the slice, but doesn't this get problematic after normalisation
(ie nonlinear warping and resampling of original data)? Also, I think
slice-specific design matrices may pose problems (theoretical, but
perhaps not practical) for Random Field Theory?
Rik
--
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Dr Richard Henson
MRC Cognition & Brain Sciences Unit
15 Chaucer Road
Cambridge
CB2 7EF, UK
Office: +44 (0)1223 355 294 x522
Mob: +44 (0)794 1377 345
Fax: +44 (0)1223 359 062
http://www.mrc-cbu.cam.ac.uk/people/rik.henson/personal
-------------------------------------------------------
--
-------------------------------------------------------
Dr Richard Henson
MRC Cognition & Brain Sciences Unit
15 Chaucer Road
Cambridge
CB2 7EF, UK
Office: +44 (0)1223 355 294 x522
Mob: +44 (0)794 1377 345
Fax: +44 (0)1223 359 062
http://www.mrc-cbu.cam.ac.uk/people/rik.henson/personal
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