Christian,
Hello. Thank you for the response. What you say makes perfect sense. So I
wont do it! But how does the removal of say 5 components affect the residual
noise and dof? Granted it would not be as bad as removing 60 components but
it will have some effect I suppose.
All the best,
Jason.
On Thu, 23 Nov 2006 11:21:48 +0000, Christian Beckmann
<[log in to unmask]> wrote:
>Hi
>
>melodic represents the 20 'interesting' components as the set of IC
>maps and associated time courses. You could load these two things
>into e.g. matlab and re-calculate the their outer product to get a 4D
>file which only contains the 20 components. Note that (i) you'd need
>to run melodic with the --Ostats folder and then use melodic_oIC
>together with melodic_mix or melodic_pca together with
>melodic_dewhite (ii) this new outer product will have the time-course
>mean removed at every voxel.
>I'm not sure what you're setting out to do but just in case you're
>planning to feed this 4D file into FEAT: the stats that feat then
>spits out will _not_ be valid, i.e. t/z/p values become quite
>meaningless, given that in the process of throwing out 60 of the
>directions you're messing with the residual noise and the degrees-of-
>freedom...
>
>hope this helps
>christian
>
>
>
>On 22 Nov 2006, at 16:25, Jason Steffener wrote:
>
>> Hello.
>> I am looking into using Melodic on my data. Can it be
>> used to just remove the "small" components and keep
>> just the number of components it estimates from the
>> data?
>> If I have 80 time points the maximum number of
>> components it can find is 80. If Melodic finds that 20
>> of these are of interest can I just keep these 20 and
>> remove the remaining 60 from my data?
>>
>> Thank you,
>> Jason.
>
>--
> Christian F. Beckmann
> Oxford University Centre for Functional
> Magnetic Resonance Imaging of the Brain,
> John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
> Email: [log in to unmask] - http://www.fmrib.ox.ac.uk/~beckmann/
> Phone: +44(0)1865 222551 Fax: +44(0)1865 222717
>=========================================================================
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