Hi,
On 13 Mar 2009, at 13:36, Alex Fornito wrote:
> Hi all,
> I'm trying to use the -bptf function in fslmaths to temporally
> filter some functional volumes.
> I have two questions:
>
> 1. I just want to check my understanding of how to specify sigma. If
> I want to retain
> frequencies between say .008 and .08 Hz, with a TR of 1.42 s, then
> the correct syntax
> would be:
>
> fslmaths input_4D.nii -bptf 44 4.4 output_4D.nii
>
> (e.g., .08 Hz = 1 cycle every 8.8 vols; sigma = 8.8/2 = 4.4)
Yes, that makes sense. The filter has fairly slow frequency rolloff so
it's fairly tolerant to the exact choice of these parameters.
> 2. When I run the above command on my data, where each 4D file
> contains 840 volumes, I
> get an out of memory error. Can anyone recommend a work around that
> does not involve
> changing the hardware?
See the FSL FAQ entry on big RAM issues; you might get this to work
just by increasing your swap, assuming you have a 64-bit machine.
Alternatively you could try running on a slice at a time by splitting
the data up with fslsplit and the -z option.
Cheers.
>
> Thanks for your help,
> Alex
>
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Stephen M. Smith, Professor of Biomedical Engineering
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