04 December 2013 15:38
Hello Mark,
The fslmaths call expects input values in sigmas.
For the highpass filter, if you wanted to pass 0.25Hz for a TR of 2, the input sigma to fslmaths would be roughly (1/0.25)/(2TR) = 1
For the lowpass filter, due to its slow roll-off, the input sigma is harder to calculate, a starting point for 0.5Hz and 2 TR might be (1/0.5)/18TR) = 0.1
You will need to use fslmaths for this as the FEAT script does not allow for modifications to the lowpass sigma.
Kind Regards
Matthew
________________________________________
From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Mark Olivetti [[log in to unmask]]
Sent: 02 December 2013 13:08
To: [log in to unmask]
Subject: Re: [FSL] High-Low Pass Filter
Dear Steve,
Thank you for your response, we really appreciate it!
However, could you, or some other members of the FSL group, be so kind and reply to the following questions:
We want to apply a bandpass filter of 0.008-0.10 Hz and our TR is 2.2 sec. Which cutoff values (seconds or sigma’s) should be used to accomplish this? Also, is it possible to apply this bandpass by adjusting the numbers in the design.fsf file (given that lowpass filter option is hidden in the GUI) or should we use fslmaths? Relatedly, is it correct that in the design.fsf file values are in seconds, while the fslmaths command line expects sigma's?
Thanks in advance!
Kind regards,
Mark
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