Hi!
Thanks, but wouldn't this filter out *everything else*, leaving only the frequencies in the 0.09-0.11 Hz as the output?
Annelene
>-----Original Message-----
>From: FSL - FMRIB's Software Library <[log in to unmask]> On Behalf Of
>paul mccarthy
>Sent: Sunday, December 30, 2018 6:54 PM
>To: [log in to unmask]
>Subject: Re: [FSL] How to filter out frequency identified in 'power spectra 3'
>window in FSLeyes
>
>Hi Annelene,
>
>The units along the X-axis are the signal frequency. You can use the -bptf
>option to fslmaths to apply a band-pass filter. You need to specify the high-
>and low-pass frequencies as sigma values in volumes.
>You can convert from frequency to sigma (in volumes) using the following
>formula:
>
>sigma_vols = 1.0 / (2.0 * freq * TR)
>
>So if, for example, your data has a TR of 2 seconds, and you want to filter out
>frequences in the range 0.09-0.11Hz, you would use the following sigma
>values:
>
>sigma_lp = 1.0 / (2.0 * 0.09 * 2.0) = 2.7778 sigma_hp = 1.0 / (2.0 * 0.11 * 2.0) =
>2.2727
>
>i.e.
> fslmaths <input> -bptf 2.2727 2.7778 <output>
>
>However, the low-pass filter has a very slow roll-off, so you may need to
>experiment a little with the low-pass sigma to get the results you want. Also
>note that you may wish to de-/re-mean your data before/after applying the
>filter.
>
>See these posts for more information:
> - https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=fsl;9ffadc97.1109
> - https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=FSL;36bcf0ce.1709
> - https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=FSL;c65efaab.1312
>
>Cheers,
>
>Paul
>
>
>
>
>
>
>On 30/12/2018, Annelene Dahl <[log in to unmask]> wrote:
>> Hi!
>>
>> I have discovered an artifact that keeps appearing in the resting
>> state raw data in all my subjects, and using FSL eyes, it seems from
>> the 'Power Spectra 3' window that it has a very specific frequency,
>> which extends over multiple components seen with ICA. I am attaching a
>> screenshot of the FSL/Melodic view to make it clearer.
>>
>> I would like to try to filter out this frequency, and in doing so I
>> have two
>> questions:
>>
>> 1) What are the units on the x-axis in 'Power Spectra 3' window - Hz? MHz?
>> 2) How would one go about removing a specific band of frequencies? Is
>> there a fslmaths command to remove a particular frequency in the middle?
>>
>> Thanks for your help, and happy new year!
>>
>> Annelene
>>
>>
>>
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