If you compute DVARS without motion correction, you are going to get a
much higher range of values. While Jonathan may have done some analyses
without motion *regressors* in the preprocessing, I'm pretty sure that
motion *correction* is always included prior to DVARS computation.
Depending on the temporal SNR of your data, a DVARS baseline of 30-40
after motion correction is certainly reasonable.
BTW: You probably want to be specifying a mask as part of your input to
'fsl_motion_outliers'.
cheers,
-MH
--
Michael Harms, Ph.D.
-----------------------------------------------------------
Conte Center for the Neuroscience of Mental Disorders
Washington University School of Medicine
Department of Psychiatry, Box 8134
660 South Euclid Ave. Tel: 314-747-6173
St. Louis, MO 63110 Email: [log in to unmask]
On 2/25/14 11:15 AM, "Angela Favaro" <[log in to unmask]> wrote:
>Hi all,
>I have some problemi in using the script fsl_motion_outliers and I need
>some clarification. I would like to 'scrab' my dataset before using it
>with both melodic and seed-based resting-state analyses.
>
>I tried to use the script with a subject with:
>MCFLIRT Motion correction Mean displacements: absolute=0.08mm,
>relative=0.04mm.
>
>The command I used is:
>fsl_motion_outliers -i file -o file --dvars -nomoco -v
>and I tried to run it in preprocessed data (as described in the paper by
>POwer 2012).
>the output was:
>brainmed = 99.815247 ; maskmean = 0.249414
>Calculating outliers
>Range of metric values: 99.421906 458.086700
>Found 9 outliers over 377.0876780
>Generating EVs
>Found spikes at 89 172 175 192 212 214 215 220 223
>
>I do not understand why the values of DVARS are so high. With unprocessed
>data (and moco allowed) values are lower, but not as expected (I think):
>
>brainmed = 382.000000 ; maskmean = 0.238453
>Calculating outliers
>Range of metric values: 26.647026 39.988392
>Found 5 outliers over 37.0337425
>Generating EVs
>Found spikes at 134 192 203 226 239
>
>What am I doing wrong?
>
>Thank you!
>
>Angela
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