FSL Tutorial 6: Automating FEAT

So now you know enough to run an analysis on your own; Congratulations! However, before you crack open a fresh jar of Nutella to celebrate, be aware that there are other methods that can greatly increase your efficiency, confidence, and libido.

We now turn to a slightly more sophisticated way to run your analyses, that is, through the command line as opposed to the pointing and clicking through the graphical user interface. When I mentioned in the last post that this factors out human error, what I meant was that it eliminates any error due to faulty clicks in the GUI, or fat-finger dialing of any additional parameters. The probability that you would enter everything in by hand the exact same way for every subject is essentially zero. Learning the basics of scripting is essential for any neuroimaging researcher these days, even if it is just to acquire enough familiarity to know what is going on when reading other people's scripts.

Whenever you set up and run an analysis, a file called design.fsf is output into each results directory; this contains everything you specified in the GUI, but in text format. This file can also be generated at any time by using the "Save" option within the FEAT GUI, and conversely, can be loaded using the "Load" option; this will fill in all of the fields as they were when you saved the design.fsf file.

The power of design.fsf comes from its commandline use. Simply type in "feat design.fsf" and it will execute every command inside the design.fsf file, the same as it would if you were to load it into the FEAT GUI and press the Go button.

Honestly, I am surprised that this feature is not showcased more in the FSL documentation; a couple of lines are devoted to its commandline usage in the FEAT basics section of the manual, but really they should emphasize this much more. (There is a good tutorial here about how to swap code within the design.fsf file and execute it with feat.) If you are new to Unix and need to get your feet wet, I suggest going through the following tutorials: One for basic Unix usage, the other for basics of shells scripting. This will be a new language to you, and as with any language, the beginning can be disorienting and overwhelming at times; however, stick with it, and I promise that the fog will begin to clear eventually, and you will discern what exactly it is you need to know when searching the help manuals, and what it is that you can disregard.

For those of you who have enough Unix background to feel comfortable reading scripts, here is something I created for a recent study I analyzed. This is a special case, since there were some runs where the participant was not exposed to a condition; in this case, for that regressor FSL requires you to specify the shape as "All Zeroes", something that we did not cover yet, but something that you should be aware of. The following script will check for whether the timing file is empty or not, and adjust the shape specification accordingly; however, it will also work for studies which have all regressors accounted for and do not have any missing data.

Here is the script, which can also be downloaded here; I apologize that the formatting is a little screwy with the margins:

#!/bin/bash

for run in 01 02 03 04
do
#Loops through all runs and replaces "ChangeMe" with run number

\cp design.fsf tmpDesign.fsf
sed -i -e 's/run01/runChangeMyRun/' tmpDesign.fsf
sed -i -e 's/FSL_01/FSL_ChangeMyRun/' tmpDesign.fsf #Replaces run placeholder with variable "ChangeMyRun"; this will be swapped later with the appropriate run number
iter=1 #Counter for running loops below
while [ $iter -le 11 ] do for timingFile in FSL_"$run"_EmotionRegAM.txt FSL_"$run"_EmotionRegAS.txt FSL_"$run"_EmotionRegNM.txt FSL_"$run"_EmotionRegNS.txt FSL_"$run"_EmotionResp1.txt FSL_"$run"_EmotionResp2.txt FSL_"$run"_EmotionResp3.txt FSL_"$run"_EmotionResp4.txt FSL_"$run"_EmotionResp5.txt FSL_"$run"_Instructions.txt FSL_"$run"_Relax.txt
do
if [ -s ../Timing/$timingFile ] then echo "File found; timing file is "$timingFile
sed -i -e 's/fmri(shape'$iter') 3/fmri(shape'$iter') 3/' tmpDesign.fsf
else
echo "File not found; timing file is " $timingFile sed -i -e 's/fmri(shape'$iter') 3/fmri(shape'$iter') 10/' tmpDesign.fsf fi iter=$(( $iter + 1)) done done \cp tmpDesign.fsf design_$run.fsf #Make a copy for each run
sed -i -e 's/ChangeMyRun/'$run'/' design_$run.fsf #Swap "ChangeMyRun" with run number
\rm *-e #Remove excess schmutz
feat design_\$run.fsf #Run feat for each run
done

Note that a template script is generated by copying a script output by FEAT and replacing "run01" with "runChangeMyRun". ChangeMyRun serves as a placeholder for the run number, being updated on each successive iteration of the loop. The script then executes a while loop, checking each timing file for emptiness, and if it is empty, assigning the appropriate shape in the model. Also note that my timing files, in this example, are located in a directory one level above called "Timing"; this may be different for you, so adjust accordingly if you plan on adapting this script for your purposes.

After that, a new design.fsf is generated for each run, and then executed with feat. If you have more than one subject, then it is a matter of adding another loop on top of this one and going through subjects; with higher-level analyses, replacing single runs of data with .gfeat directories; and so on.

For the beginner, I would recommend opening up a generic design.fsf file with a text editor and using search and replace to update it to the next run. After you get a feel for what is going on, spend some time with Unix and monkey around with the "sed" search and replace tool, until you feel comfortable enough to use it on your design.fsf files; then experiment with loops, and test it on a single subject in a copy directory, so that if something blows up (which it inevitably will on your first go-around), you have a backup.

That is it for the basics of FEAT, and, really, all you need to know for carrying out basic analyses in FSL. Interpreting the results is another matter entirely, but once you have the techniques down, a major part of the drudge work is out of the way, and you can spend more time thinking about and looking at your data; which, really, is what we are trained to do in the first place.

More tutorials will be up soon about the basics of Unix, with an eye on assisting the beginning neuroimaging researcher understand what the hell is going on.