In the future please use tickmarks (or the </> button in the text editor) to format your code/terminal outputs better for readability. You can see I edited your post for you this time.
You did not specify an input image. That is, your -i argument is not defined.
It looks like it also requires a -m argument. Also, the -e argument should be referring to a brain extraction template which isn’t typically just a brain mask. From the documentation:
❯ antsBrainExtraction.sh -h
antsBrainExtraction.sh performs template-based brain extraction.
Usage:
antsBrainExtraction.sh -d imageDimension
-a anatomicalImage
-e brainExtractionTemplate
-m brainExtractionProbabilityMask
<OPT_ARGS>
-o outputPrefix
Example:
bash /Applications/ants-2.5.3/bin/antsBrainExtraction.sh -d 3 -a t1.nii.gz -e brainWithSkullTemplate.nii.gz -m brainPrior.nii.gz -o output
Required arguments:
-d: Image dimension 2 or 3 for 2- or 3-dimensional image (default = 3)
-a: Anatomical image Structural image, typically T1. If more than one
anatomical image is specified, subsequently specified
images are used during the segmentation process. However,
only the first image is used in the registration of priors.
Our suggestion would be to specify the T1 as the first image.
-e: Brain extraction template Anatomical template.
-m: Brain extraction probability mask Brain probability mask, with intensity range 1 (definitely brain)
to 0 (definitely background).
-o: Output prefix Output directory + file prefix.