Hi, Emily.
You could use the pencil tool in fslview to make a single voxel mask, then use fslmaths to change the value in that mask to whatever you want (-odt float), and then add it to your original image (or maybe to a copy of the original).
hth,
PaulOn Fri, Mar 30, 2012 at 9:39 AM, Emily Coffey <[log in to unmask]> wrote:Will this tool allow me to do what I need?
http://www.fmrib.ox.ac.uk/fsl/fslview/masking.html