BUG: Estimated output baseline image incorrect when using "DWI Volume Masking"
Created by: orbe77
Fixes bug reported on Mantis with ID 0003855 on 2014-12-17.
The updated line calculates the magnitude of each of the gradients, and determines that an image is "baseline" if the magnitude is smaller than a threshold. The use of abs() on double values caused the magnitude to always be 0, and therefore all images were considered as "baseline" and included in the average computed by the filter and presented as "Output baseline volume" to the user.