T1w image is the first argument to BDP on command line. See below for usage. This file should be the bias-field corrected output from BrainSuite in nifti-1 format.
bdp.sh <BFC FILE> [OPTIONAL FLAGS] --nii <NIFTI FILE> --bvec <GRADIENT FILE> --bval <B-VALUE>
More usage details can be found here: http://brainsuite.org/processing/diffusion/pipeline/