mrtrix3preproc2sh runs the MRtrix3 preprocessing (dwifslpreproc) pipeline on 2 shell data. It uses FSL's topup with the provided inverse phase encoded data. After preprocessing, filed inhomogeneity bias correction with algo:fsl, and brain mask (bet2) is performed (dwibiascorrect fsl). Required inputs are two forward PE diffusion Zipped DICOMs and two corresponding RPE Zipped DICOMs.