unWarpEPI.py and metal artifact

Hey guys-
I have been trying to perform some analysis collected on patients after deep brain stimulator (DBS) placement. We collect data on a Philips Intera 1.5T. There is a “stock” field map sequence that collects gradient reversal data and outputs two EPI volumes - one with AP and one with PA collection. I then collect a resting state sequence (in AP) as well. When I process the data with afni_proc.py the results are not terrible. I used ANATICOR instead of WM or CSF regressors. The DBS metal artifact seems tolerable. Nevertheless, I would like to use unWarpEPI.py to correct any susceptibility artifact. The output is more distorted than the original EPI. Here are the calls that I am using to process my data:

unWarpEPI.py -f EPI_PA_field.nii -r EPI_AP_field.nii -d EPI_resting
-a T1_mprage.nii --giant_move

afni_proc.py -subj_id ${PTDIR}
-dsets ${DATADIR}/EPI_resting.nii
-copy_anat ${DATADIR}/T1_mprage.nii
-blocks despike tshift align tlrc volreg blur mask regress
-tcat_remove_first_trs 0
-volreg_align_to MIN_OUTLIER
-volreg_align_e2a –tlrc_NL_warp
-align_opts_aea -cost lpc+ZZ -giant_move
-mask_apply epi
-blur_size 6.0
-regress_censor_motion 0.4
-regress_bandpass 0.01 0.1
-regress_apply_mot_types demean deriv
-regress_run_clustsim no


We haven’t had exactly this combination of data before. Just as a guess, you may have to bias correct the data beforehand with 3dUnifize. If you would like, you can upload some data to me, and I’ll try to take a look. I’ll PM you with some instructions if you are amenable.