Apply suggestions from code review

Co-Authored-By: Chris Markiewicz <effigies@gmail.com>

Author: josephmje

nipype/interfaces/fsl/epi.py

@@ -565,8 +565,9 @@ class EddyInputSpec(FSLCommandInputSpec):
     in_topup_movpar = File(
         exists=True,
         requires=['in_topup_fieldcoef'],
-        desc='Topup results file containing the movement parameters')
+        desc='Topup results file containing the movement parameters (movpar.txt)')
     field = File(
+        exists=True,
         argstr='--field=%s',
         desc=('Non-topup derived fieldmap scaled in Hz'))
     field_mat = File(
@@ -676,15 +677,15 @@ class EddyInputSpec(FSLCommandInputSpec):
         desc='Consider outliers among sums-of-squared differences if set',
         requires=['repol'],
         min_ver='5.0.10')
-    mb = traits.Int(
+    multiband_factor = traits.Int(
         argstr='--mb=%s',
         desc='Multi-band factor',
         min_ver='5.0.10')
-    mb_offs = traits.Enum(
+    multiband_offset = traits.Enum(
         0,
         1,
         -1,
-        argstr='--mb_offs=%s',
+        argstr='--mb_offs=%d',
         desc=('Multi-band offset (-1 if bottom slice removed, 1 if '
               'top slice removed'),
         requires=['mb'],
@@ -695,7 +696,7 @@ class EddyInputSpec(FSLCommandInputSpec):
         desc='Order of slice-to-vol movement model',
         requires=['use_cuda'],
         min_ver='5.0.11')
-    s2v_niter = traits.Int(
+    slice2vol_iterations = traits.Int(
         argstr='--s2v_niter=%s',
         desc='Number of iterations for slice-to-vol',
         requires=['mporder'],