[FIX] #2435 Error creating gradients in DTIRecon

The bvecs file was read assuming that directions followed YZX order, which created a gradients_matrix.txt with swapped directions. The new order is XYZ.

Author: mmromero

nipype/interfaces/diffusion_toolkit/dti.py

@@ -103,15 +103,15 @@ def _create_gradient_matrix(self, bvecs_file, bvals_file):
         with open(bvals_file) as fbvals:
             bvals = [val for val in re.split('\s+', fbvals.readline().strip())]
         with open(bvecs_file) as fbvecs:
-            bvecs_y = [
+            bvecs_x = [
                 val for val in re.split('\s+',
                                         fbvecs.readline().strip())
             ]
-            bvecs_z = [
+            bvecs_y = [
                 val for val in re.split('\s+',
                                         fbvecs.readline().strip())
             ]
-            bvecs_x = [
+            bvecs_z = [
                 val for val in re.split('\s+',
                                         fbvecs.readline().strip())
             ]