Hello,

In this case, two combinations of inputs that would work are 

studydir = '/Applications/Mac64/'; % root folder for data from all study subjects
subject_list = {'dki_example_data_nifti'}; % cell array of subject sub-folders within the root folder studydir
preprocess_options_fn_nii='4d.nii';

OR

studydir = '/Applications/Mac64/dki_example_data_nifti''; % root folder for data from all study subjects
subject_list = {''}; % cell array of subject sub-folders within the root folder studydir
preprocess_options_fn_nii='4d.nii';

This is because DKE will concatenate these three variables to create a full path to your nii images. This was intended for convenience. 

If you wanted to run DKE on multiple datasets, you put the following in your parameters file:

studydir = '/Applications/Mac64/'; % root folder for data from all study subjects
subject_list = {'dki_example_data_nifti','dki_example_data_subject2'}; % cell array of subject sub-folders within the root folder studydir
preprocess_options_fn_nii='4d.nii';

This would require the files '/Applications/Mac64/dki_example_data_nifti/4d.nii' and '/Applications/Mac64/dki_example_data_subject2/4d.nii' both to exist.

-Andrew

P.S. You DON'T have to worry about getting the slashes right where path segments from multiple variables are joined e.g. /Applications/Mac64/ and /Applications/Mac64 would both work for "study_dir". All other slashes, however, matter.