Dear Alfonso,

I have been working on preprocessing resting-state fMRI data with field maps to correct AP-PA distortion. I have 4 runs of rsfMRI images (two AP rsfMRI images and two PA rsfMRI images) and 2 runs of field map images (one AP field map and one PA field map) for one participant. My field map output from the Siemens scanner consists of just one NIfTI file without separate phase/magnitude images.

Following previous posts in this forum, I used FSL topup to create an estimated field map volume (in Hz units) from the AP and PA field map images. This process resulted in a single field map image.

I then entered that field map image into CONN as a “fmap” secondary dataset (same fmap for 4 sessions of resting-state fMRI: 2 AP and 2 PA) and used the preprocessing pipeline for volume-based analysis when field maps are available.

However, during preprocessing in CONN, I noticed a suspicious message in the history window:

“Preparing functional Creation of voxel-displacement maps (VDM) for Susceptibility Distortion Correction
units of FieldMap /Users/data/…/myfieldmap.nii not found, assuming Hz
Creating vdm file for subject 1 session 1...”

Did I make any mistakes? How can I get CONN to recognize the units of my field map? 
I would sincerely appreciate your help.

Thanks,
Hyeonmin