Hello Leighton, the -t option ( like all other options in fslmerge ) concatenates images in the order they are listed on the command line. No image meta-data is used to alter this order. Kind Regards Matthew > Hi Paul, > My 25 images are not an fMRI sequence, but were aquired singly over a 12 month period. > I was concerned that the fslmerge 't' concatenation might access the dates/times and thereby order the images differently to the order in the fslmerge command line. > By the way - how does one get the previous messages in a thread to appear in a reply? > Thanks Leighton >