fslmerge

#!/bin/sh

# Usage: fslmerge <-x/y/z/t/a/tr> <output> <file1 file2 .......> [tr value in seconds] 
# -t : concatenate images in time 
# -x : concatenate images in the x direction 
# -y : concatenate images in the y direction 
# -z : concatenate images in the z direction 
# -a : auto-choose: single slices -> volume, volumes -> 4D (time series) 
# -tr : concatenate images in time and set the output image tr (repetition time)
# to the final option value (tr is sometimes stripped by another program) 
# Note that the output file comes before the files to merge!

fslmerge -t img1 img2 img1and2_concatenated