Hi, I've encountered a strange problem: Using probtrackx multiple masks to look at the fdt_paths between two masks... I get sensible results using FSL 4.1.4. However my colleague running the same exact data on his machine was getting an empty fdt_paths file. Turns out he is running 4.1.5. I installed 4.1.5 on my machine, and was able to replicate his empty fdt_paths file result. When I switch back to 4.1.4, I get the expected good result. This only seems to happen with multiple masks. A single mask tracking seems to work fine in both versions. We're both using OS X 10.5. thx mark