Max Censored Displacement

AFNI Message Board
1

Hi AFNI team,

I am analyzing database resting state images with one functional run each. I noticed in my output that some participants have a large max censored displacement ranging from 1-3. How is this value calculated?

Thank you,
Jenna

2

3dvolreg’s help has some information.

-maxdisp = Print the maximum displacement (in mm) for brain voxels.
(‘Brain’ here is defined by the same algorithm as used
in the command ‘3dAutomask -clfrac 0.33’; the displacement
for each non-interior point in this mask is calculated.)
If ‘-verbose’ is given, the max displacement will be
printed to the screen for each sub-brick; otherwise,
just the overall maximum displacement will get output.
** This displacement is relative to the base volume.

3

Hi Jenna,

You might be referring to the max censored displacement output at the end of an afni_proc.py script. In that case, maximum displacement between volreg parameters (Euclidean distance of first differences) among all pairs of volumes (not just consecutive). It can easily get up between 5 and 10 mm (approximate mm).

Just for demonstration purposes, we were dropping subjects for whom that value was >= 8.

See AFNI_demos/AFNI_pamenc/AFNI_02_pamenc/global_process_outline.txt, and search for that “max censored displacement” string.

  • rick