Maximum motion displacement does not change with certain Euclidean norm cut-offs

Hi all,

I’m having some issues with determining maximum motion displacement before and after censoring using 1d_tool’s -show_max_displace option. For example, with one of my subjects, the maximum motion displacement value only changes after censoring if I set the Euclidean norm cut-off (-censor_motion) at 0.7 or lower. If I use 0.8 or higher, the maximum motion displacement value does not change with censoring, even if there is a TR omitted for excess motion in the censor file.

Why is this? I would think the maximum motion displacement would change, regardless of the cut-off, as long as there is at least one TR that is being censored. The maximum motion displacement for the next highest TR would be reported instead. I would suspect the TRs listed in the censor file are not being censored in the dfile, but then why would it work at some cut-off values and not others? That, and the script matches the example in the help for 1d_tool. I’ve copy/pasted the relevant script below:

#Determine maximum motion displacement (mm) before censoring -infile dfile.breathhold.E.1D -show_max_displace

#Create a file that will allow us to censor TRs where the Euclidean norm of the motion parameter derivative is more than 0.3 (~mm/degrees). This is a good value for healthy adults, but I may need to increase this cut-off depending on the number of TRs that are being censored. -infile dfile.breathhold.E.1D -set_nruns 1 -set_tr 4 -censor_motion 0.8 motion.105.breathhold.E

#Display a list of the TRs censored based on motion, and the total number of censored TRs. -infile motion.105.breathhold.E_censor.1D -show_censor_count -show_trs_censored comma

#Determine maximum motion displacement with censoring -infile dfile.breathhold.E.1D -show_max_displace -censor_infile motion.105.breathhold.E_censor.1D


The maximum motion displacement is between ANY pair
of volumes, not just each volume against the motion
base. So the max displacement is not just equal to
maximum enorm (though by the triangle inequality, it
is <= twice that).

If a censor change does not remove either of the limiting
volumes, then it will not affect the value.

  • rick