Movement Threshold


I was wondering whether there is an objective value and threshold I can use to omit participants from group-level analysis based on the amount of movement they made during the task?

My data set contains a healthy control group and a group of patients that are prone to extensive movement. I have pre-processed my data and completed the quality check using the SS_review_driver command. Visually, I know there are 1-2 subjects who display a lot of movement in their anatomical scan and may need to be excluded. I have seen some papers exclude participants who have moved 4mm-6mm, but I am currently looking for an objective threshold to use. I have gone through the AFNI message boards and relevant posts including the “ –help_fields” and understand there are several measures that can be used to indicate noisy subjects, but I am wondering whether there is a specific measure and a threshold II can use?

I have provided some details of my data:

I censored motion at 2mm, included motion into my regression, and censored outliers at 0.1

Average censored motion range= 0.038-0.35
TSNR range= 72-253
Max censored displacement range = 1.03-18.06
Censor fraction= 0-0.19

Thank you very much for your assistance.