There are few, if any, quantitative rules for the amount of motion allowed in an fMRI study.
The 3 mm motion threshold is related to a rule-of-thumb in the community that subjects with maximum motions larger than 2 mm or 3 mm should be excluded from a study. However, this rule-of-thumb discards too many subjects in pediatric and clinical populations.
In practice now, we usually ignore the maximum motion threshold because the large maximum motions are usually from rapid motions, and instead we test for rapid motion mm/TR above a threshold. The rapid motion scans have distortions, realignment errors, and spin history effects, and so they are treated as artifacts. Large slow motions are treated fairly well by a different function in the ArtRepair package. Consequently, we exclude subjects based on too many scans of rapid motion rather than an amount of maximum motion.
Best regards,
Paul
----- Original Message -----
From: "Jen Pokorny" <[log in to unmask]>
To: [log in to unmask]
Sent: Wednesday, October 20, 2010 4:03:13 PM
Subject: [SPM] ArtRepair toolbox
I am currently trying to use the ArtRepair5 toolbox and had a question
regarding setting the motion threshold (mm/TR). I use a cutoff of 3 mm
for overall movement. Does this 3 mm correspond to the motion
threshold mm/TR in the toolbox? Is there a standard guideline on the
parameters one should use for these thresholds?
Thank you for any help!
-Jen
--
----------------------------------------------
Jennifer Pokorny, Ph.D.
Postdoctoral Fellow, Autism Research Training Program
NeuroCognitive Developmental Lab
Center for Mind and Brain, UC-Davis
202 Cousteau Place, Suite 255
Davis, CA 95618
(530) 747- 3808
email: [log in to unmask]
--
Paul K. Mazaika, PhD.
Center for Interdisciplinary Brain Sciences Research
Stanford University School of Medicine
Office: (650)724-6646 Cell: (650)799-8319
CONFIDENTIALITY NOTICE: Information contained in this message and any
attachments is intended only for the addressee(s). If you believe
that you have received this message in error, please notify the
sender immediately by return electronic mail, and please delete it
without further review, disclosure, or copying.
|