Thanks for the paper. We do have a composite measure of motion from Artifact Reduction Toolbox, and we screened participants scans based on composite measures rather than separately by translational/rotational measures. But I was thinking to report some stats separately for each motion parameter to show the average and age effects.
Perhaps instead I should report the stats for the composite measure? It is just I feel that the values of composite measures are less interpretable.
Are there some guidelines/rule of thumb on how to interpret the magnitude of these composite measures?
----- Original Message -----
From: "Marko Wilke" <[log in to unmask]>
To: "Lingfei Tang" <[log in to unmask]>, [log in to unmask]
Sent: Monday, June 8, 2015 11:48:28 AM
Subject: Re: [SPM] Motion parameter summary
> When summarizing the motion parameters, I am wondering how I should average. Say I have 3 runs, each run having a rp file, should I average within per run and then average across 3 runs.
I am not completely sure what you mean, and why you want to do it... but
assuming you want to describe the amount of motion per subject, per
session, I would like to suggest to not only rely on these parameters to
assess subject motion. I humbly suggest you take a look at a recent
concoction of mine at http://www.ncbi.nlm.nih.gov/pubmed/25333359 for
the reasons why I think this is not an excellent idea.
I may have misunderstood your question, though, as averaging motion
across sessions does not seem to make much sense to me (each session is
either acceptable, or not - a bad one will not outweigh a good one, or
> The first line of the rp files are always all 0s and each line is against the first scan. When averaging, should I do a subtraction to get the scan-to-scan movement, or should I just average from 2 to last line within each rp file?
The first line is zeros as motion is "corrected for" by realigning all
subsequent scans to the first one. Therefore, by definition the first
scan did not move (this is also true if you select "register to mean",
as explained at
PD Dr. med. Marko Wilke
Facharzt für Kinder- und Jugendmedizin
Leiter, Experimentelle Pädiatrische Neurobildgebung
Abt. III (Neuropädiatrie)
Marko Wilke, MD, PhD
Head, Experimental Pediatric Neuroimaging
University Children's Hospital
Dept. III (Pediatric Neurology)
D - 72076 Tübingen, Germany
Tel. +49 7071 29-83416
Fax +49 7071 29-5473
[log in to unmask]