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Hi Loreen, I have been asking myself the same questions some years back :) so perhaps I can be of help here. The short answer is, displacement in "mm" is much more intuitive to most, and is the basis of rejection of datasets in most studies (I think; it certainly was for me). Rotation in "degrees" is somewhat more difficult to quantify, as the resulting translation depends on the distance to the origin around which rotation occurrs. And no, there is no universally accepted answer (there is a rule of thumb that "motion exceeding one voxel size" is too much, but again, this relies on translation only). For the long answer and an approach that condenses all six parameters into one, try searching PubMed (as long as it is still open...) for manuscript ID 22036679; you can also try our website (URL below) and see if you like what you find when you follow the software link :) Hope this helps, Marko Loreen wrote: > Dear SPMers, > > I am aware of conventions for discarding scans with too much residual motion in terms of translation, but can you suggest a reference for a convention on acceptable residual rotation estimates? > > Although the two sets of motion parameters probably go hand in hand for a given subject (i.e. if there is lots of translation, rotation might feature as well), how can I deal with cases where either translation or rotation is problematic? Should I discard as soon as one of the two estimates is deemed too much or might there be a convention where one is viewed less problematic than the other? Intuitively I'd think that both sets of estimates are equally important, but it would be great to hear your views and suggestions. > > Thank you very much! > Loreen > -- ____________________________________________________ PD Dr. med. Marko Wilke Facharzt für Kinder- und Jugendmedizin Leiter, Experimentelle Pädiatrische Neurobildgebung Universitäts-Kinderklinik Abt. III (Neuropädiatrie) Marko Wilke, MD, PhD Pediatrician Head, Experimental Pediatric Neuroimaging University Children's Hospital Dept. III (Pediatric Neurology) Hoppe-Seyler-Str. 1 D - 72076 Tübingen, Germany Tel. +49 7071 29-83416 Fax +49 7071 29-5473 [log in to unmask] http://www.medizin.uni-tuebingen.de/kinder/epn/ ____________________________________________________