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Torben Ellegaard Lund wrote: > In Karl's MRM paper on residual movement artefacts: Magn Reson Med. > 1996 Mar;35(3):346-55. Movement-related effects in fMRI time-series. > http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8699946&query_hl=1 > > they use an expansion of the movement parameters. The expansion > includes in addition to the 6 rigid body movement parameters for a > volume acquired at time t: R(t) it also the movement parameters from > the previous volume R(t-1) and these terms squared: R(t).^2 and > R(t-1).^2, this is 24 extra parameters in your design matrix. In this > way you can model both linear and quadratic term of both the movement, > but also of the velocity of the movement as well as history effects. A combination of these methods would probably be optimal: compute the displacements D for each voxel, and use D(t), D(t-1), D(t).^2, and D(t-1).^2. That would model linear and quadratic displacement terms, as well as velocity and history effects. Computing the displacements as scalars instead of using the 6 parameters, does not introduce 5 `virtual' degrees of freedom for each of those terms, which makes the analysis more powerful. Best wishes, Alle Meije ___________________________________________________________ To help you stay safe and secure online, we've developed the all new Yahoo! Security Centre. http://uk.security.yahoo.com