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Hi Jerome, yes, SPM will probably slower on 4D files than on 3D files. Also it will be slower on .nii files than on .hdr/.img pairs. The reason is, that for combined header and data files (as in 3D .nii and 4D cases) SPM needs something like random-write-access to your file to store small bits of information. This is more expensive in terms of I/O time (especially on large disks/RAID systems/network file storage) than storing 3D data with separate .hdr/.img files. However, storing one large file is more efficient in terms of disk usage (if you have partitioned/formatted your disk to efficiently store large files). In short, there is no free lunch, and you have to decide what is more important to you: saving time or saving disk space... I've just investigated this because I am doing a transition of our network filesystem away from NFS and had to resolve some performance issues as well. Volkmar On Wed, 4 Apr 2007, Paul Macey wrote: > Hi Jérôme > > I just wrote something to split 4D to 3D; run the attached script > (cspm_im_4Dto3D, from SPM5 only) and it will prompt for a 4D file to split. > You can also use it in batch mode with a couple more options (see help). The > 3D files should be the same as in the 4D file, so I don't think you will > loose anything by converting. > > Best wishes, > Paul > > Jérôme Redouté wrote: >> Dear SPMers, >> My parameters estimation process is extremely slow. Could this slowness >> be due to using a 4D-Niftii dataset? >> In order to check that, I would like to convert my sw_xxxx.nii 4D files >> into a set of 3D files. >> My questions are: >> -SPM has a function to convert 3D -> 4D , but is the reverse function >> available? Where can I find such a converter? >> -These images are preprocessed (realignment, normalisation, smoothing), do >> I risk to lose these parameters by converting to 4D to 3D? >> Thanks for your help >> Jerome >> > -- Volkmar Glauche - Department of Neurology [log in to unmask] Universitaetsklinikum Freiburg Phone 49(0)761-270-5331 Breisacher Str. 64 Fax 49(0)761-270-5416 79106 Freiburg http://fbi.uniklinik-freiburg.de/