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
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,
> 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
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