Dear SPM-ers,
For our single subject PET data we are interested in the resolution of our
'raw' images (e.g. camera resolution). We tried to obtain this raw FWHM by
doing a statistical analyses on the images which are realigned but not
normalised or smoothed (avoiding the introduction of extra smoothing by one
of them) and read the FWHM from the spm output.
As always, during the realignment, we created a 'mean image only'(I)
resulting (during the statistics) in the following error:
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SPM99: spm_spm_ui (v2.26) 15:40:05 - 09/07/2001
=======================================================================
Mapping files : ...done
??? Error while evaluating uicontrol Callback.
>> ??? Error using ==> spm_spm_ui
images do not all have same orientation & voxel size
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We speculated that the statistics needs the information from the image files
and does not bother about the *.mat files (containing the orientation and
voxel size information). So we created during the realignment the 'mean
image + all images'(II) and used the r*.img files for the statistical
analyses. No error messages occurred and we found an FWHM of 5.0 5.7 5.6 .
However, for the normal statistical inference we identically normalised and
smoothed (10mm) the two different sets of realigned images (I and II).
Now we find in situation (I) a FWHM of: 9.5 10.4 10.8
and in situation (II) a FWHM of: 9.6 10.6 11.0
Of course this is a very small difference. But the question is: is the FWHM
of 5.0 5.7 5.6 our raw camera resolution. Or is here already some smoothness
introduced by the realignment (which is suggested by the results after the
normal statistical analyses)? If yes, does anyone know how much?
If the realignment introduces some smoothness, can the raw resolution then
be calculated by the formula given by Karl Friston:
FWHM^2 = FWHM{applied)^2 + FWHM{intrinsic)^2
(http://www.jiscmail.ac.uk/cgi-bin/wa.exe?A2=ind9909&L=spm&P=R10782)
if we knew how much smoothness was introduced in the realignment?
Or is there another way to obtain the raw resolution of the images?
Thanks in advance for your time and help,
Simone.
--
A.A.T.S. Reinders
University Hospital of Groningen
The Netherlands
