Hi Xue and SnPMers,
At 05:13 PM 6/28/2005 -0700, HUA,XUE wrote:
>My study is looking at the regional tissue growth during normal brain
>development. I calculated the annualized tissue change map based on the
>Jacobian map of the deformation field. Then I examined the mean at each
>voxel using t-test and see if it is away from zero.
>
>I want to use SnPM to correct for multiple comparisons across the whole
>brain volume. I followed the "fMRI Example" on the SnPM website which I
>thought is a very much the same application. However, I keep getting
>error messages. First I thought it was a memory issue. But when I cut
>down to two subjects, I still get error message and could not complete
>the analysis. I have 13 subjects and each scan has the dimension of 199 x
>199 x 199. The size for each voxel is 1mm cube. I obtained the annualized
>tissue change maps using Matlab6 and the results were saved in the .img
>(unsighed int)file. The header files were generated by makeaheader
>command. I am running the analysis on a Windows pc (Pentium 4 CPU 3.2
>GHz, 1GB of RAM). The following is an outline of the error messages. I
>could not diagnose the problem and hope I could find out an answer here.
>I greatly appreciate for your time!
It sounds like you are simply running out of memory. To conserve memory
usage, SnPM has the slice-by-slice mode as opposed to the volumetric mode.
Unfortunately SnPM doesn't give you a choice to work with the
slice-by-slice mode unless you have more than 16 images. To correct this
problem, you can change the variable called "nMax4DefVol" in snpm_ui.m to a
smaller number, say 5, instead of 16 (default). By doing so, SnPM will ask
you if you would like to work using the "slice-by-slice" mode or
"volumetric" mode.
If this doesn't solve the memory problem, then probably you don't have
enough memory. Another solution is to re-slice your images to 2x2x2 mm
voxel size instead of 1x1x1mm. But reducing the image resolution (in term
of voxel size) isn't very appealing though.
Good luck!
-Satoru
Satoru Hayasaka ==============================================
Post-Doctoral Fellow, MR Unit, UCSF / VA Medical Center
Email: shayasak_at_itsa_dot_ucsf_dot_edu Phone:(415) 221-4810 x4237
Homepage: http://www.umich.edu/~hayasaka
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