Dear John,
do you only have data from a single patient? If so, then with a paired
t-test, the degrees of freedom is 0, hence the awkward display in SPM...
Try again when you have at hand pre and post data from more patients.
Best regards,
Guillaume.
On 11/12/15 15:36, John Metzcar wrote:
> Hi All,
>
> I am interested in using SPM to compare before and after radiotherapy
> MRI data sets. I have processed before and after ADC maps with
> realignment and reslicing and before and after T1 images through the SPM
> VBM preprocessing tools. In both cases, I have used a paired t test to
> analyze the before and after images. When using this model with either
> comparison, unfortunately, I get only "blob" and very few if any voxels
> that are unaffected. This seems like too much of a good thing, as I
> can't draw many conclusions from every voxel lighting up. Any ideas on
> how I could get some more productive information out of the scans? I
> also have T2 anatomical, DWI, and perfusion images if those might be
> better suited for looking for the change from the therapy. Just so it
> is noted, the data was obtained from a pediatric patient, so there
> should be some change; I just wasn't expecting complete change after all
> the preprocessing in particular on the VBM. Perhaps I am missing some
> important step, parameter, or knowledge and I bet that you folks can
> help out.
>
> Attached is a screen capture of SPM with the results and the model
> specified as it was a used to generate them. This happened to be the
> gray matter segment comparison of the VBM preprocessing. In this
> example in particular, the FWE p value was set to 1E-8 and voxel extent
> set to 15.
>
> Thank you,
>
> John Metzcar
> Medical Physics, 2017
> Indiana University, Bloomington
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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