Dear Jie
Assuming you have smoothed the data, then most likely there is some type of
noise in your dataset. You could try plotting some of the time series or
looking at it with tools such as tsdiffana. See this page:
http://imaging.mrc-cbu.cam.ac.uk/imaging/DataDiagnostics
Darren
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping)
> [mailto:[log in to unmask]] On Behalf Of J Zhuang
> Sent: Tuesday, April 29, 2008 9:11 AM
> To: [log in to unmask]
> Subject: [SPM] "dot" problem of brain activation in SPM5
>
> Dear SPM experts,
>
> I met an analysis problem in the random effect of one of my
> experimental conditions with SPM5. The activation is made up
> of many separated tiny dots, rather than one or several big
> blobs (see the attachment). This is the only problematic case
> among all my experimental contrasts within the same model.
> Here is some further information,
>
> The problematic contrast:
> FWHM = 1.6 1.6 1.5 mm mm mm; 0.8 0.8 0.8 {voxels};
> Volume: 1379328; 172416 voxels; 337791.5 resels Voxel size:
> 2.0 2.0 2.0 mm mm mm; (resel = 0.47 voxels)
>
> One of the normal contrasts:
> FWHM = 12.5 12.9 12.2 mm mm mm; 6.3 6.4 6.1 {voxels};
> Volume: 1379328; 172416 voxels; 649.0 resels Voxel size: 2.0
> 2.0 2.0 mm mm mm; (resel = 246.41 voxels)
>
>
> I checked the fixed effect of this specific contrast for each
> subject, but did not find any similar "dot" problem. I feel
> puzzled with it. Could anybody be kind to give me a hint on
> the reason and possible solution? Any help is greatly appreciated!
>
> Cheers,
> Jie
>
>
>
|