This works.
--- On Wed, 7/8/09, John Ashburner <[log in to unmask]> wrote:
> From: John Ashburner <[log in to unmask]>
> Subject: Re: [SPM] negative modulated data from DARTEL
> To: [log in to unmask]
> Date: Wednesday, July 8, 2009, 2:29 PM
> Is this from the Normalise to MNI
> space option. If so, then the fix is
> to change line 240 of
> spm8/toolbox/DARTEL/spm_dartel_norm_fun.m from:
>
>
> scal =
> det(NI.mat(1:3,1:3))/det(NO.mat(1:3,1:3)); %
> Account for vox sizes
>
> to:
>
> scal =
> abs(det(NI.mat(1:3,1:3))/det(NO.mat(1:3,1:3))); % Account
> for vox sizes
>
> The reason for this (I hope) is that the original images
> have a
> voxel-to-world transform with a positive determinant (so a
> positive x
> voxel size when displayed), whereas the spatially
> normalised images have
> a negative determinant for the voxel-to-world transform
> (the same as the
> template data). Your suggestion therefore makes
> sense.
>
> The negative value thing will be fixed in the next set of
> updates.
>
> Best regards,
> -John
>
> On Tue, 2009-07-07 at 19:18 +0000, cliff macnab wrote:
> > Hi experts,
> >
> > I got negative modulated data from DARTEL. Their
> values at background are close to zero, but negative at
> brain area. Does the negative value come from negative voxel
> size or something wrong? (I found the nii images have
> negative x-direction voxel size).
> >
> > Thanks for any explanation,
> >
> >
> > Cliff
> >
> >
> >
> >
> --
> John Ashburner <[log in to unmask]>
>
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