Thank you so much, Mark!
I just checked my data. It is same to your assumption that most of my value is positive and grey matter part is usually around 1000 (most are lower than 1000, about several hundreds).
Now, I feel much better to my data.
Thanks, again!
Xiaochu
-----Original Message-----
From: Mark Jenkinson [mailto:[log in to unmask]]
Sent: 2008年1月2日 12:23
To: [log in to unmask]
Subject: Re: [FSL] The unit of VBM result
Hi,
Gwen or others can correct me if I'm wrong, but I think that all
segmentation results
in fslvbm are scaled by a factor of 1000 in the native space and then
for the _mod_
images they are again scaled by the local Jacobian.
If this is the case then values up to 5233 are possible and not
unreasonable,
although I'd expect most of your voxels to have values more like 1000
in grey matter.
Negative values are worse and probably indicate negative Jacobian
values which
can occur but should be very rare and hopefully in uninteresting
places. Check
that you do not have many voxels with values less than zero.
If most of your values are positive and of the order of 1000 in grey
matter, then
I think everything is probably fine.
All the best,
Mark
On 1 Jan 2008, at 20:17, Zhang, Xiaochu (NIH/NIDA) [F] wrote:
> Thank you very much for your response!
>
> However, I just use fslstats to check my original data (i.e.,
> “GM_mod_merg_s3.5.nii.gz”). It is form -462 to 5233!
> Is there something wrong?
>
> Could you please give me some suggestions which one I need check more?
>
> Thank you very much!
>
> Xiaochu
>
> From: Lynne Gauthier [mailto:[log in to unmask]]
> Sent: 2007年12月31日 14:05
> To: [log in to unmask]
> Subject: Re: [FSL] The unit of VBM result
>
>
>
> The value of each voxel from the segmentation should be between 0
> and 1. Closer to 1 means more grey matter. Perhaps you have the
> sum for all the voxels in the ROI, not the average?
>
>
>
> On Dec 30, 2007, at 4:37 PM, Zhang, Xiaochu (NIH/NIDA) [F] wrote:
>
>
>
> Hi FSL experts,
>
> I am working on the VBM analysis on my data. Now I want to do some
> individual analysis. So I got the mean value of one ROI in each
> subject. The value is usually about several hundred. I think the
> higher value means the higher density of grey matter. Is it correct?
>
> Additionally, I was confused on the unit of these values. I read
> some VBM papers and found their data is usually 0-1.
>
> who can help me?
>
> Thank you very much
>
> Xiaochu
>
>
>
> Lynne Gauthier
>
> Graduate Research Associate
>
> Neuroimaging Lab
>
> CI Therapy Research Group
>
> University of Alabama - Birmingham
>
> 857-998-7785
>
> [log in to unmask]
>
>
>
>
>
>
>
>
>
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