Dear Alain,
the choice of registration shouldn't affect the (average) intensity, though for a given voxel in the new (standard?) space it could of course be quite different.
Which of these is it you are seeing, changes in average or changes in specific individual voxels?
Jesper
On 23 Oct 2013, at 15:02, Alain Imaging <[log in to unmask]>
wrote:
> Dear all,
>
> I recently worked with PET images of an amyloid tracer.
>
> I was trying to compare two different ways for uptake quantification, one using a PET template, the other using images in native space.
>
> For different reasons (among others some reviewer's comment) I tried both linear and non linear registration of the PET images to the template.
> I was quite surprised to see that the intensity value are greatly different using the two methods.
> In particular the images registered in a non linear fashion present higher values than the images linearly registered (let's say that the difference in values is of 500 in a scale that range from 0 to 3000). Why this happens? I mean, leaving the interpolation method unchanged, why the type of _spatial_ transformation should affect the values ?
>
> And a semi-related question: could the number of degree of freedom in a linear registration affect the values of the final image, once again leaving unchanged the interpolation method ?
>
> Thank you in advance for any answer or tip
>
> Alain
|