I think the streak artifacts you refer to are actually aliasing
effects from the way the "modulated" images are generated when you
normalise to MNI space. The reason they are more apparent is that
your spatially normalised images are of a similarly high resolution to
the original images. These effects should disappear when you smooth.
Here is a response to an earlier related question...
> (1) When warping to MNI space with a low-resolution image, you get a
> striped pattern that is co-planar with the acquisition plan. Between
> the stripes the values of the voxels are 0. This was confirmed by
> zooming in and using NN interpolation in the checkreg function. This
> pattern does not exist when warped to the DARTEL template. Why does
> warping to MNI space lead to 0 value voxels within the brain? This
> seems to be very problematic for processing data.
This option is usually used for anatomical scans, which have a higher
resolution. My aim was to exactly preserve the volumes of tissue, so
instead of sampling the image using the inverse transform, and then
scaling according to the Jacobian determinant, the approach here pushes
the voxels to their new locations. It can lead to slight aliasing
effects for anatomical scans, but these are usually dealt with by the
smoothing. For low resolution images, the aliasing effects are more
extreme, which is what you are seeing.
best regards,
-John
On 5 March 2012 16:38, Shail Segobin <[log in to unmask]> wrote:
> Dear All,
>
> I was wondering how the rc* images are generated? Is it a resampling from
> rc* images that are 1.5mm3 isotropic to start with?
>
> My problem is the following:
>
> I have streak artefacts on my modulated images when I segment them using
> the template upsampled from 1.5mm to 1.0mm. I wanted to know whether using
> the upsampled template is creating those artefacts or whether I am missing
> something....
>
> Thank you for your help
> Shail
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