[Insight-users] Setting the spacing of images for rigid registration

[Karthik Krishnan]

Regsitration is done in physical space, So it does take into account the
spacing. (This allows a high resolution image of a patient to be registered
to a low res image).

As a starting point, you might want to simply omit the registration step.
Resample the moving image to the fixed, with an "InitialTransform" and see
how they overlay with each other. Figure out a good "InitialTransform" . And
then start off with trying to register them, with this initial transform. My
guess is that in manually changing the spacing, you're initial transform
(which is in physical space) places you elsewhere.

--
karthik

On 2/16/07, Sims Richard (RKB) Clinical Scientist <Richard.Sims at uhcw.nhs.uk>
wrote:
>
>  Hi all
>
>
>
> I have ammended one of the example codes provided with ITK to perform
> rigid registration using a Centered Rigid 2D Transform with a Mattes Mutual
> Information Metric. My fixed and moving images are both bitmaps which of
> 512x512 size but have different pixel spacing, 0.898mm/pixel for the fixed
> image and 0.527mm/pixel for the moving image. I have successfully
> registered these images using a Similarity 2D Rigid Transform (the moving
> image being re-scaled to the fixed image), but would like to rigidly
> register them without scaling by accouting for their different pixel
> spacing. I've tried to explicitly define the spacing of the pixels using the
> following code:
>
>
>
> FixedImageType::SpacingType spf;
>
> MovingImageType::SpacingType spm;
>
> FixedImageType::PointType orf;
>
> MovingImageType::PointType orm;
>
>
>
> spm[0]=0.527344;
>
> spm[1]=0.527344;
>
> //spf[2]=1.000000;
>
>
>
> orf[0]=0.0;
>
> orf[1]=0.0;
>
> //orf[2]=0.0;
>
>
>
> spf[0]=0.898438;
>
> spf[1]=0.898438;
>
> //spm[2]=1.000000;
>
>
>
> orm[0]=0.0;
>
> orm[1]=0.0;
>
> //orm[2]=0.0;
>
>
>
> fixedImage->SetSpacing(spf);
>
> fixedImage->SetOrigin(orf);
>
> movingImage->SetSpacing(spm);
>
> movingImage->SetOrigin(orm);
>
>
>
> But it doesn't seem to have an effect... I'm guessing it has something to
> do with the resample image filter, but have reached a stumbling block...
> could anyone give me a pointer in the right direction?
>
>
>
> Many thanks,
>
> Richard.
>
>
>
>
>
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