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

[Christoph Palm]

Hi Richard,

it would be easiest and most correct to use an image format, that stores
your spacing implicitely, e.g. the meta image format of ITK. Reading
such images, your spacing is correctly set from the beginning.
And note, the registration is computed in real world coordinates and
is always dependend on the spacing. What image format do you use?
Otherwise use the ChangeImageInformationFilter to change the spacing
of your images.

Regards

Christoph

On Fri, 2007-02-16 at 17:13 +0000, Sims Richard (RKB) Clinical Scientist
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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