[Insight-users] gantry tilt compensation

[Luis Ibanez]

Hi Zsolt,

The gantry tilt will be equivalent to a Shearing
in the Affine Transform.  A typical shearing effect
in a 2D transform will generate a matrix of the form


     1  A
     0  1

or

     1   0
     B   1


Where "A", and "B" will be shearing factors and can
be positive or negative.

The AffineTransform in ITK
http://www.itk.org/Insight/Doxygen/html/classitk_1_1AffineTransform.html
doesn't have an explicit method for setting shearing factors.
You can however setup your matrix and then pass it to the
transform with the SetMatrix() method.

Once you configure your Affine transform, you may want to
use the ResampleImageFilter
http://www.itk.org/Insight/Doxygen/html/classitk_1_1ResampleImageFilter.html
in order to resample your image into a rectilinear grid.

You are strongly encouraged to read the chapter on image
resampling from the ITK SoftwareGuide

     http://www.itk.org/ItkSoftwareGuide.pdf



   Regards,


     Luis



-------------------
Erő Zsolt wrote:
> I am trying to write a small program that transforms a volume of
> slices made with tilted CT head into a standard (rectangular) volume
> array, because no algorithms support such type of volumes in ITK or
> VTK (as long as I know). I know, there is an affine transform in ITK,
> but don't know what to do with it. Could you help me how to use it
> (not for coding but mathematically)? I know the tilt angle from the
> DICOM file, but don't know how can I reverse-transform on the
> transformed volume. Any web resource could be useful, I looked up
> google, but found nothing usable.
> 
> Thanks,
> Zsolt Ero
> 
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