Discrepancy between vtkImageReslice and Clipping Planes for gantry tilt corrected data

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1

I have 3D volumetric data (ie. CT datasets), where I want to show a reconstruction plane using vtkImageReslice and cut the volume at that same position using the SetClippingPlanes function of the vtkVolumeMapper. This works well in general, but I run into problems with gantry tilted data (For the correction I use ITK and a shear matrix). The slice displayed by vtkImageReslice seems accurate, but the volume is cut at the wrong position:

grafik
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I use exactly the same coordinates for both the reslice and the cutting plane.

Any ideas what the problem might be? Why are coordinates seemingly interpreted differently in these two cases? Thank you very much.

2

If the gantry-tilt correction is done before the data is loaded into VTK, then it seems that the gantry tilt should be unrelated to the problem that you are seeing. Is the same vtkImageData used for both the input into vtkImageReslice, and the input into the vtkVolumeMapper?

Do you use any matrices in VTK itself, for example do you use SetUserMatrix() or SetUserTransform() with the vtkVolume? If so, what are the values in these matrices (specifically, are they orthogonal matrices?)

I might need to see the code to get an idea of where the problem is.

3

Hi David,
I agree with you that the gantry tilt should be unrelated. Furthermore, I also use ITK to reorient sagittal / coronal images to axial, and there are no such problems in these cases.
I also do not use any user transforms.
I’d probably have to isolate the problem in a sample project, and will share it if I encounter it there.