[Insight-users] 3D Image Volume Origin

[Frank Miller]

Hi Andrew,

The code in 2.4.0 does not set the origin of the image correctly 
according to the DICOM standard. See Section C.7.6.2.1 in PS 3.3.

    http://medical.nema.org/dicom/2004/04_03PU3.PDF

The comments in the 2.4.0 code lead me to believe that this was done 
intentionally but I do not understand the reasoning. My suspicion is 
that this code was correct at one time but then the DICOM standard 
changed. If this is true, then it might be the case that your images 
conform to the old standard.

Frank

Andrew Li wrote:
> Hi, ITK users:
> 
> We are moving up ITK package from 2.4.0 to 2.6.0.
> There are some problems after ITK library is switched.
> 
> Those problems seem related to the center of the 3D volume, which is
> related to Origin and Direction of the 3D volume.
> 
> We just start to investigate the problems and we noticed that there are
> some changes made in IO/itkGDCMImageIO.cxx
> 
>   In ITK 2.4.0 version: Date:      $Date: 2005/11/29 21:58:28 $
>   // DICOM specifies its origin in LPS coordinate, regardless of how
>   // the data is acquired. itk's origin must be in the same
>   // coordinate system as the data. This code transforms the DICOM
>   // origin into the itk origin. The itk origin is computed by
>   // multiplying the inverse(transpose) of the direction cosine times
>   // the dicom origin.
>   vnl_vector<double> itkOrigin(3), dicomOrigin(3);
>   vnl_matrix<double> dicomDirection(3,3);
>   dicomOrigin[0] = header.GetXOrigin();
>   dicomOrigin[1] = header.GetYOrigin();
>   dicomOrigin[2] = header.GetZOrigin();
>   for (unsigned int ii = 0; ii < 3; ii++)
>     {
>     dicomDirection[0][ii] = rowDirection[ii];
>     dicomDirection[1][ii] = columnDirection[ii];
>     dicomDirection[2][ii] = sliceDirection[ii];
>     }
>   itkOrigin = dicomDirection * dicomOrigin;
>   m_Origin[0] = itkOrigin[0];
>   m_Origin[1] = itkOrigin[1];
>   m_Origin[2] = itkOrigin[2];
> 
>   While in ITK 2.6.0 version: Date:      $Date: 2006/03/08 18:28:57 $
>   // Dicom's origin is always in LPS
>   m_Origin[0] = header.GetXOrigin();
>   m_Origin[1] = header.GetYOrigin();
>   m_Origin[2] = header.GetZOrigin();
> 
> Could anyone tell us the reason of the changes and impact of the
> changes?
> Thank you all for your help!
> 
> -Andrew
>  
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