[Insight-users] DICOM vs ITK orientation

[Tim Allman]

Actually, as far as I can tell, ITK does not use DICOM orientation.

Encoded in the DICOM tag "Image Orientation (Patient)" are two 3D 
vectors. The first gives the orientation in 3D space if the first row of 
the image and the second gives the orientation of the first column. (If 
the image is 3D, the third axis, which is normal to the plane of the 
other two, is calculated as the cross product of the first two vectors). 
Because a 2D image is embedded in 3D space, it needs the 3D vectors for 
correct orientation.

The orientation (direction in ITK) in ITK is given as a 3x3x3 matrix in 
a 3D image which is correct. However, a 2D image contains only a 2x2 
direction matrix instead of the 2x3 matrix implied by the DICOM tag. The 
orientation is lost when extracting a slice from a 3D image using the 
itk::ExtractImageFilter regardless of the direction collapse strategy.

Please let me know if my analysis is incorrect.

Thanks,
Tim



On 13-06-19 06:37 PM, Bill Lorensen wrote:
> ITK uses the DICOM orientation information.
>
>
> On Wed, Jun 19, 2013 at 2:13 PM, Tim Allman <dr.tim.allman at gmail.com 
> <mailto:dr.tim.allman at gmail.com>> wrote:
>
>     I have been trying to make sense of both systems of describing
>     orientation but without success. Is there a function or some
>     documentation somewhere that describes how to convert one to the
>     other?
>
>     Thanks,
>     Tim
>
>     -- 
>     Tim Allman, Ph.D.
>     35 Margaret Street,
>     Guelph Ontario N1E 5R6
>     Canada
>
>
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-- 
Tim Allman, Ph.D.
35 Margaret Street,
Guelph Ontario N1E 5R6
Canada

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