1. NA-MIC National Alliance for Medical Image Computing http://na-mic.org Adding Orientation to itkImage

2. National Alliance for Medical Image Computing http://na-mic.org Motivation

3. National Alliance for Medical Image Computing http://na-mic.org Image Coordinate Systems Coordinate systems are an important part of any medical application. Medical scanners create regular, "rectangular" arrays of points and cells. The topology of the arrays is implicit in the representation. The geometric location of each point is also implicit.

4. National Alliance for Medical Image Computing http://na-mic.org vtk and itk images vtk and itk store meta-information that can be used to convert between image coordinates (i-j-k) and world coordinates (x-y-z). Each image has an origin that is a 3-D (n-D for itk) vector. The origin (x-y-z) specifies the world coordinate of the first point in memory. The spacing specifies the distance between points along each axis. Using the spacing and origin, the transformation between i-j-k and x-y-z is a fast, simple computation. –x(yz) = origin + i(jk) * spacing; –i(jk) = (x(yz) - origin) / spacing;

5. National Alliance for Medical Image Computing http://na-mic.org Requirement: Location + Orientation space: right-anterior-superior space origin: (117.5,-93,119) space directions: (-0.859375,0,0) (0,0,-0.859375) (0,5,0) none right anterior superior (RAS) fast medium slow (image)

6. National Alliance for Medical Image Computing http://na-mic.org Proposed extensions to itk::Image Add an itk::Matrix containing direction cosines The i-j-k -> x-y-z transformation could include the orientation in the computation. Adding the matrix will not change the existing API. Almost all index to point calculations are confined to itk::Image. The transformations in matrix form are: –XYZ = T o * R c * S s * IJK where T o is a translate to the origin, R c is the matrix of direction cosines and S s is a scale matrix of spacings. There are performance considerations, so the implementation may cache some internal matrices and state.

7. National Alliance for Medical Image Computing http://na-mic.org Next Steps Continue discussion on the Wiki –NAMIC Wiki:Community Coordinate Systems