Orientation

Orientation codes

The orientation code maps the pixel coordinate system I (column) J (row) K (slice) to right-handed coordinate system X Y Z. Characters R (right), L (left), A (anterior), P (posterior), I (inferior), S (superior) identify from direction.

RAI ¹, the default orientation², means

  • X: patient Right to left
  • Y: patient Anterior to posterior
  • Z: patient Inferior to superior
[1] Same orientation is called ITK RAI , DICOM LPS or Nrrd left-posterior-superior. Sometimes towards notation is used, right to Left, etc.[2] 48 orientations are defined, but there are 24 valid orientation for DICOM. DICOM defines in Image Orientation (Patient) vectors for X and Y (6 direction cosines), Z is right-handed cross product. It is not relevant for DICOM classic series, they are usually sorted by Image Position (Patient) and Image Orientation (Patient). For multi-frame files Aliza will take care of correct export.

DICOM

Spatial position, orientation and geometry of DICOM series (CT, MR, PET and other IODs) are examined. If the image is recognized as uniform volume, it receives green orientation code in information widget.

Fig. 1

Differences in orientation terminology