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 orientation ² ³, 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.[3] Orientation means "close to", axes are not always aligned with coordinate system axes.


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.

In physical space 3D view slices are always drawn as defined in DICOM file.

For DICOM classic series slices are sorted by Image Position (Patient) and Image Orientation (Patient).

Fig. 1

Differences in orientation terminology