The Patient Orientation (0020,0020) relative to the image plane shall be specified by two values that designate the anatomical direction of the positive row axis (left to right) and the positive column axis (top to bottom). The first entry is the direction of the rows, given by the direction of the last pixel in the first row from the first pixel in that row. The second entry is the direction of the columns, given by the direction of the last pixel in the first column from the first pixel in that column. Shall be consistent with Image Orientation (Patient) (0020,0037), if both Attributes are present and Patient Orientation (0020,0020) is not zero length.
If Anatomical Orientation Type (0010,2210) is absent or has a value of BIPED, anatomical direction shall be designated by abbreviations using the capital letters:
If Anatomical Orientation Type (0010,2210) has a value of QUADRUPED, anatomical direction shall be designated by the abbreviations using capital letters:
LE (Le or Left)
RT (Rt or Right)
CR (Cr or Cranial)
CD (Cd or Caudal)
PR (Pr or Proximal)
DI (Di or Distal)
PA (Pa or Palmar)
PL (Pl or Plantar)
Notes: 1. These abbreviations are capitalized versions of those defined in Smallwood et al for describing radiographic projections. Because of the Code String (CS) Value Representation of the Patient Orientation (0020,0020), lowercase letters cannot be used.
2, It is unfortunate that the conventional veterinary abbreviations (e.g., R for rostral and Rt for right) differ from those chosen for humans for DICOM usage (e.g., R for right), but confusion with in the respective human and animal domains will be reduced. Hanging protocols may need to account for the difference by checking for the correct species.
3. Smallwood et al define an O (Oblique) abbreviation, which is useful for describing radiographic projections, but do not specify its use for directional terms, and hence it is not included here for describing the row and column directions.
4. The terms “anterior” and “posterior” are commonly used in vertebrate zoology to describe the cranial and caudal directions respectively, the veterinary terms are used in preference here, also in order to avoid confusion with the contradictory human use of anterior and posterior to mean ventral and dorsal.
5. For animals other than quadrupeds, for example, birds and fish, it is anticipated that the same nomenclature can be logically extended to describe, for example, wings and fins.
Each value of the orientation attribute shall contain at least one of these abbreviations. If refinements in the orientation descriptions are to be specified, then they shall be designated by one or two additional abbreviations in each value. Within each value, the abbreviations shall be ordered with the principal orientation designated in the first abbreviations.
Notes: 1. For bipeds, since each abbreviation is a single character, no delimiter is required within a single value and none is used. For quadrupeds, though lowercase letters cannot be used, delimiters are not necessary within a single value to eliminate ambiguity, since the abbreviations used are sufficiently distinct, and can be parsed from left to right with a single character of lookahead.
2. E.g., a medio-lateral oblique projection of the left breast of a human might be encoded with Patient Orientation values of “A\FR” rather than “A\F”, since the plane is obliquely inclined such that the colums are directed both downwards and medially, which for a left breast is towards the right, though the downwards direction is the principal column orientation.
3. E.g., a right dorsal-left ventral oblique view of a quadruped’s abdomen might be encoded with Patient Orientation values of “LTV\CD”, rather than “LT\CD”, since the plane is obliquely inclined such that the rows are directed both to the left and ventrally, though the left direction is the principal row orientation. The abbreviations “LTV”, “LT” and “CD”, correspond to the designations in Smallwood et al of “LtV”, “Lt” and “Cd”, respectively