Orientation information in DICOM files from Bruker and Siemens are always subject to correct orientation specification by the MR technician. Assuming correct orientation specification during setup the DICOM orientations are correct.
Quadruped vs biped
It should be noted the quadrupeds and bipeds have different, incompatible anatomical orientations. This means that anatomical labels generated by a viewer designed assuming a biped subject will be inappropriate when viewing quadruped images. This is not an error in the DICOM orientation information, it is an error in the viewer software. In such cases it is not advisable to manipulate orientations to ensure label correctness as it will cause issues when using the data in application that correctly interpret quadruped and biped data.
Sphinx
Sphinx orientation is not an DICOM allowed orientation for biped subjects as it results in an anatomical head orientation that is different the anatomical body orientation, i.e. the orientation is anatomy specific, which is not supported by any MR vendors. This is further complicated by the fact that there is generally no body orientation allowed that would result in the correct head orientation being recorded, due to the fact that bipeds are typically geometrically precluded from anterior-posterior body orientation along the magnet bore. This mean bipeds imaged in sphinx position will never have the correct orientation in the DICOM files. However, if the correct body position of the subject was specified correctly then the following correction is always applicable to obtain the correct head orientation.
- X_actual = X_dicom
- Y_actual = -Z_dicom
- Z_actual = Y_dicom
This is equivalent to the following rotation matrix
| 1 | 0 | 0 |
| 0 | 0 | -1 |
| 0 | 1 | 0 |
This rotation needs to be applied to all DICOM orientation dependent fields, including
- Image Plane Module
- Plane Orientation (Volume) Module
- (0010,2210) Anatomical Orientation Type
- (0018,5100) Patient Position
- (0020,0037) Image Orientation Patient
- (0020,0032) Image Position Patient
- (0028,9520) Image to Equipment Mapping Matrix
- (0018,9117) MR Diffusion Sequence
- (0018,9090) Velocity encoding direction
- (0018,9105) Slab Orientation
- (0018,9106) Slab Position
- (0018,9255) ASL Slab Orientation
- (0018,9256) ASL Mid Slab Position