12.5. DICOM Data and Coordinates

12.5. DICOM Data and Coordinates
	Chapter 12. Excursion: Image Processing in ML

A mixed type are DICOM "coordinates". They are mostly world coordinates but refer to the patient axes.

Based on the patient's main body axes (axial/transverse, coronal, sagittal)
Measured as 1 coordinate unit = 1 millimeter
Right-handed
Not standardized regarding their origin

Figure 12.4. World Coordinates in Context of the Human Body

The DICOM (Digital Imaging and Communications in Medicine) standard is a data format that groups information into data sets. This way, the image data is always kept together with all meta information like patient ID, study time, series time, acquisition data etc. The image slice itself is essentially just another tag with pixel information.

DICOM tags have unique numbers, encoded as 2x4 numbers in hexadecimal notation (0000,0000). The first four numbers are the data group, the second four numbers the data set/tag.

	Note
	Although DICOM is a standard, often the data that is received / recorded does not follow the standard. Wrongly used tags or missing mandatory tags may cause problems in data processing.

Some typical modules for DICOM handling:

DirectDicomImport is a module for DICOM import that reads images directly from slices, without an intermediate representation.
It has a lot of options to control the import process, which can, e.g., determine which slices are combined into an image stack.
DicomImport is a new module for DICOM import. The new implementation does not yet provide all known functionalities from DirectDicomImport, most of them will be added in future releases. Its main advantage is that the import process is faster and happens asynchronously.
You can view the image-wide DICOM tags with the module DicomTagBrowser.
You can view and cut out frame-specific tags with the module DicomFrameSelect.
You can modify DICOM tags with the module DicomTagModify.
You can also create a new DICOM header for an image file with the ImageSave module, tab Options, Save DICOM header file only.
Saving of loaded DICOM data to the filesystem or sending to a PACS (Picture Archiving and Communication System) is possible with the DicomTool macro module.
Basic support for querying and receiving DICOM data from a PACS is available through the DicomQuery and DicomReceiver modules.

	Tip
	For handling and manipulating DICOM data, the DICOM toolkit “DCMTK” (DICOM@offis) is recommended. Parts of this toolkit are also used in MeVisLab.

Figure 12.5. The DICOM Tag Browser


12.4. Affine Transformations		12.6. Coordinate Systems in the MeVisLab GUI