IOD (Information Object Definition)

The DICOM template of tags required for a given object type, such as a CT Image.

An IOD (Information Object Definition) is the DICOM “schema” for one kind of object, such as a CT Image or an RT Structure Set. The IODs are defined in PS3.3 of the standard.

An IOD is built from modules (Patient, General Study, Image Pixel and so on). Each module is Mandatory, Conditional or User optional for that IOD, and each attribute inside a module has a type that says whether it must be present and whether it may be empty. The SOP Class pairs an IOD with a service, which is how a receiving system knows what a file should contain.

Conformance and IOD validation check a file against the IOD for its SOP Class, so a downstream system won’t reject it for a missing required tag.