The Inventory Information Object Definition (Section A.88 “Inventory IOD” in PS3.3) specifies a structure capable of encoding an Inventory of all Studies, Series, and Instances in a repository. The IOD is structured hierarchically using Sequence Attributes. Within the Inventory is a sequence of Study records, within each of which is a sequence of Series records, and within each of those is a sequence of Instance records. Each "record" is a set of key Attributes describing the Studies, Series, and Instance entities in a repository, and the mechanisms for accessing the stored SOP Instances.
The IOD entity-relationship model is shown in Figure YYYY.3-1. The Inventory is created by an identified piece of Equipment. The content of the Inventory follows the Study Root Query/Retrieve Information Model (see Section C.6.2.1 in PS3.4), with Patient and Imaging Service Request information treated as Attributes of the Study. The Imaging Service Request Information Entity is not explicitly modeled in other Composite IOD E-R models, but it is specifically identified here as its Attributes, such as Accession Number, are typically important in repository management.
Note
There is a potentially complex relationship between the Study and Imaging Service Requests in the real world (e.g., see [IHE RAD TF-2] Section 4.6.4.1.2.3 Relationship between Scheduled and Performed Procedure Steps). However, the Inventory Information Model follows the basic Study Information Model and supports only a single Accession Number representing an Imaging Service Request (see Section C.7.2.1 “General Study Module” in PS3.3). Note that if a Study has multiple associated Imaging Service Requests, the request Attributes may be encoded at the Series level in the Request Attributes Sequence (0040,0275). The Inventory IOD includes the Request Attributes Sequence to support this use.
Figure YYYY.3-1 is reproduced from Figure 7.13.6-1 “Inventory Information Model E-R Diagram” in PS3.3
These IOD Information Entities include all the required Attributes specified for Query processing by the repository system (see Section C.6 “SOP Class Definitions” in PS3.4). An Inventory is thus a standard DICOM representation of the key content of a repository system database for DICOM SOP Instances in the repository. Other aspects of such databases, such as data for workflow queues, are out of scope of the Inventory IOD.
The IOD allows Inventories at three Inventory Levels - with only Study records, with Study and Series records, or with Study, Series, and Instance records. While many uses will require Inventories with Instance level records, production of a Study or Series level Inventory may be significantly faster and may be sufficient for some uses.