DICOM PS3.17 2022c - Explanatory Information

YYYY.7.4 Incremental Inventories

Like all DICOM composite objects, Inventory SOP Instances are static, so an Inventory of a repository in dynamic operation can never be complete. The challenge is to obtain a close enough approximation of completeness for the purposes of continuing work for the intended task, and then to obtain the incremental update since the prior inventory if needed.

The IOD design allows a full Inventory to be created with an incremental update Inventory object including a baseline Inventory by reference (see Section YYYY.3.3.2.2), thus minimizing the processing resource cost of a full Inventory. However, there is no assumption that a creating application will utilize such an approach. If it does not, the user application needs to request just an incremental update Inventory to avoid the cost of creating a full Inventory.

The Attribute Study Update DateTime (0008,041F) is intended to support obtaining an Inventory of Studies that have changed since the time of the prior Inventory. However, many repository implementations do not manage this Attribute for some (or any) of the stored Studies. Although the desired functionality would be achieved by requesting a Scope of Inventory with time range for Study Update DateTime (0008,041F) beginning at the Content Date / Time of the prior inventory, the SCP might use Study Date (0008,0020) / Study Time (0008,0030) for the matched Attribute as a fall-back when there is no available Study Update DateTime (0008,041F). There are a number of reasons this is a poor approximation. First, there is an inherent delay between the Study Date (0008,0020) / Study Time (0008,0030) (typically captured on the modality as the start of data acquisition) and the time at which that Study arrives at the repository; this delay may vary depending on the workflow of the department (e.g., cardiology studies might be sent to the enterprise repository only after reading in department, with a 1-2 day delay). Second, Studies may be updated with additional analytic or annotation Series (segmentations, presentation states, reports) well after the Study Date (0008,0020) / Study Time (0008,0030). Third, Studies received from external organizations may have Study Date / Time significantly in the past, especially for imported prior exams. Fourth, patient metadata may be updated much later than the Study Date / Time based on events totally outside the imaging department. Fifth, there may be Studies added to the repository that do not have a Study Date (0008,0020) / Study Time (0008,0030) (which are Type 2 Attributes of the General Study Module).

The user of the Inventory may need to mitigate this discrepancy by a variety of means in order to obtain an Inventory of the incremental changes to the repository. For instance, this may require adjusting the requested time range to account for typical workflow delays and reconciling differences from the prior Inventory. Some of these methods may require data and processes outside the scope of DICOM, such as using external sources (e.g., audit logs) to identify imported Studies and requesting Inventory on those (using List of UID Matching in the Scope of Inventory), or using external sources (e.g., HL7 ADT message logs) to identify changed metadata and requesting Inventory on those affected Studies.

Comparison of the Number of Study Related Series (0020,1206) and Number of Study Related Instances (0020,1208) between a prior and a current Inventory may help identify Studies that have changed content.

DICOM PS3.17 2022c - Explanatory Information