Services for Advanced Image Access CP 309 and Advanced Query/Retrieve Work Item WG-04, 18 February 2003 Harry Solomon and Yongjian Bao GE Medical Systems

Drivers / Use Cases Lossy compression for long-term archive –Compression requires new SOP Instance UID –How to access images based on original (uncompressed) UID? Multiframe images (XA, US, now MR, soon CT) –SR may reference single frames –How to access receiver-specified individual frames without retrieving entire Multiframe SOP Instance? Large pixel matrix images –Secondary review does not need high resolution –How to access images with a receiver-specified maximum matrix size? Bandwidth constrained networks –Teleradiology workstations need image access –How to access images with a receiver-specified compression? Related but separable issues / solutions

Lossy compression for archive Uncompressed images are used in the routine workflow, and references to those images are produced and distributed across a variety of products (objects, databases) For long term archive, images may be lossy compressed, and the uncompressed images deleted DICOM requires such lossy images to have new SOP Instance UIDs –A valid requirement for safety – not the same object seen in diagnosis –Lossy compression attributes must be added to the object An application will not be able to retrieve a referenced image (which has been deleted), and currently has no way to obtain the UID of the lossy compressed copy

CP 309 Proposal Adds “Alternate Representation Sequence” to Instance-level Query –Allows reference from original image to lossy compressed, and vice versa –Requires no new services Allows Query SCP to return Instance Availability value “Unavailable” Query SCU can decide to retrieve (or not retrieve) the alternate image –I.e., C-MOVE does not transform retrieve of original UID into a retrieve of lossy object Compression is determined solely by the storage system (at storage time), not the query user (at retrieve time) –Storage system may uncompress to a supported transfer syntax on retrieval Open issues –Should the Alternate Representation Sequence include attributes such as storage compression syntax and quality? –A special case to be considered is the Storage Commitment interaction with an archive that receives the uncompressed image, but only wants to commit to storing a lossy compressed version

Advanced Query/Retrieve Work Item Deals with user-specified constraints on format of retrieved data Some possible overlap with CP309 –Image storage system could store multiple compressions of images (persistently or virtually), and could allow user system to select from Alternate Representation instances Intent of Work Item is for retrieve time specification of arbitrary format parameters –Probably requires new Query service Issue: –Is there any reason to combine CP309 with Advanced Query/Retrieve Work Item? –Are they distinct enough to allow parallel development? –Does WG4 have any input on CP309?

Observations on Advanced Q/R Retrieve ready for display (no further image processing) should be out of scope –Being addressed by joint ISO/DICOM WADO initiative (Web Access to Persistent DICOM Objects) Allows specification of frame and matrix size –Scope must be retrieval to a DICOM application for further image processing Creation of a temporary SOP Instance created for specific query is probably not a good solution –How to treat persistence of that temporary object? –Interactive access to large objects (e.g., MR) will create thousands of mini-instances to be managed –Alternative – return pixel (and other) attributes in response of new Query service, rather that trying to reuse Retrieve service New Query service is needed anyway