Services for Advanced Image Access

1. 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

2. 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

3. 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

4. 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

5. 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?

6. 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