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 / solutionsRelated 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