DICOM gray-scale standard seeks to impose consistent image quality

April 17, 2002

Customer demand will drive spread of GSDFGray-scale standard display function (GSDF) for DICOM has been struggling to achieve critical mass ever since Integrating the Healthcare Enterprise (IHE) began defining a profile for

Customer demand will drive spread of GSDF

Gray-scale standard display function (GSDF) for DICOM has been struggling to achieve critical mass ever since Integrating the Healthcare Enterprise (IHE) began defining a profile for consistent image presentation soft-copy/hard-copy in Year 2. A recent study published by the University of Texas MD Anderson Cancer Center found that GSDF still has a ways to go. It will probably get there before the end of this year‹either on its own or in conjunction with GSPS, the gray-scale soft-copy presentation state. Vendors are already making preparations.

"By the next RSNA meeting, we expect to introduce full support for GSDF and GSPS," said Rik Primo, division manager of clinical networking/PACS at Siemens Medical Solutions USA. "We've done a lot of work already within the IHE framework and hope that by then we will be able to refine our algorithms and code."

PACS vendors agree that GSDF holds promise. The concept behind the standard is to provide the basis for achieving a consistent gray-scale image and display data (including annotations), regardless of whether the image is viewed in hard copy, on a PACS workstation, or on a PC. This capability, however, depends on the image containing the proper P-values (presentation values), which can then be interpreted by the PACS or the displaying workstation using a DICOM presentation look-up table (LUT). The success of GSDF doesn't depend only on the PACS, however.

"To really start benefiting end users, the onus is on the modality vendors to provide image acquisition with P-values," said Allan Noordvyk, director of systems analysis and user interface design for ALI Technologies. "From a PACS point of view, it's better to use GSDF for everything. All parties involved in the data transfer, including the acquisition device and HIS/RIS, have to implement the optional parts of the standard in order for everything to work."

Part of the problem is that vendors were required to support the presentation state before it was well defined in the DICOM standard, according to Primo. While the current Sienet PACS version does support GSDF, it has only limited support for GSPS, because Siemens, like many vendors, created proprietary DICOM tags before the public tags became available. DeJarnette, for example, has implemented GSDF in some products (LaserShare, ImageShare CR, and VisiShare) but has up to this point used the Barten Model as its baseline for gray scale.

"When DICOM came out with the gray-scale standard, they used the Barten Model as a definition," said Mike Galusa, DeJarnette vice president of research and development. "They wanted to have a gray scale that was based not on luminance alone but also on perceived differences.

Release schedules can slow implementation of standards like GSDF, according to Alan Orth, vice president of marketing for DeJarnette. Robert Horn, research scientist on Agfa's technical development staff, concurs.

"Some of the delay is due to lead times on development cycles‹it takes a while to get the standards in," Horn said. "The forcing function has been the IHE coming up with a consistent way to present images. If everyone does it this way, the recipients and the transmitters will agree and demonstrate that it works."

GSDF is­so far­more theoretical than practical in part because customers simply haven't asked for it. Until GSDF or GSPS becomes an everyday part of RFPs, there's no real urgency for imaging vendors to show that functionality, no matter how potentially useful or cool it may be.

"Currently, our ProVision PACS supports GSDF, and we've had that capability for several years," said Louis Humphrey, product manager for ProVision PACS at Cerner. "To date, having GSDF has not been a big issue, but I think that is changing."

The whiff of change is reflected in product planning. GSDF support is pending for some DeJarnette products; ALI will showcase its new products (scheduled for release in 2003) that implement the GSPS framework at RSNA, and Agfa plans to support GSDF/GSPS in its new product releases. Several products from GE Medical Systems, namely the Centricity RA 600 and the PathSpeed CR, already support GSDF, according to Claude Benchimol, vice president of global technology.

"DICOM GSDF is viewed as a strategic standard for GE Medical Systems because it will have direct impact on our customers and service organization," Benchimol said.

Studies such as the one by the MD Anderson Cancer Center will help raise customer awareness, as will IHE demonstrations. RSNA and the Healthcare Information and Management Systems Society, as well as other industry groups, will also help. The American Association of Physicists in Medicine (AAPM) formed Task Group 18 to evaluate performance of electronic display devices. At the association's meeting in Montreal in July, the AAPM and PACS and DICOM consulting firm OTech plans to host a hands-on workshop that will cover consistent reproduction of gray scale using GSDF and the image reproduction guidelines being developed by Task Group 18. Herman Oosterwijk, president of Otech, hopes the workshop will be attended by a cross-section of the imaging industry.

"Printer vendors seem to know the image quality issues, since they get calls all the time that the images don't look the same," he said. "It seems like the image acquisition vendors are less knowledgeable about the problem."