PDI Extensions - Detailed Proposal
1. Proposed Workitem: PDI Extensions
- Proposal Editor: David Clunie
- Profile Editor: David Clunie
- Date: 2008-10-01
- Domain: Radiology (Mammo, NM), Cardiology, Radiation Oncology
PDI uses uncompressed CDs and these are too small for many studies without awkward disk spanning.
DVD and USB media are already supported in DICOM, demonstrated to be interoperable, and reading and writing hardware is ubiquitous. Lossless and lossy compression are also supported by DICOM.
Vendors are already attempting to satisfy the demands of users by producing DICOM but not IHE PDI compliant media using compression and larger media.
2. The Problem
The existing IHE PDI profile supports CDs only, and does not use compression (lossless or lossy) for radiology images. Modern acquisition techniques often produce single data sets that exceed the available PDI CD capacity, and disk spanning (using multiple CDs for one study) makes them difficult (and slow) to view.
The lack of support by IHE of existing standards for contemporary hardware, larger media of low cost and effective compression schemes creates a "credibility gap" for PDI.
Increasing attention on image sharing and media interoperability demands that PDI make use of contemporary rather than obsolete technology to satisfy users demands.
3. Key Use Cases
A multi-detector CT, or a PET-CT scanner produces a large high resolution set of images, which needs to be sent off site to a referring physician for review on their own PC or importation into another site's PACS. The size of the image set exceeds the capacity of a single CD but would fit on DVD media, with or without lossless compression.
Without importation (which may be slow), the alternative of spanning CDs makes it impossible to view the study in its entirety using the on-board or a pre-installed viewer.
For referral to another facility for consultation or treatment, a set of relevant studies for a patient need to be recorded on media. The total size of the studies exceeds the capacity of a single CD.
An ambulatory patient receives successive imaging studies at external imaging center for review by the referring physician, e.g., to monitor the progress of treatment, and the referring physician needs to review the entire set simultaneously from a single piece of media since they have no persistent local storage. Updating a previously finalized CD is difficult if not impossible, but USB memory devices permit the possibility of adding to an existing record.
A referring physician has a finite, usually short, period of time in which to review images, and delay reduces their productivity and effectiveness. The use of higher capacity DVD media, compression to reduce the size of what needs to be read from mechanically slow disks, and memory based media all reduce the time required to review images.
A referring physician, such as a specialist neurosurgeon, orthopedic surgeon or pulmonologist, bases their decision to manage their patient on their own interpretation of the images, irrespective of the radiologist's interpretation expressed in the report. As such they require and demand a full set of diagnostic quality images without lossy compression. However, the total size of the set of images sometimes exceeds the capacity of the CD media, and the imaging center routinely lossy compresses the images, or compresses excessively, after the radiologist has interpreted them, leading to an incorrect interpretation by the referring physician and an unfortunate outcome for the patient.
4. Standards & Systems
DICOM already supports larger (DVD) and faster (USB memory) media already, and provides for both lossless and lossy compression as clinically appropriate. Fears of lack of DVD interoperability have been allayed by successful media readability tests performed at the 2008 IHE NA Connectathon.
No PC in recent history has been shipped without both DVD drives and USB connectors.
5. Technical Approach
PDI can easily be extended to support DVD and USB with minimal changes by adding the relevant DICOM Media Application Profiles to PDI.
DICOM contains a family of "General Purpose DVD with Compression Interchange Profiles", which support any of the 120 mm DVD media other than DVD-RAM, including DVD-R, DVD+R, DVD-RW, and DVD+RW. DICOM also contains "General Purpose USB and Flash Memory with Compression Interchange Profiles". There are separate profiles for support of either JPEG lossy and lossless compression, or JPEG 2000 lossy and lossless compression.
IHE could, if perceived as important for interoperability, forbid the use of compression by constraining one of these profiles.
It is currently proposed that DVD and USB be added as separate options to the existing PDI profile, without any phased introduction.
It is also proposed that JPEG compression be supported in this phase, and that JPEG 2000 be deferred to a later phase, due to lack of widespread adoption, its complexity, and questions as to its benefit for certain types of large images (especially CT).
In a future phase, it might be desirable to also add the MPEG DVD profile, but this has little application in the radiology domain and there is little experience with respect to its interoperability, so it is proposed that this be deferred for now.
- Portable Media Creator
- Portable Media Importer
- Image Display
- Report Reader
- Print Composer
- Display (ITI TF)
- [RAD-47] Distribute Imaging Information on Media
New transactions (standards used)
Impact on existing integration profiles
- Add a DVD option to PDI
- Add a USB option to PDI
New integration profiles needed
Breakdown of tasks that need to be accomplished
- Agree on whether or not both DVD and USB are required
- Agree on whether or not to include compression
- Agree on which compression scheme to support (JPEG or JPEG 2000 or both)
- Harmonize with requirements of cardiology domain
- Harmonize with requirements of any other domain that uses DICOM (eye care, radiation oncology)
- Agree on whether or not to harmonize with the XDM profile of the IT domain
6. Support & Resources
Given the very low effort from the technical committee required, since all the work has already been done in DICOM, a single editor should suffice and is committed.
As detailed in the proposal for Basic Image Review, many referring physician groups have emphasized their strong "support" (demand) for reliable, fast, interoperable media.
In Australia in particular, experiments with USB media to replace CD are well under way.
In Germany, the DRG certification already permits the use of compression on CD using the DVD profile (contrary to existing PDI recommendations).
- Political risks
- not proceeding with this proposal would upset many !
- adding support for lossy compression may be perceived as "endorsing" its use
- referring physicians require and demand diagnostic quality images
- Technical risks:
- interoperability of DVD hardware - mitigated by results of connectathon experiments
- interoperability of USB hardware - unlikely
- capacity limits of USB versus filesystem - DICOM needs support for FAT32 not just FAT16
- interoperability of compression schemes
- danger of proliferation of too many schemes (JPEG and JPEG 2000)
- lack of (and cost of) support for JPEG 2000
- real or perceived limits of JPEG lossless (not as effective as lossless JPEG 2000)
- real or perceived limits of JPEG lossy (image quality, 12 bit maximum)
- risk to viewer/importer support of very large datasets (exceed RAM or OS)
8. Open Issues
- compression or not
- choice of compression
- possible need for privacy and security solution - encrypted media ???
- MPEG or not ?
- DICOM CP to retrofit compression to CD ?
9. Tech Cmte Evaluation
Effort Evaluation (as a % of Tech Cmte Bandwidth):
Responses to Issues:
- leave it out if contentious
- David Clunie