Standards Watch | IHE elevates CD exchange to a new level of compatibility

The Integrating the Healthcare Enterprise joint activity by HIMSS and RSNA, which defines profiles based on standards such as DICOM and HL7, just released the new PDI (Portable Data for Imaging) integration profile as one of several supplements in their draft for trial implementation.

This integration profile specifies how images and related information can be exchanged among imaging devices using CDs. In addition, there is an invitation for vendors to participate in an RSNA demonstration. The interesting part of this demo is that attendees of RSNA 2004 will receive a sample IHE-conformant CD with sample medical images and patient information. Vendors participating as so-called IHE Integration profile Media Creator actors also will be able to generate sample CDs on site in their exhibit booths to show their capabilities to create IHE-conformant media. Vendors participating as Media Reader actors will be able to show their capabilities to import IHE-conformant media. RSNA will truly show IHE in action.

The creation of CDs for the exchange of images in a standard, DICOM manner, has been defined for many years. Initially, this was mostly used for niche applications, such as to store cardiology runs, or for cine loops from portable ultrasound. However, this application has become suddenly very popular. The reason is simple: cost reduction. If you have the images available in digital format, burning a CD costs very little, and you can easily train your file room personnel to do it. For example, a major hospital in the Dallas-Fort Worth area will gladly provide a copy of an exam for the patient to take with him or her for $85. However, if they opt for the CD option, it is free, which encourages them to use the latter option - therefore providing savings for the institution.


Writing images on CD is definitely less expensive than printing yet another film. In addition to the film and labor savings, there is another, often overlooked advantage, i.e. mailing cost. I visited with the Mayo clinic in Rochester a month ago, and they told me that they send out about 100 CDs a day. Postage for a CD mailer is less than a dollar; postage for a film jacket is about $10. They save close to $5,000 a week on shipping costs, which results in a quarter of a million dollars saved per year!

One of the risks with writing images to a CD is potential incompatibility. Imagine a patient who has traveled from his hometown, which could be thousands of miles away, to the Mayo clinic with his images on a CD, and the images cannot be viewed, or are of an unacceptable image quality because of the degradation in the storage process. The latter can happen, for example, if a chest CT image, with a very wide contrast range, is stored as an 8-bit JPEG image, basically clipping off all of the lung or bone tissue information. To prevent these situations, the DICOM standard has been very specific and limited the number of options for the images and related information to be stored in DICOM format in the form of a well-defined Application Profile, to increase the chance for interoperability.


However, what has happened over the past few years is that several of the top PACS vendors have been storing images in a proprietary format, which is unacceptable. Imagine an institution needing to have a copy of each vendor's PACS software available to read these? Ridiculous. To address this issue, most vendors package a copy of their viewer on the same CD. However, this poses two problems. First of all, any time you exchange an executable file, there is a heightened chance of spreading a virus. As a matter of fact, many institutions have very strict guidelines about installing non-validated software on their PCs. Secondly, this does not allow the proprietary images to be imported into the PACS for comparison, allowing them to be viewed using their software on their own workstation for 3D or other processing. Even if the images are claimed to be stored in a DICOM format, vendors are not always quite following the DICOM standard. There was actually a poster presentation at the recent SCAR conference in May in Vancouver from the Yonsei University Medical Center in South Korea, demonstrating how they had to validate each and every incoming CD for potential issues. Remember, once you write a CD with information that is not quite stored in a compatible way, it is out there forever.

So why is this new PDI IHE profile so significant? In the first place, the IHE definition does not only provide scenarios, or use cases, and, as is common for any integration profile, defining actors, but also re-iterates some of the common problems and issues to warn the vendors that are generating these. Some of these issues deal with the format of the filenames that are used to store them - which should be a maximum of eight characters, all uppercase, without any extensions (including the .dcm!) - the presence of a directory also known as DICOMDIR, the physical formatting following strictly the ISO 9660 Level 1, as well as re-iterating the contents of several attributes that are often not present or incorrectly encoded. In addition, this profile contains more than just a reference to the DICOM exchange standard. It also specifies how so-called Web Content can be included on the CD in a defined manner. The inclusion of this information, such as in the form of images in a web-friendly format such as JPEG, is optional, however the method to do this is very well described. The reason for including this description is because many vendors have been producing CDs containing images in this web-friendly format for patients and/or other physicians that do not necessarily have access to a viewer which can accommodate the DICOM-encoded images and other objects. This is an excellent feature, however, because previously there were no guidelines, every vendor pretty much did their own implementation and picked different file formats. In addition, it allows for storing a simple viewer software application or reports on the CD. This integration profile therefore is a means for standardizing the status quo and gives guidelines on how to include the additional non-DICOM information.


Even though the PDI integration profile looks rather simple, it has the potential to make a major impact, i.e. stop the proliferation of CDs that are potentially incompatible, have data on it that might be sub-standard and/or violate the standard agreements for physical and logical formatting. To quote David Clunie, past DICOM committee chairman at his presentation at the DICOM anniversary, "there is absolutely no legitimate reason for deliberate violations such as currently present on these CDs." Therefore, I believe that vendors need to: review current CD formatting, especially looking at the "frequently made mistakes" as specified in the IHE specification, and sign up to participate in the RSNA demo. End-users, whether current or future, must demand compliance with the new PDI profile. Remember, when you create these CDs, they will be around for a long time, and you don't want to provide your patients and/or physicians with something that has potential problems. Especially remember that if you can read a CD on a workstation from your PACS vendor, which happens to be the same as you generated the CD on, it is no guarantee that these are generated in a standard compliant format!

Herman Oosterwijk is president of OTech, a healthcare technology consulting and training firm, specializing in PACS training, see