I talk with many veterinarians who are confused about the importance of how a vendor stores images in a PACS system. Vendors add to this confusion because they make image storage the number one selling point of a system. As described in a separate article, this is probably not the number one selling point.

It is true that way your vendor stores your images is extremely important. In a recent article appearing in Aunt Minnie, Erik Ridley recommended that PACS users are wise to maintain DICOM object image integrity. The full article appears at the end of this page.

In short, Mr. Ridley very accurately points out that users should not allow a vendor to store studies in a proprietary manner unless you want to “marry” the vendor permanently. This is because if the images are stored in a proprietary manner, it may be difficult to make those studies easily available to referring physicians and other healthcare institutions; it will increase the cost of integration with other information systems, and provide fewer options for disaster recovery and business continuance.

I cannot agree with him enough and the situation is exactly the same in veterinary medicine. We are already seeing problems with compatibility issues and data migration.

Veterinarians should purchase PACS systems that store images in a vendor independent DICOM format that supports the DICOM query/retrieve service class.

Unfortunately, many (if not most**) of the PACS systems marketed to veterinarians store images in a proprietary manner. Therefore, the options veterinarians have when trying to purchase systems that store images in a vendor independent DICOM format that supports the DICOM query/retrieve service class are limited. This is unfortunate but it is a situation that we have to deal with.

Fortunately, there is a solution to this dilemma. Backing up your images off site with a company that stores your images in a vendor independent manner and maintains DICOM object integrity* will obviate the need for your PACS to store the images in a vendor independent manner. Stated another way, if you backup your images with a company that stores your images properly, it does not matter how your vendor stores your images!

By using a vendor independent archive you will accomplish three things:

• You will be backing up your data. This is something that you have to do anyway
• You will avoid the initial cost and ongoing maintenance of purchasing an in-house RAID server.
• You will have your data stored in a way that will protect you against future issues with data migration or compatibility because your backup will be vendor independent.

In order to utilize an offsite storage company your digital radiography system or PACS will be required to:

• Be able to send images to a DICOM server
• Autoroute images or utilize 3 rd party* autorouting software

*NOTE: Some of the statements contained in this article may be taken as shameless self promotion. This is because I am involved with DVMinsight.com which is a teleradiolgy and image storage company. Since we do things by the book and we do them right the first time I think I can handle the criticism. If you think I am a creep for promoting my service in this manner and you want to use someone else to backup your images, I encourage you to do so. However, please do backup your data with someone reputable. You will be glad that you did.

**NOTE: There are some unscrupulous vendors that will tell you that they store images as a DICOM file and they really don’t. Be sure to read your DICOM conformance statement. If there is a question, feel free to drop me a line and ask.

The following is Erik Ridley’s original article as it appeared on Auntminnie.com

PACS users wise to maintain DICOM object integrity
4/6/2006-www.auntminnie.com

Erik L. Ridley

Maintaining the integrity of archived DICOM objects is critical, so PACS purchasers must address the issue of data migration in the initial contract with their vendor, according to Dr. Steven Horii, clinical director of the medical informatics group at the University of Pennsylvania Medical Center (UPMC) in Philadelphia.

"Obtain a prenuptial agreement," Horii said. "A vendor must not be allowed to store studies in a proprietary lossy format unless you want to marry the vendor permanently."

He spoke during a talk at the March PACS 2006: Digital Healthcare Information and Management Systems (DHIMS) conference, held in San Antonio and sponsored by the University of Rochester School of Medicine and Dentistry.

DICOM objects are essentially the information that DICOM deals with, including images, waveforms, structured reports, and presentation states, Horii said. They consist of the header (metadata), which include patient demographics, information about the procedure and imaging system used, information about pixel data (i.e., the image), and proprietary fields used by the vendor. The object also includes the pixel data itself.

Since DICOM objects will eventually have to be migrated, it's important to maintain their integrity, Horii said. The statutory retention period of a study can be longer than the life of the storage system or media, and the effective life of a PACS network is three to six years. Studies must then be migrated to a new system, he explained.

By maintaining the integrity of DICOM studies, studies can also be made more easily available to referring physicians and other healthcare institutions, Horii said. In addition, it will reduce the cost of integration with other information systems, and provide more options for disaster recovery and business continuance, he said.

Shadow groups

One issue to be aware of is the use of DICOM shadow groups, which are intended for manufacturers and users to include material in DICOM objects that are not currently part of the standard, Horii said. Shadow groups immediately follow the standard groups in an object. For example, a shadow group of 0018 would be 0019; all DICOM standard groups have even-numbered groups, according to Horii.

The shadow groups convey the same general type of information as the standard group, and are used to place information that's needed for the equipment, but are not currently available as elements in standard groups, he said.

Manufacturers can also use the shadow groups for testing elements for eventual inclusion in standard groups, Horii said.

Shadow groups can be misused, however, when information is included in elements of shadow groups instead of the standard groups where they belong, he said.

"That's a violation of DICOM convention," Horii said. "If you've got the stuff, put it in the right place."

Vendors can also incorporate elements in shadow groups purely to put competitors at a disadvantage, a violation of the spirit of DICOM, Horii said.

And shadow groups do create a dilemma for storage systems. DICOM convention says that a conforming device does not have to interpret shadow group elements that it doesn't recognize, he said.

Including the shadow groups in storage would seem to be the most robust way to deal with them, however, according to Horii.

"As a DICOM archive, what you get is what you should give back," he said. "A storage vendor different from a DHIMS vendor would have to (store the shadow groups) if retrieved objects are to work properly."

Another option would be to remove all shadow groups before storing them, returning the objects containing only the standard groups, Horii said.

"This would cause major problems with some security systems -- those that use digital signatures and message digests," he said. "That data is computed on the entire object. If you take the shadow groups off, you're going to get a message digest or a digital signature that fails to match that computed from the original object."

Also, if the original object is stored in a different system, there would now be two different DICOM objects with the same unique identifier (UID). If the DICOM object UID was then changed, that would impact the existing database entries for the object, Horii said.

In deciding how to proceed, users should understand that shadow groups are likely to be present in many vendors' DICOM objects, he said.

"Understand how the storage system and other devices from different vendors will treat the shadow groups in these objects," he said.

DICOM integrity can be degraded when studies are stored in proprietary formats, especially proprietary lossy formats, Horii said. But, proprietary storage formats can lock you in with your current PACS vendor, he warned.

"They lock you into your current PACS vendor because it makes it very much tougher to migrate if I've got multiterabytes of stuff that's in a proprietary format," he said. "I have to convert it all back to DICOM or to another vendor's proprietary format on the way to changing vendors."

Integrity can also be degraded when information that's critical to retrieving a study is stored in the wrong DICOM field, such as when a medical record number (MRN) is placed in the comment field instead of the specified field, Horii said.

"All DHIMS clinical applications that support DICOM must support the DICOM service classes required to allow seamless transfer of studies between clinical applications," Horii said.

If the HIS or RIS has been upgraded, or if there has been a vendor change, the MRNs and patient identities need to be validated, he said. Dictionaries should also coincide to ensure consistent study descriptions.

Protecting integrity

DICOM objects can be protected by ensuring that modalities and devices support DICOM modality worklist (MWL), and by requiring vendors to complete all critical fields in the DICOM header to facilitate study migration, Horii said. All studies should be stored as DICOM Part 10 format, with no proprietary lossy formats permitted.

Institutions should also establish strict PACS purchasing standards for anything that touches the LAN or WAN, including modalities, information systems, infrastructure components, and storage and storage management components, he said.

Customers should also require that vendors, both new and old, support all necessary DICOM services classes needed to migrate data, according to Horii. This includes DICOM C-Find (archive), DICOM C-Move (archive), DICOM C-Store (archive), and DICOM query and retrieve (workstation).

The integrity of DICOM objects is critical during the initial PACS purchase, Horii said. Purchasing standards should be enforced.

Also, "purchase storage and storage management software from the storage vendor, not the PACS vendor," he said. "That helps you avoid proprietary storage problems."

Proprietary archive formats should not be accepted, Horii said.

The integrity of DICOM objects is also critical when changing PACS vendors or upgrading an existing PACS, and when consolidating storage components of isolated healthcare information systems to form an enterprise archive, he said.

By Erik L. Ridley
AuntMinnie.com staff writer
April 6, 2006