With filmless radiography, acquisition and quality of the image are very important. These aspects of digital imaging were our primary considerations in the first two articles in this series. Digital radiography actually entails two additional features of the system: storage and viewing. Unless storage and viewing are fully evaluated, the entire system will fall short of expectations, regardless of image quality.

Picture Archiving and Communication Systems
Simply stated, the PACS is the PC/server and software component for storage and retrieval and, ultimately, viewing. In veterinary medicine, many types of PACSs are available. The simplest PACS supports a single PC/laptop workstation (typically located at the acquisition point-the x-ray table) and manages one imaging modality (for example, the x-ray). More sophisticated systems support networking through both Intranet and Internet access, allowing for secure, unlimited viewing (copies); these advanced PACSs also support multiple acquisition and display modalities (such as ultrasonography, MRI, and CT). Obviously, a PACS that only supports one workstation is tremendously limited, and creates problems in sharing when more than one person needs to view the data (e.g., clients, viewing during surgery). Being limited to only one modality causes similar limitations and may result in redundancy (i.e., separate PACSs) if another system, such as ultrasonography, is added. Finally, the images displayed via the PACS must all look the same to all viewers.

Digital Imaging and Communication in Medicine
The concerns surrounding the limitations of veterinary PACSs have already been addressed in human medicine. Propriety software limited the ability to share and integrate information, and systems did not always meet standards for securing the integrity of medical data. Each vendor had a different, proprietary image format and messaging protocol, so the various systems could not communicate with one another. In response to these concerns, the American College of Radiology and the National Electronics Manufacturers Association developed a system of standards, known as the DICOM protocol. All recently designed imaging and PACS systems for human medicine must adhere to these standards.

In addition, DICOM enhances image security: each image is assigned a unique marker that creates a traceable record to the machine of origin, and the original raw image cannot be modified. DICOM also enables users to avoid being "locked" into one vendor's product and even supports Macintosh computers. A system that meets the DICOM standard ensures that images can be viewed on any computer through use of readily available software that supports DICOM viewing, thus giving the practice options in selecting viewing software. A DICOM compliance statement is particularly valuable if you are considering future equipment purchases or are already working with an advanced imaging system in providing ultrasonography services. The compliance statement gives assurance that the systems will "speak the same language" and that storage and viewing will be seamless.

To this point, veterinary medicine has not adopted a standard for digital imaging systems. The American College of Veterinary Radiology is currently working on recommendations; the author assumes that DICOM will play a major role in the standards set forth. Regardless, one can be certain that if he or she owns a DICOM-compliant system, it will meet or exceed any minimum standard that will be established.

Open Format
One of the key strengths of DICOM is the issue of open format-many veterinarians are interested in integrating digital images into practice management software. In human medicine, imaging centers and hospitals require a seamless interface between PACS and the Hospital Information System and Radiology Information System. In veterinary medicine, the approach thus far has simply led to oversimplified software, which is cumbersome at best. The software is proprietary, meaning that you have to buy the vendor's practice management software as well as a PACS to achieve connectivity. Some PACSs are also proprietary and thus are unlikely to be compatible with your practice management software, unless the PACS and the software are developed by the same vendor. It is incumbent upon software vendors to design programs that can communicate with all systems; following DICOM principles could facilitate this process.

The primary benefits of integration are as follows:
• Storage of images: Because DICOM images can be as big as 13 megabytes, it is advantageous to have the files supported on a separate server, or even stored off-site, but readily retrievable. Having to keep files of this size on the veterinary practice computer could have negative effects on performance.
• Billing and tracking services: Full integration with systems that can create a list of charges according to products and services (very similar to how many systems support reference laboratory services) will be very valuable in ensuring that proper fees are charged and reducing inputting errors.
• Seamless functionality: The more steps involved in a process, the less likely we are to take advantage of it. Most of us simply want to push a button and let the computer do the work!

Because filmless systems are relatively new to veterinary medicine, open format programs are still limited. Currently, there is a limited number of veterinary practice management software systems that fully integrate with PACS and read DICOM; it appears that in time more will follow.

Reliability
Digital radiography causes dependence on the computer system. Reliability and support of the system are critical in making a purchasing decision. Radiology services are a significant component of most veterinary practices, thus the quality and performance of these systems are of utmost importance. Purchasers must thoroughly explore the available systems and how they perform. Redundant features must be built into the system to prevent loss of data, and it should require minimal maintenance. The reputation of the manufacturer and the level of service that will be provided after the sale must also be investigated. Remember: It's a dangerous practice to assume that all systems are created equal-do your homework, ask questions, and visit practices using the systems in which you are interested. The system's advantages and disadvantages are best demonstrated in real-life situations.

Summary
PACS and DICOM are standards developed for human medicine that could guide the veterinary profession in protecting users of imaging systems. These standards allay legal concerns, ensure compatibility with other systems, and allow freedom to make purchasing decisions that are not vendor-restrictive. Although discussions of digital radiography often center on image quality, storage and viewing features are equally important considerations; the storage and viewing software must be robust, flexible, and reliable.