The Right Way to Network Mobile Digital Imaging Equipment

Mobile digital imaging equipment - namely digital radiography and ultrasound - boosts patient care and efficiency by bringing imaging to the patient who often cannot travel to the imaging department or may be in a different facility than the radiologist reading the exam. But mobile imaging is not without challenges.

One of the key considerations with mobile devices is networking the solution. How will images be transmitted to the server and image review stations? "Speed is a factor," states Rick Rohde, network engineer for ThedaCare, Inc. in Appleton, Wis. The faster radiologists and clinicians review images, the sooner they can make decisions and deliver patient care. Mobility and workflow are other key considerations. How can techs efficiently transmit images acquired throughout and beyond the hospital?

Mobile device users face two major choices. They can rely on a conventional wired network or tap into wireless. A wired network is robust and offers speed and security, but wired cannot be everywhere. Some rooms may lack network drops. Wireless, while more convenient to the user, may on the other hand be more fragile and slower than its wired siblings. And the enterprise may object to sharing the wireless network with imaging because it can be a bandwidth hog. On the plus side, wireless allows users to truly image on the fly, which is the whole aim of mobile imaging devices.

Mobile & wireless: A tale of two standards

Creighton University Medical Center in Omaha, Neb., was an early adopter of GE Healthcare's Definium AMX 700 mobile digital x-ray system. The hospital had an established 802.11b wireless network prior to implementing mobile digital radiography with multiple devices running on the wireless network: voice over IP, nurse call system, bedside charting and more. In fact, before the GE project, the center ran 18 to 20 devices on each access point.

"The challenge with mobile radiography is that it takes a lot of bandwidth to transmit the images. All of these demands could overload wireless access points. We knew mobile radiography would time out other devices," explains Network Engineer Rick Sweeney. A single digital x-ray may be a hefty 10 megabytes, and each exam may include several images. The total could tax all but the hardiest wireless networks.

Obviously, the new mobile x-ray system could not override other wireless systems. Creighton University Medical Center's wireless network operates at a 2.4 gigahertz (GHz) frequency, which presented an additional challenge. The 2.4 GHz frequency allows only three channels, and the channels cannot overlap. "The access points must be scattered, so they don't overlap," explains Sweeney. Finally, 802.11b is not known for speed; it only allows 11 megabit traffic.

Sweeney and his colleagues were able to devise a solution to facilitate digital imaging traffic. "We tripled the number of access points before implementing mobile radiography," sums Sweeney. The solution is not completely straightforward. The hospital could not overlap three channels either horizontally or vertically, which created a virtual 3D jigsaw puzzle.

The access points did overlap at full power, says Sweeney. He created frequency space by powering down the access points to function at lower power and then adding the additional points for greater coverage.

Mobile radiography also has designated access points in each Creighton University Medical Center unit. That is, each unit has three wireless access points and mobile radiography is assigned to a specific point in each unit. Creighton University Medical Center also runs multiple VLANs to segment and prioritize wireless demands. For example, voice runs on one VLAN, and data runs on a second.

"If we had not added the access points, we would have had problems with mobile x-ray," says Sweeney. The additional access points did create a budget issue as they amounted to nearly $200,000. Sweeney opines, "Never assume the wireless network is complete. It's important to establish clear expectations; educate the CFO and CEO that it will require continued growth and investment. Wireless networks should be viewed as having a three to four year replacement cycle."

What about the other flavors of wireless? "802.11g solves some problems because it operates at 54 megabits," states Sweeney. The solution, however, may not be ideal. If 802.11b and 802.11g share a frequency, any wireless device running an 802.11b device will drop the access point to b speed a.k.a. 11 megabits. The upshot? "You can run 802.11b and 802.11g in the same building, but as long a 802.11b exists on your network you may not get the full benefit if 802.11g," he opines.

ThedaCare is a portable wireless digital radiography pioneer, running a Canon Medical Systems Portable DR CXDI-50G on a mobile GE AMX-4 on a wireless hospital network. Wireless came first; the hospital installed an 802.11b network in 2002. The hospital opted for the wireless portable option because not all rooms are equipped with network ports. "It's also a workflow issue," says Rohde. Forcing techs to return to a network port to transmit images can disrupt workflow.The hospital employed a unique solution for its portable x-ray and ultrasound equipment. "The wireless technology is completely separate from the diagnostic equipment. The devices don't know that they are wireless. We removed the hard wire from their network port and connected each device to a wireless bridge [access point] on the mobile cart," says Rohde. Each diagnostic device has an IP address compatible with the network. Another plus of this approach is that it removes modality vendors from the equation; the same model can be used across devices and vendors. The solution, however, does not solve all wireless challenges. Speed of the 802.11b network limited the utility of portable x-ray at ThedaCare.

When the hospital first rolled out wireless portable imaging on 802.11b, transfers from the imaging device to the PACS archive took approximately one minute. A recent upgrade of all access points to 802.11g provided additional speed. Now image transfer is an impressive 20 seconds, and the portable imaging devices can be plugged into the network for faster transfers.

Rohde's advice for his peers is simple. "Do the entire wireless survey upfront, and install wireless as part of a master plan. It's not necessary to complete the entire campus at once, but it is important to have a plan."

The Ohio State University Medical Center in Columbus is another wireless portable ultrasound pioneer. The center has paired GE Healthcare's LogiqBook portable ultrasound system with wireless transmission since 2002 and aims to develop a model for full enterprise transmission. "The 21st century ultrasound paradigm pairs one machine that travels to the patient bedside with multiple operators and viewers. Wireless ultrasound enables this model," explains David Bahner, MD, director of ultrasound.

The center has addressed the speed issue with a robust wireless backbone. The medical center is plastered with access points that operate at all three wireless frequencies - 802.11a, 802.11b and 802.11g and has achieved three- to nine-second transmission from the LogiqBook to PACS. "[Healthcare] Sites need high-end bandwidth to transmit images. Having all three frequencies is important," opines Bahner.

Despite the success on the speed front, technical challenges remain. It's no surprise that security rears its head. After relying on WEP (wired equivalent privacy) as a first security measure, the medical center implemented EAP (extensible authentication protocol). "This is a good second step, but it is not the ultimate solution," notes Bahner. EAP-FAST will be another improvement, but Bahner believes tying security to authentication could solve multiple challenges. How does it work? Biometrics or radiofrequency identification could link exams to credentialed users for security, billing, QA and more.

Staying tethered

Despite all of the talk about wireless, it is still quite possible - and perhaps more common - to run portable equipment with a wired network. Novato Community Hospital in San Francisco operates its Philips Medical Systems PCR Eleva portable digital x-ray systems on a wired network.

PACS Administrator Gary Woodruff summarizes the challenges of portable imaging. "Traditionally, you want to plug the digital imaging device into the network, but the hospital may not have a network in the ICU or patient rooms." The solution is to download images from the computed radiography unit, so that the hospital does not have to rely on a network drop or wireless.

At Novato Community Hospital, techs simply remove the CR plate and take it to the main radiology department for processing. Images are transferred via a network drop located next to the battery charger for the portable units. The parking station is a handy one-stop shopping solution. Techs return to the station to retrieve worklists and download images. Multiple options are important, and Novato Community Hospital did wire its ICU units, enabling techs to plug into a bedside port for portable x-ray and ultrasound image transmission.

Northport Medical Center in Northport, Ala., relies on a similar model for its SonoSite Titan handheld ultrasound solution. Portable ultrasound studies are automatically transmitted to PACS via a network drop in the ultrasound suite.

Novato Community Hospital relies on a slightly different model in its OR suites. Once the tech exposes the CR plate, she identifies the plate to the Eleva processing system and the images are displayed on the viewer in the OR. "This process avoids the webserver, which can take four to five minutes. This model displays images in 20 to 30 seconds," says Woodruff.

Going wireless with portable ultrasound

Mercy Hospital and Medical Center in Chicago turned to Zonare's ultrasound system when it recently opened an offsite ultrasound facility. The system provides flexibility by converting from a full-featured, cart-based system to a high-resolution compact unit, says Peter Jabeck, administrative director of radiology.

The hospital currently uses three systems internally and at three offsite centers. Two sites are connected to the main hospital campus via T1 lines. At two offsite centers, all ultrasound exams are completed in a designated room with a network drop, facilitating immediate transmission from the scanner to the hospital. At the other facility, users remove the scan engine or the compact Flash to download images to PACS.

Jabeck aims to build on the successful outpatient model with a fourth ultrasound for ER and enterprise use. The plan is to use the portable system to complete scans in patient rooms and automatically download images to PACS at designated PACS ports throughout the enterprise.

Portable imaging beyond the enterprise

Not all portable imaging takes place within the walls of a single healthcare facility. When images need to be taken outside of the network, it gets more challenging still. "There were no particular challenges adapting portable ultrasound to our network and subnet. The challenge is getting studies acquired at clinics outside of our network," says Frank Harty, information systems director for Heart Clinics Northwest in Spokane, Wash. Heart Clinics relies on eight Siemens Medical Solutions Acuson Cypress systems for portable cardiovascular ultrasound.

Internal image transfer is a snap; the Cypress system can send images from the ultrasound suite to multiple viewing stations accurately and quickly. When images are sent to referring physicians, the clinic completes a file transfer or sends a CD via sneaker net.

"When we take the unit to one of our 20 outlying clinics, we can't send images back to the main clinic because the other clinics are on a different subnet," explains Harty.

The solution is to use a computer as an intermediary. When portable ultrasound exams are completed at offsite clinics, the images are sent to a computer at that location. Then the file is sent to the main clinic. Harty wrote a program to poll PCs at outlying clinics to grab data from all the ultrasound systems as the data become available; the program makes data available to all physicians on the network and automatically moves the data into the patient's EMR.

While Heart Clinics has eight portable Cypress systems, the units are not very mobile internally. "We try to schedule patients in the rooms where the systems are located as much as possible." says Harty. One reason for this approach is that each system can be configured to handle only five different network locations. Consequently, each machine has five designated sites.


There are multiple ways to tackle the big picture and the details when it comes to mobile image networking. It may make sense to add network drops, bolster the wireless network or configure a unique internal solution. The end result in all cases is enhanced service for physicians and patients on multiple levels.