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.