RF shielding considerations in the MR suite
September 15, 2021
by John R. Fischer
, Senior Reporter
It is a common misconception among some imaging providers that an existing radiofrequency (RF) shield can easily be converted or modified to work with any new MR system. Experts in the shielding industry say this could not be further from the truth.
Whether it be a new installation or repair of an existing shield, information pertaining to the schematics of the room, to who the magnet vendor is, is necessary to help shielding vendors and planners understand the present shield and site conditions and the best way to proceed for the specifications on the incoming unit.
"Understanding their situation is important for us because it enables us to provide the information they will need to convert the existing shield and help walk them through normal timelines and milestones, so their expectations are understood and more importantly, reasonable," Mike Krachon, director of marketing and sales for IMEDCO, told HCB News.
To help facilities maximize shielding performance, HCB News has put together a guide for addressing potential issues that often arise around this technology.
Radiofrequency shielding requires advanced planning and providers must be ready to supply the shielding manufacturer with any information they need. This includes, but is not limited to schematics of the MR room, contact information for the magnet vendor and equipment supplier, what type of MR system is being installed, if the provider can install the shield itself, budgeting information, and if the project has any unique requirements.
The first question that Cristiano Villa, president of Istra Corp., likes to ask is where the RF shield will be located. “It is not just about what is currently nearby but what may be nearby during the planned life of the MR. Does the building owner plan to lease the adjoining space to a data center or will the lower floor become a warehouse with forklifts driving nearby during the day?”
Other factors to consider when determining the location of the shield are high voltage sources nearby; moving metal contraptions, such as cars and elevators; and magnetic fields generated by MR scanners. Additionally, it is important to identify any features or products that will be included in the MR room.
“If you plan a basic scan room, a basic RF shield is adequate,” said Jim Maslowski, president of PDC Facilities. “However, if you plan to add patient experience products, it's best to purchase everything from the shielding company to ensure single-source responsibility for compliance with RF and EMI requirements.”
With any RF shield installation or repair, providers should know how old the RF shield is and if the new shield is identical to the existing one, according to Walter Bernschneider, sales manager of MRI-Systems. Costs and timelines for shielding projects are also important to address in the beginning, starting with the consultations right through to the installation itself.
The emergence of stronger and bigger scanners, as well as compact and mobile ones, has also affected installations, according to Jean Michel (JM) Paré, director of marketing and business development at SDI Canada.
“For bigger scanners such as 7T MRs, the room needs to be bigger, which represents challenges for the MR suite's location,” he said. “This increases the need for a magnetic shield to ensure safety around the MR area. Also, because of the increase in size and weight of the magnet, structural capacity of the building and delivery path can be critical. On the other hand, compact and mobile scanners will require a different approach as access and configuration of the room will be more critical.”
Replace vs. repair
As shields age, wear and tear will take their toll. Determining if a shield can be repaired or needs replacing starts with an RF test, says Joel Kellog, marketing communications for ETS-Lindgren.
“In many cases, the performance will have degraded a bit due to lack of maintenance of items like doors. In these cases, it can be quickly determined that the room could be reused,” he said. “However, in some cases the rooms may have suffered significant degradation in performance and it may be difficult to identify the root cause, as so much of the shield is covered by interior finishes. In these cases, it may be more advantageous to simply replace the shielding.”
An RF test should be performed every three-to-five years to assess current performance and detect any unnoticed damage such as leaks. Shields may be prone to water damage such as from leaky pipes, roofs and unexpected flooding in, around or over the MR suite.
Lack of maintenance or abuse of the RF entry doors is also a common problem, according to the experts. Items or options added after the shield was originally installed can also compromise the RF integrity and require repair.
After the test is completed, a recommendation is made concerning what remediation, outside the anticipated new magnet component configurations, may be required. It may not always be possible to make such adjustments without describing a number of contingencies, since correcting all RF compromises at the same time is often prohibitive. Some remediation may require several iterations if a single compromise, such as a severely leaking door, may mask others.
“These scenarios are what add risk to the accuracy of the costs of shield modifications and the required time to have the shield ready for the new MR,” said Krachon. “Working with a shield vendor that will provide a realistic estimate and identify the associated risks will help you weigh the cost of these repairs against the cost of replacement.”
This is especially true when bringing in a new MR system or a magnet from a different vendor. In such cases, it is almost always best to replace the shield, says Villa. “Each MR has different requirements for items including electrical panels, quench pipe and magnetic shielding.”
Keep an eye on the door
The most common culprit of shielding damage is the door, as it is the only moving part of the shield. While simple to maintain, providers often neglect this component, which, over time, is worn down by constantly being opened and closed.
“Doors do require periodic cleaning, adjustment and gasket replacement to maintain the specified performance,” said Matt Boesel, division manager of RF Shielding at PDC Facilities. “If the door has an automatic feature that uses compressed air, the air delivery system will require periodic preventive maintenance.”
Door compressors can be maintained by checking for water content and double-checking lines. It also is best to avoid bumping objects into the door and its frame such as transporters and tables, as these can create dents that can alter positioning and disrupt performance. If not carefully maintained, doors are often unsalvageable and will need to be replaced, along with the frame at times. It also is wise to check any windows in the room to see if they have incurred any damage.
Recapping key points
Knowing what goes into any shielding project starts with consulting shielding vendors and using their expertise, especially when installing or repairing a shield for the first time, according to Krachon. "I can only encourage people, when they realize there is an MR upgrade or addition as part of a project that is in the planning stages, to get involved with one or two experienced shield suppliers right away and use them as a resource, so the right questions and information can be given to the entire design team and an accurate scope can be identified for everyone. This will go a long way to set the correct expectations regarding scheduling and pricing, and also to understand the risks.”
Determining whether to replace or repair a shield comes down to many factors. But it ultimately starts with an RF test. “If the test indicates that the room is not performing to specification, but the location of the RF leaks can be identified, the majority of the time the RF shielding is repaired and reused. If the leaks cannot be located or the repair cost is too high, a new RF shield installation is advisable,” said Boesel.
It is also necessary to maintain the shield in its entirety, especially the door. More so, providers should have a thorough understanding of what product they are buying and what is required for its installation.
“Maintaining the RF seals and cleaning those surfaces can help maintain the performance of the room,” said Kellog. “Additionally, maintaining supervision or control over things that are added to the MR suite can help protect the shielding as well. Far too often an item is added to a room without considering how to maintain the RF integrity of the room.”
Paré, of SDI Canada, says other important things to keep in mind are communication between the shielding manufacturer and other partners on the MR design team, and to involve the shielding company early. “The sooner the shielding vendor is involved in the planification of the project, the easier it is to prevent extra costs and changes during construction. Any good shielding vendors will work diligently with the planning and design team during design phase and the contractors during construction phase. Always feel free to ask for their help, as this will benefit every stakeholder in an MR project.”
At the end of the day, all providers should keep in mind that a well-kept and maintained shield helps prevent delays that pose harm to patient care, prevents the need for costly repairs or replacements and with the right maintenance, can be used throughout its entire expected lifetime.
“Today, with the emphasis on MR workflow optimization and patient experience, the RF shield and its RF filtering technology are increasingly important in the design process,” said PDC Facilities’ Maslowski.