Everything you need to consider before embarking on an RF shielding project

September 09, 2022
by Lauren Dubinsky, Senior Reporter
If this is the first time you’re installing an MR unit, you might not even know what radiofrequency (RF) shielding is, and you wouldn’t be alone in that.

The average healthcare provider is often unaware that an RF shield is needed until someone tells them, according to Howard Newman, vice president of Universal Shielding Corp. A lot of his time is spent educating customers and contractors on the shield’s components and how to properly interact with it.

“We find that the customers who know where the shield is going to be installed and have contractors who know how to work with the shield have the most successful projects,” he said. “But for those that are doing this for the first time, we have no problem holding their hand and by the end of the project, they are ready to hit the ground running on the next job.”

Mike Krachon, director of marketing and sales at IMEDCO, shares similar experiences. He’s found that unless a hospital and architect have completed multiple shielding projects recently, they often don’t understand the function of the shield and the extent of the coordination required to pull the design together.

“If due diligence is completed early to select a reputable shield vendor by the team, the process is more likely to run smoother,” he added. “This is particularly true in helping the other trades understand and meet the shield requirements and the MR vendor siting requirements.”

Should you get a new or used MR unit?
Your first step is obviously to purchase the MR unit, but having to choose between the OEM and a third-party vendor isn’t so clear cut. Ben Turner, global director of RF shielding sales and operations at NELCO Worldwide, is aware that many facilities are looking for ways to save costs and may opt for a magnet from the secondary market. The downside is that you get less site planning support than if purchased from the OEM.

“A secondary supplier likely has some experience with the system they are providing but are not experts in all aspects of MR siting,” said Turner. “The contractor doesn’t know what he or she doesn’t know, and of course the client is not an expert in siting an MR.”

If you decide to purchase a used MR unit, you must understand the limitations you will face in planning for it. Turner acknowledged that the trade-off might make sense for some, but maybe not for others.

According to Newman, some of those limitations involve not having access to the magnetic shielding calculations and having to ensuring that components such as base plates, shim plates or penetration panels are delivered with the magnet. That last part is especially important if the MR is obtained from another imaging site.

Although the majority of IMEDCO customers purchase MR equipment directly from the OEM, Krachon is aware of several used equipment vendors that stand out from the rest. These vendors have their own site planning departments and can provide all the magnet’s site planning support information that is needed.

On the other hand, the sellers that don’t have access to those resources will rely on the shield vendor’s support. That means they will be taking on more responsibilities, such as passive magnetic shield modeling, and uncovering potential MR interference issues like proximity to transformers and large, moving ferrous masses.

Start the planning process off on the right foot
The next step is to decide what type of shielding your site requires. Magnetic shielding is often forgotten about in the early planning stages, and although not every site will need it, it’s still an important consideration.

If the five-gauss line is contained within the MR room or a controlled place, the site won’t need this type of shielding, according to Turner. In addition, if the magnet is centered and the room is between 18 and 20 feet wide, then magnetic shielding won’t be needed on the side walls.

“More often than not, it's the rear of the MR that is a concern for magnetic shielding,” said Turner. “If possible, the architect should try to design the equipment room to be placed behind the MR suite. That way, they control the access to that space. It’s ok, then, if five gauss is there, it’s controlled space and they’ve eliminated the need for magnetic shielding.”

He added that every site is going to need RF shielding, unless it’s incorporated into the bore of the magnet, which is typically only the case in an MR used for research purposes. An RF shield must always be a six-sided enclosure, even if your MR suite is going to be in the basement.

Once you know what type of shielding you need, you will need to develop a clear rigging plan for getting the magnet and shielding materials into the space. Newman has worked with facilities that didn’t have a plan for that and he had to make accommodations in his materials to get them through the building.

Those accommodations can involve lugging the materials up stairs instead of having an elevator. He also often must work with customers on the path of the cryogen vent inside and outside the building to ensure there aren’t any issues.

If you have an existing RF shield and plan to upgrade or replace your MR unit, the planning process will be much different. The shield must be recertified, and an RF baseline test has to be conducted to show that the shield meets the new performance levels of the equipment, or upgrade before it can be installed.

A facility may only need to replace a door or window. However, they also run the risk of having to remove some or all the interior finishes to access shield seams and check for water damage.

“There may be a point when the customer realizes that the remediation is so extensive and expensive that it would be [better] to consider a full shield replacement,” said Krachon. “An experienced shield vendor should be able to explain options and let the customer know the shield upgrade scope before any final upgrade construction schedule is set.”

Things can get even more complicated if you plan to purchase a new unit from a different MR vendor. Going with that option might require you to remove, replace or refit the penetration panel interface, cryogen waveguide, and magnet and table anchors.

Repair or replace?
Oftentimes, the state of a shield will be largely unknown until you get into the process of troubleshooting it. Turner compared testing the room to fixing a leak in a boat, in that you need to fix the biggest leak before you can find the next leak and so on and so forth.

“It’s an iterative process,” he explained. “Every site is different and it’s not black and white that you will always need a new shield if ‘x.’ Your best bet is to work with a shield vendor that you’ve done business with before, that you were happy with.”

Joel Kellogg, global director of marketing at ETS-Lindgren, said that you might only see a little bit of leakage around the penetration panel if the shield is in good shape. You might also see some leakage around the door and windows, but he assured it’s an easy fix.

“On occasion, you might end up with a room where it is leaking everywhere, providing minimal attenuation,” he said. “That starts to become an indicator that you're probably better off just replacing that shield versus trying to fix all those leaks.”

To Newman, one of the biggest culprits is water damage and it’s hard to tell the full extent of the damage on the shield. This type of damage can happen because of a hurricane flood or a sprinkler pipe bursting.

Universal Shielding Corporation’s RF panels are particle board lined with galvanized steel on both sides. If water comes into contact with the particle board, the panels may swell and cause the screws in the steel channel system to pop off, or the channel could oxidize.

“We could go out to a site and test the shield and it could be fine, but then if they had water damage, it may not be fine two or three weeks or months later,” he said. “We often tell people that you need to replace at least the parts of the shield where the water came in and where there is visible damage.”

However, if the room’s attenuation test results are very poor, he argued that it’s more cost-effective to replace the whole shield rather than taking everything apart.

According to Turner, one way to avoid water damage is to make sure that no water lines run over the RF shield in the planning and construction phase. He made the point that the risk and cost of a dripping pipe over a one-million-dollar MR isn’t worth it and that the piping can be rerouted elsewhere.

Don’t forget about the RF door
When it comes to the RF door, if the room is older than eight years, Turner recommends repairing or replacing it. He believes it’s the most important part of any shield because it must consistently make the RF seal every time it’s opened and closed.

Since technicians are traveling through these doors hundreds of times per week, Turner thinks it’s asking a lot for a door to last more than six years without any trouble. Sometimes the leakage may be caused by loosened RF panels.

“Think about the fact that technicians are bringing patients on gurneys and carts,” he said. “Bumping into the door or door frame once may not a problem but over and over will certainly cause the door to not seal properly.”

Krachon recommends getting the door serviced three to six times per year to ensure it functions as intended and remains easy for the technician to open and close. The degree of maintenance required depends on the type of door you have.

For copper finger designs, the fingers should be inspected and replaced on a regular basis. Also, the door frame should be wiped down periodically to prevent oxidation or tarnishing, which can cause friction and make it hard to open and close the door.

The newer door designs have pneumatic controls that require a compressor and lines that should be checked for air leaks that cause excessive cycling, as well as water build-up. Since double-leaf, sliding or automatic pneumatic doors are more complicated, they require even more maintenance.

IMEDCO recently introduced its new SmartSeal RF Entry systems, which feature a built-in PC that continually monitors pneumatic door operation and indication whether the door is sealed properly. It also measures air-line pressure to spot early air-line leakage, checks compressor pressure and cycling function and monitors door cycles to suggest when service is recommended.

If the systems detect any issues, an LED light illuminates above the door frame to alert staff that service is needed before the system fails. Krachon described it as a “virtual RF door service technician” that can help you avoid downtime.

Intraoperative MR
The doors are especially important when shielding an intraoperative MR (iMR) suite. A few years ago, ETS-Lindgren partnered with IMRIS and Deerfield Imaging to open a new iMR suite at a hospital in the southeastern U.S.

“Those rooms tend to be more complex, not necessarily from a shielding perspective, although there is a degree of complexity with that,” said Kellogg. “Typically, they're looking for things like sliding doors because you need this large opening to either move the magnet through or transport a patient through.”

The project involved installing three RF doors. An automatic double RF door was placed between the operating room (OR) and diagnostic room, so patients could be transferred easily to the magnet without taking up too much space in the OR.

A five-foot-wide single sliding RF door was installed in the MR control room instead of a swinging door to prevent the risk of collision. The last door was a three-foot-wide swinging door that allowed access to the iMR suite from the control room.

Magnetic fields can have a negative effect on implanted medical devices and electronic equipment such as computers, so it can’t be subjected to five gauss or higher fields. Since the floor to ceiling space below the magnet was too small, the five-gauss field had to be contained from extending into that work area.

ETS-Lindgren put M36 silicon steel underneath the slab of the floor. Many of the existing communication lines and HVAC ducts were installed lower than usual so they were far enough away from the five-gauss field.

Kellogg expects this trend of bringing imaging technologies into the OR to continue to grow. Providing neurosurgeons with these high-resolution iMR images allows them to visualize anatomy and ensure devices are placed correctly.

“That's one the area that you see a lot of activity,” said Kellogg. “There are a lot of facilities that are looking to not only have intraoperative suites where you're doing an operation and imaging at the same time, but also to check how procedures are going to make sure they’ve removed all of a tumor in real time.”