One of the great things about an MR scanner is that once it’s installed, it shouldn’t be going anywhere anytime soon. That’s fortunate, considering the complicated logistics that go with getting it there in the first place.
But eventually, after many years of use, you may find yourself back in the market for a replacement scanner. When that time comes, one of the first steps should be testing the radiofrequency (RF) shield, an out-of-sight and easily forgotten barrier that allows the system to operate.
“Just because a shield that’s been there for 10 years has not created a problem for a five or ten-year-old magnet does not mean it’s still performing as it had to on day one, for many reasons,” Mike Krachon, director of sales and marketing for IMEDCO America, told HCB News. “The predominant requisite of replacing any equipment is to show the shield that has been there looks like it just came out of the box.”
The most obvious sign that a shield is not attenuating correctly is when artifacts appear on the MR scans. (Photo courtesy of NELCO Worldwide)
If the shield is not operating to spec at that time, and the vast majority won’t be, then a shielding specialist will be required to get the shield to the point where it meets new equipment performance limits. Along with Krachon, HCB News sat down with a number of shielding experts to discuss the ins and outs of these vital structures, and how providers can ensure any work on them goes quickly and smoothly.
Be ready with answers
The first thing a shielding expert will need to know before evaluating an existing shield, or partnering with you on a new shield, is the make and model of your scanner. They will also want to know about the other technology being used in the MR suite, and any information you can provide concerning the site layout will also be helpful, such as construction blueprints.
“Foremost we ask for the site drawings, and if available, a complete site audit,” said Cristiano Villa, president of Istra Corporation. “Understanding the spectrum of electromagnetic interference (EMI) and RF that can affect the MR allows us to help the customer make educated decisions and address any issue before construction begins. We also inquire about future construction plans for the facility and the area.”
Since RF shields must line every inch of the room, including the floors and ceilings, spatial considerations must be comprehensive. It’s also critical, to shielding professionals as well as MR vendors, that the floors be absolutely level.
“If the owner is doing this for the first time, they have to make sure they have a path for the magnet entry and have to understand how the magnet is being transported in the building,” said Howard Newman, vice president for Universal Shielding. “They also have to make sure they understand how our shielding components get transported into the building.”
Consulting directly with the MR vendor is a good way to obtain shielding support and information. In most cases, they should be able to provide site planning documents and details on the right shields for a given scanner and how to transport components. Many of them also have shielding specialists they can refer you to.
For new installations, it’s best to get the shielding expert involved in the planning process sooner than later, advises Walter Bernschneider, sales manager for MR systems with Albatross Projects.
“RF shielding is a necessary evil for every MR system and clients do not always understand that,” he said. “Therefore, a very early involvement of the RF shielding vendor is one of my first wishes. The second very important wish is to ensure a comparison of the different materials for RF shielding, because that determines pricing both in the short-term and long-term. Not every cheap solution is later a cheap solution.”
To replace or repair
The RF door is the part of the shield that is most prone to wear and tear due to it being a moving part, and should regularly undergo routine maintenance. (Photo courtesy of Universal Shielding)
The most obvious sign that a shield is not attenuating correctly is artifacts on the MR scans. This can be caused by a variety of issues, such as a breach in the RF structure or water damage from a leaky roof or pipe. Getting to the bottom of what’s causing the artifacts is key to determining whether a shield needs to be replaced or can be repaired.
“If they have a history of artifacts on their scans and have frequent calls to service the RF shield, it’s a good indicator that regardless of how old the shield is, you want to replace it when the customer gets a new magnet,” said Jim Maslowski, president of PDC Facilities. “Perhaps the shield was not installed properly in the beginning; or maybe it’s affected by moisture, which will cause oxidation and corrosion. Oxidation and corrosion will reduce the useful life of the RF shield and eventually cause a breach in the shielding, which will allow RF interference into the scan room.”
Repairs and replacements can often be avoided through routine maintenance. This is primarily for the RF door, which is especially important because it is the only moving part of the shield and is most prone to wear and tear.
"You're going to open and close the RF door hundreds, maybe thousands of times in a week", said Ben Turner, global director for RF shielding at NELCO Worldwide. "It has to function mechanically like a door, but it also has to function like any other element of the RF shield."
This means cleaning and lubricating it, to ensure it continues opening smoothly and easily. If the door has a compressor, that also needs to be inspected regularly. Turner recommends that providers additionally keep the RF seals of the door clean by scrubbing them down with a brillo pad or sanding sponge once a month.
“You can replace the RF door and RF window if the primary shield itself is still attenuating properly,” said Maslowski. “You can determine if the shield is performing properly by doing the RF attenuation test.”
In fact, if the artifacts can be traced back to something isolated like the door, that can be a relatively positive thing. It means the problem is simple and doesn’t involve other concealed parts of the barrier.
The first step in constructing or repairing any RF shield is to give the shielding manufacturer any preliminary layouts and detailed drawings of the room and MR system. (Photo courtesy of NELCO Worldwide)
“Repair work can be very minimal, for example, changing out a few components and a door, or very extensive such as re-tightening all the bolted connections on a shield wall and ceiling, which requires all the drywall to be opened up,” said Edward Baraghis, general manager for shielding at SDI Canada. Ultimately, he agreed that an RF test will be the deciding factor to determine whether or not an existing shield can be repaired or needs to be replaced.
As with all things, just because an RF shield may be salvageable, that doesn’t necessarily mean it should be. At a certain point, the value proposition for comprehensive repairs will fall below what you’ll get from investing in a replacement.
“When you start talking about replacing doors and windows, adding magnetic steel shielding and the time spent trying to locate and repair deficiencies in the shielding, the cost between a new RF enclosure and renovating the existing RF enclosure can sometimes become very close,” said Matt Boesel, RF division manager of PDC Facilities. “A new RF enclosure will come with a warranty whereas a renovation typically doesn’t. Sometimes that makes the decision for a new RF enclosure the better choice.”