For all the interesting gadgetry involved in MR imaging, it’s easy to forget there is a vital element hiding behind the scenes that makes it all possible – the radiofrequency shield.

In fact, it’s not unusual for this essential component to receive little or no attention on a day-to-day basis from the end users who operate from within it.

Neglecting a shield increases the likelihood of radiofrequency waves leaking into the room, distorting images and adding delays to potentially urgent patient diagnoses and treatment.

And it isn’t only individual patients who suffer from a compromised MR shield. Providers can expect hefty fees to repair shields, or in some cases, be faced with purchasing a completely new one if the damage is too extensive.

So what does it take to prevent radiofrequency waves from sneaking in and holding your facility hostage?

Although no shield lasts forever, getting smart about installing and maintaining your shield can increase its longevity and ensure deterioration is detected early – before it becomes a bigger problem.

Selecting the right materials
When choosing a shield, different metals will offer different strengths, a major factor in the life expectancy of a shield. The three most common materials used to construct shields are copper, aluminum and galvanized steel.

“There is little argument that copper is superior because of its conductivity factors and long-term reliability … the other two types of material, aluminum and steel would have less of a warranty from a shield integrity perspective,” Mike Krachon, director at IMEDCO, told HealthCare Business News. “That is why just about every supplier would recommend copper if it can be afforded. It is the most expensive solution but it is also often the preferred approach.”

Shield manufacturers recommend copper as it is more conductible than aluminum and galvanized steel, possessing a greater ability to resist the flow of radiofrequency waves. It also can withstand elements, such as water, more efficiently and is warranted with life expectancy rates starting at 10 years or more whereas galvanized steel expectancy rates are typically around five years. Welded aluminum can last for around ten years but the majority of vendors use paneled aluminum which has a life expectancy rate typically of three to five years.

Still, these alternative materials sometimes offer more than just a budget-friendly price tag. For example, aluminum is recommended as a better option for resisting certain types of interference.

Where and how to install an RF shield
From location to design, many factors can make or break a shield in the first few years of use, even before installation takes place, and should be considered very carefully.

For example, installing a shield on the outside wall or ceiling with windows will leave it more exposed and susceptible to the elements, increasing the risk of water damage.

“Whether it be copper or aluminum or even mesh for that matter, temperature differences on the inside versus outside, buildings with hydrostatic pressure, or unwanted building equipment-plumbing leaks are all concerns for moisture that can lead to oxidation and depending on what kind of shield material your shield is made of, the oxidation will begin degrading your shield system more rapidly,” says David Geiger, vice president of Americas sales at ETS-Lindgren.

He suggests that if a shield must be on the outer wall, supervision of the temperature is a must. “You want to look to treat that air between the shield system and the parent building or somehow maintain the temperature in that space between the space and the shield.”

Exhaust pipes, which can accumulate condensation from cold weather, can also create problems in this location with water dripping down to the shield. Pipe breaks and roof leaks also pose high risks here.

Checking the site and condition of the shield is the best way to combat this issue, but location alone is not enough to protect shields from water damage. The design of the shield is also essential.

For instance, a monolithic or bonded floor system is better for MR rooms because they protect more against moisture compared to MDF boards or floors that consist of wood in the composition and will absorb more water.

The designs of the room and shield are becoming more complex and can present even greater challenges with the involvement of building codes with providers constantly required to stay updated on new regulations when building or renovating property, such as the recent addition of rules governing seismic activity.

“That’s affecting the shielding industry more so than it ever has before,” says Krachon.

The design concept as to how the shield is assembled and installed can also affect RF shield effectiveness and reliability. Long term issues can arise based on how the seams of the panels or sheets are joined and how outside environmental issues such as shield vibration, moisture and humidity, and the structural stability of mounting frames and fastening methods impact these seams and joints. Sites with irregular shield floor plans and site space constraints put even more emphasis on design durability.

Ken Wilkens, a senior R&D engineer at the Vanderbilt University Institute of Imaging Science, is involved in the renovation of MR rooms at the institute and says it doesn’t hurt to add a few extra features.

“Another item, especially in the research environment, is to add extra blank penetration panels that can be filled out later,” he told HCB News. “It is much easier to add a panel when the room is being built then to add one later. If any functional imaging is planned, and space permitting, add a large waveguide along the magnet bore center behind the magnet. This will allow for a conventional projector, with appropriate lens, to be used instead of a specialty MR compatible projector. While the shield is being installed, there will be no scanning at all. In fact, the magnet will probably be ramped down during the process.”

In some cases, a shield might cost in excess of $200,000, but price can be a tell-tale marker in distinguishing a shield that will last three years from one that is still effective after ten.

According to Peter Haines, a project specialist for Banner Health, a non-profit health system, the price for each shield installation must be taken into consideration with the costs of other necessary items, such as LED lights and metal detectors.

Typically, he says, they can range from $65,000 to $100,000.

The price, conditions, design and location of a shield all should be considered before installations start and they are merely the first of many factors that determine how long a shield will last.

You have a shield … now what?

For some providers, the first shielding mistake is completing a successful installation and then believing they no longer have to think about it anymore.

“The majority of owners, hospitals and clinicians really seem to pay little attention to the shield maintenance packages,” said Krachon. “It’s not uncommon for users to be excited once a shield is installed and then not touch the thing again for their entire lifetime until they begin to experience imaging problems. They all have maintenance arrangements for the MRI but few have one for the shield which could have the greatest single impact on MRI performance."

One area that often is ignored is the door frame on which dirt and other materials build up over time and can interfere with the shield’s ability to block out radiofrequency waves.

“All HVAC in and out of the room will be a honeycomb mesh,” says Wilkens. “Over time the return will start to collect dust on the mesh and too much will start affecting the HVAC. These are easy to clean with a shop vacuum outside the room and long hose. You do not want to wipe with a rag as they can be bent fairly easy.”
Another overlooked element of shield maintenance involves the installation of new equipment, such as LED lights, which may require particular design and set-up to ensure they will not damage the efficacy of the shield.

Even more complex is breaching the wall where the shield lies to install wires and probes of different devices. This goes for equipment both in and outside the MR room as well as security technology and ferromagnetic detectors.

It is advised that providers seek out experienced contractors and set up communication between them and the shield vendors for extra support and to ensure proper installation.

Shield Edict
The best way to preserve the life of a shield involves prepping for installation, overseeing the installation and setting up a routine check a minimum of once a year following the installation. This includes checking doors for dirt or material buildup, conducting RF interference tests when new magnets are installed and determining the type of care a shield needs based on its location and design. In addition, look to a RF vendor with long term proven solutions and financial strength in case you do run into issues.

Some of these problems can be reduced or simplified, using specific equipment or certain tactics.

"Selecting a door with basic features can provide longer term performance and machined construction,” says Geiger. “High acoustic ratings are the most popular selections. Features with auto retracting latches or automatic opening controls are common issues in any style door that require routine maintenance and upkeep.”

Working with experienced manufacturers is another way to ensure minimal shielding headaches. Doing so will limit mistakes and may cost less if the provider has worked with the vendor before and has a good relationship.

“We have a vendor that has already installed over seven rooms at our location, so knowing the vendor well and how reliable they are is important to us, especially when doing upgrades that are on a very tight schedule,” says Wilkens.

These are just a few of the many ways to ensure that a shield will live out its full-life expectancy.