MRI Shielding and RF Shield Enclosure Design Considerations

How to create a secure and functional MRI shield

MRIs are undoubtedly powerful machines (see the video below), but it's important to remember that they're also quite sensitive. In some cases, a slight external interference can have a huge impact on the MRI's ability to produce quality, diagnostically acceptable images.

For this reason, MRI imaging rooms need an effective radio-frequency (RF) shield for optimal MRI operation. RF shielding serves two important functions, including:

  • Preventing external electromagnetic radiation from distorting the diagnostic images
  • Preventing the MRI's own electromagnetic radiation from disrupting external medical devices

If you're building a medical imaging room, you'll need to plan for the room's MRI shielding and RF shield enclosure design. If you're furnishing an old room with a new MRI system, you should analyze the shield's effectiveness with the new technology.

For help with your RF shield enclosure, our experts have your back. We at PrizMED Imaging can either take an active role in building an effective shield or walking you through the process, depending on your preferences and budget.

 

The Importance of RF Shielding

As a quick Radiology 101 lesson, remember that MRI machines use radio-frequency (RF) to create images and so they have highly sensitive RF sensors. These sensors can pick up the radio-frequency electromagnetic radiation (RF noise) coming from outside of the MRI exam room. The potentially interfering RF noise comes from a wide variety of common electronic devices, such as transformers, motors, computers, and even cardiac monitors.

If the MRI exam room does not have an effective RF shield, then the incoming RF waves may affect the MRI's imaging.

 The ceiling, walls, doors, and windows in this image all work together to provide an effective shield.

To prevent this distortion, an RF shield enclosure features a "system" of interacting components, including:

  • Doors
  • Windows
  • Ceilings
  • Floors
  • Walls

Additionally, items penetrating the RF shield (power, HVAC, exhaust, piping, and plumbing) must pass through RF filters or waveguides.

All of these components work together to provide a functional shield barrier that reduces RF noise to acceptable levels.

 

Parts of an RF Shield Enclosure

All parts of the shielded system must feature the appropriate conductive materials, and when bonded together, these parts achieve a six-sided box (i.e., walls, ceiling, floor), also known as a "Faraday Cage."

In order to create a practical and cost-effective RF shield, some important considerations for the enclosure design should include:

  • RF Shield Walls/Partitions — RF shields often require three partitions, including the parent wall, the RF shield wall, and the interior finishing wall.
  • RF Flooring —  Floors in MRI exam rooms often require a structural subfloor, RF shielding, a protective layer, and other finish materials.
  • RF Door — Common types of RF door systems include single swing, double swing, sliding, double sliding, acoustic, non-acoustic, automatic, and manual.
  • RF Ceiling — An RF shield ceiling is often suspended from the structural deck overhead. Any services that must pass above the MRI scanner room (power, piping, cabling, and ductwork, for example) should do so in the plenum above the RF shield ceiling.
  • RF Windows — The window between the magnet room and control or console room usually requires RF shielding, which is often two layers of copper screens or perforated sheets.
  • RF Filters and Waveguides — Items that penetrate into the RF shield enclosure will require special fittings and materials to maintain shield integrity. RF filters and waveguides are common materials used at the shielding feed-through points.

 

Types of RF Shielding

A common RF shielding design incorporates solder seamed copper. Other popular types of RF shielding include galvanized steel and aluminum. Although RF shielding can include any type of metal, using metals other than the ones listed above can lead to various drawbacks, from corrosion to difficulties in handling.

Installing copper RF shielding in a planned MRI exam room

 

Other Considerations for the MRI Shielding

In addition to controlling RF noise, there are several other considerations you need to make for an optimal and safe MRI shield enclosure. For instance, you may need to include magnetic shielding to contain the magnetic field generated by the MRI, preventing it from interfering with surrounding areas. This type of shielding is not required for every site, but it is often overlooked when planning the shield enclosure design.

Think of magnetic shielding this way - have you ever tossed a metal object near an operating 3.0T MRI? First of all, this can be extremely dangerous. But in controlled tests, it's pretty cool to see the physics and the power of these machines.

Video Courtesy of practiCal fMRI

Seeing those metal objects slamming around the MRI's bore is a great reminder of the need for thorough safety measures, such as magnetic shielding, magnetic object detectors, and safety signage.

Furthermore, before installing the RF shielding, you also need to consider the site's electromagnetic interference (EMI) and vibration. If the planned MRI exam room has excessive EMI or vibration, you may not be able to fully utilize your MRI scanner after installation.

 

MRI Shielding and Enclosure Design With PrizMED Imaging

MRI shielding and RF shield enclosure design are two critical considerations of a well-functioning MRI system. With an FDA-certified MRI scanner from PrizMED Imaging, we can build or confirm your exam room shielding. Depending on your preferences and budget, we can either come to your site for an evaluation or walk you through the process via telephone and email.

To speak with a PrizMED Imaging technician regarding your MRI shielding and RF shield enclosure requirements, contact us online or call us today at 440-414-7539.

 

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