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Premier Security Ballistic & Blast Ltd
MRI Shielded Rooms and RF Faraday Cages
Premier Security Ballistic & Blast Ltd provides radio frequency shielding for MRI examination rooms in the form of a copper clad Faraday cage, together with the shielded doors, viewing windows, service filtering and helium quench pipe systems that complete the installation.
An MRI scanner is, in effect, an extremely sensitive radio receiver. It detects signals measured in microvolts, and the ambient radio frequency environment of any modern building is many orders of magnitude noisier than that. Without a shield, external RF energy reaches the receiver coils and appears in the reconstructed image as artefacts, banding or wholesale loss of diagnostic quality.
The shield is therefore not an optional refinement to the room. It is a functional prerequisite for the scanner to produce usable images at all, which is why scanner manufacturers publish shielding requirements as part of their site preparation specification and will not sign off an installation without them being met.
Why an MRI Scanner Needs a Faraday Cage
Magnetic resonance imaging works by exciting hydrogen nuclei with a radio frequency pulse and then listening for the faint signal they emit as they relax. The frequency of interest is determined by the field strength of the magnet, which places a 1.5T system in the region of 64 MHz and a 3T system in the region of 128 MHz.
Both of those sit squarely inside the range occupied by broadcast transmissions, mobile communications, building services equipment and ordinary electrical noise. Any of it reaching the receiver will compete with the signal the scanner is trying to detect.
A Faraday cage resolves this by enclosing the examination room in a continuous conductive envelope. Radio frequency energy striking the envelope is reflected and dissipated rather than passing through, and the scanner operates inside an artificially quiet electromagnetic environment.
An MRI shield fails at its apertures, not its panels. The door, the window, the ventilation and every cable entering the room are where diagnostic image quality is won or lost.
MRI RF Shielded Room Construction
We construct MRI RF shielded rooms as a copper clad panel Faraday cage, built to meet the requirements of the major scanner manufacturers including Siemens Healthineers, Philips, GE HealthCare and Canon Medical.
Acoustic insulation is incorporated within the construction, which matters more in MRI than in most shielded applications because gradient coil switching generates substantial noise during acquisition. Electrical power and data cabling is installed and every service crossing the shield boundary is filtered, so that conductors do not carry interference through an otherwise sound envelope.
The completed installation includes RF shielded doors, an RF shielded viewing window, waveguide ventilation and the penetration assemblies required for pipework and fibre optic entries.
RF Shielded Doors
The door is the largest moving aperture in the cage and the component whose performance most depends on daily use. It has to reseat correctly every time it closes, remain serviceable through very high cycle counts in a busy imaging department, and be operable by staff moving patients on trolleys and in wheelchairs. We provide shielded doors designed around ease of use and maintenance as much as around attenuation figures.
RF Shielded Windows
Visibility between the control room and the examination room matters both clinically and for patient reassurance, particularly for anxious or claustrophobic patients. The MRI window has to deliver the same level of shielding as the rest of the cage while remaining genuinely usable.
Our RF window uses two layers of blackened mesh to achieve the required RF performance. The layers must be positioned at a precise angle relative to one another, otherwise the overlapping mesh produces the visual distortion known as Fresnel interference and the window becomes difficult to see through. Windows are available in a range of sizes and frame designs, with or without mullions, with full installation and testing.
Waveguide Vents
Waveguide vents are a critical component of any shielded room, allowing air to pass while attenuating radiated interference. In an MRI suite they carry the additional burden of supporting the environmental conditions the scanner and the patient both require, so vent sizing has to be coordinated between the mechanical services design and the shielding specification early rather than resolved on site.
Helium Quench Pipe Systems
The superconducting magnet in an MRI scanner is cooled by liquid helium. A quench is the event in which the magnet loses superconductivity and that helium boils off rapidly, expanding to many hundreds of times its liquid volume in a very short period.
The quench pipe exists to route that volume safely to atmosphere outside the building. If it fails, or if it is undersized or incorrectly routed, the consequences inside the examination room are severe: oxygen displacement, a rapid pressure rise and a door that may become impossible to open against it.
We have extensive experience in the design and installation of MRI helium quench pipe systems, coordinated with the shield so that the penetration through the cage maintains electrical continuity without compromising the pipe route.
700x Liquid helium expands by roughly this factor as it boils to gas, which is why quench pipe design is a life safety matter rather than a services detail.
Pre-Construction Surveys
Two site conditions can render an MRI installation unusable regardless of how well the shield performs, and both are cheaper to establish before construction than to discover after commissioning.
- Vibration surveys. Mechanical vibration transmitted through the structure degrades image quality. Common sources include nearby plant, lifts, road and rail traffic and, in hospital settings, adjacent departments.
- Magnetic field fluctuation surveys. Moving ferrous masses such as vehicles, lifts and trolleys produce time varying magnetic field disturbance. Scanner manufacturers publish limits for this, and exceeding them affects image stability.
We can undertake both as a precursor to building the room, confirming that ground and site conditions fall within the scanner manufacturer's specified limits. Where they do not, remedial options are far broader at survey stage than they are once the slab is poured.
RF Shielding and Magnetic Shielding Are Not the Same Thing
This distinction causes recurring confusion at design stage and is worth stating plainly.
| Requirement | What it addresses | Method |
|---|---|---|
| RF shielding | Radio frequency interference reaching the scanner receiver and degrading images | Copper clad Faraday cage with filtered services and treated apertures |
| Magnetic shielding | The static magnetic field extending beyond the examination room into adjacent areas | Ferromagnetic material applied to specific walls, floor or ceiling as required by the fringe field plot |
A Faraday cage does not contain the static magnetic field, and ferromagnetic magnetic shielding does not attenuate radio frequency. Most installations need only the RF cage because the fringe field is managed through room layout and controlled access, but where site constraints put the five gauss line beyond the walls of the examination room, magnetic shielding is a separate design exercise driven by the manufacturer's fringe field plot.
Testing and Handover
Shielding effectiveness is verified by measurement on completion, against the attenuation levels and frequency range set out in the scanner manufacturer's site requirements. Testing should be a witnessed acceptance activity written into the specification, not a self certification exercise, because it is the point at which the room is confirmed fit for the equipment about to be installed in it.
We work with scanner manufacturers and main contractors throughout, which matters on MRI projects more than most: the shield contractor, the M&E contractor and the equipment supplier all have to hand over to one another in a fixed sequence, and slippage in one directly delays the others.
MRI Shielding FAQs
Why does an MRI room need to be shielded?
An MRI scanner detects extremely weak radio frequency signals from the patient, at frequencies around 64 MHz for a 1.5T system and 128 MHz for a 3T system. Ambient radio frequency energy from broadcasting, mobile communications and building equipment occupies the same range and will appear in the images as artefacts or noise. The Faraday cage creates an electromagnetically quiet environment so the scanner can detect the signal it is looking for.
Can an MRI shielded room be installed in an existing building?
Yes, and most are. Modular construction is well suited to retrofit within an existing structure. The determining factors are structural loading, available floor to soffit height, the route available for the quench pipe to reach atmosphere, and access for delivering both the panels and the magnet itself. Vibration and magnetic field fluctuation surveys are particularly important in retrofit situations.
Does the shielded room work with any manufacturer's scanner?
The cage is built to meet the site preparation requirements published by the scanner manufacturer, and we construct rooms covering the requirements of the major suppliers including Siemens Healthineers, Philips, GE HealthCare and Canon Medical. The specific scanner model should be confirmed before design begins, as requirements differ between manufacturers and between field strengths.
What is Fresnel interference in an MRI window?
The RF window uses two layers of fine blackened mesh. When two regular meshes overlap at the wrong relative angle they produce a visible moire distortion, which makes the window unpleasant and difficult to see through. Setting the layers at a precise angle to one another eliminates the effect while retaining the shielding performance that two layers provide.
Who is responsible for the quench pipe?
Responsibility varies by contract, which is precisely why it should be established early. The pipe has to penetrate the RF shield, route to a safe discharge point outside the building and be sized to the magnet, which places it at the intersection of the shield contractor, the mechanical contractor and the equipment supplier. We design and install quench pipe systems and coordinate the shield penetration as part of that work.