MRI SHIELDING
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MRI SHIELDING ARCHITECTURAL SITE PLANNING GUIDE Abbott Northwestern Hospital, Minneapolis, MN Sept. 2009- Rev. C 400 High Grove Boulevard • Glendale Heights, IL 60139 • (630) 307-7200 Phone • (630) 307-7571 Fax www.ets-lindgren.com • info@ets-lindgren.com

An ESCO Technologies Company Section 3 Before the Shielding Section 5 Magnetic Shielding Section 6 Siting Considerations/Requirements

Magnetic Resonance Imaging (MRI) is a diagnostic imaging tool that uses magnetic fields and radio waves to generate an image of the patient. It is different from X-ray in that it does not expose the patient to anything harmful and is a much better tool for soft tissue imaging, whereas X-ray is ideal for hard tissue such as bone. An MRI is primarily defined by its field strength. For clinical applications, low field magnets are generally less than 1.5 Tesla while 3.0 Tesla is considered high to very high. Research magnets often range from 0.2 Tesla to above 20 Tesla. MRI shielding is also...

Philips Open Magnet Clinical MRI systems are produced by companies such as General Electric Healthcare, Siemens Medical Solutions, Philips Medical Systems, Hitachi Medical Systems and Toshiba Medical Systems. Others produce specialized MRI systems such as ONI and Esaote. And, there are those that provide a unique system that utilizes the MRI produced by one of these companies, but augments it with special features or applications such as BrainLab or IMRIS. Some research MRI system manufacturers include Magnex Scientific/Varian Medical, Bruker, and Oxford Instruments. There are also MRI...

Ferromagnetic Detection System Often overlooked are the things you need to do before RF shielding is installed. Every site should be evaluated for electromagnetic interference (EMI) and vibration prior to finalization of the site. If your site has excessive EMI and/or vibration, you may not be able to fully utilize your MRI scanner once it has been installed. EMI is typically generated by nearby elevators, electrical distribution within the building, nearby car parking or roads and paths as well as electric trams, subways, etc. The level of EMI can be reduced with shielding; however, it is...

RF shielding is required for every clinical MRI system and most research systems. However, performance may vary based upon the particular MRI system. Always check with your MRI system manufacturer to confirm specific requirements. Following are general RF shielding sense frequencies: While most MRI manufacturers will require 100 dB of RF attenuation at the sense frequency, the requirements may vary for any given manufacturer and for higher-frequency testing specifications. RF shielding can be made of virtually any type of metal; however, the most prominent types used for MRI shielding are...

Section 4.1 RF Flooring There are three basic types of RF flooring: monolithic copper, modular cell type, and pan form. Monolithic copper requires a normal 1” depression/buildup, is moistureresistant, and has a cement-like underlayment as a finish. This is the recommended RF floor system for MRI applications. Monolithic Copper Flooring The modular cell type floor is a panel system requiring a depression/buildup of 1 1/8” to 1 3/8” with identical construction to that of the cell wall and ceiling panels. It is a wood core with laminated metal on both sides of the core. A vapor barrier is...

Section 4.2 RF Filters & Waveguides The RF shield forms a complete box around the MRI system. Everything that is to come into the MRI room must pass through an RF filter or waveguide. RF filters are mounted on the RF shield and create an penetration point for electrical power for lighting or powered outlets within the MRI room. RF filters also accommodate data cables. Waveguides are penetrations in the RF shield that allow a fluid flow into the MRI room. Air conditioning, water and medical gases all provide a fluid flow and require a waveguide. To confirm whether an RF filter or waveguide...

Magnetic Shielding Magnetic shielding is not required for every site and is often overlooked in the early planning stages. Essentially, the goal of magnetic shielding is to protect the environment from the MRI magnetic field. Magnetic shielding is not the same as lead shielding. Lead shielding is identified via “line of sight” whereas magnetic shielding must take into account the geometry of the magnetic field relative to the position of the magnetic shield. Magnetic shielding is usually fabricated with silicon steel in sheet form, but it can also be done in steel plate. Steel plate is not...

Siting Considerations / Requirements There are many facets to take into account when planning an MRI suite. The following are some key items to consider: If not, have it tested before finalizing the location. Testing can be done by either the MRI or shielding vendor. • Is the site suitable for the magnet from a vibration standpoint? • Is the site suitable for the magnet from an EMI noise standpoint? ________________________________________________________________ •What is the delivery path for the magnet? •Are the halls wide enough? Are they tall enough? •Is the floor strong enough? •Who...

• Have you considered the sound level of the MRI and will it impact surrounding offices or suites? Sound can be carried structurally through ducts or vents and even the penetration panel of the MRI system. Acoustic options for RF shielding consist of sound absorption material within RF panels, acoustic doors, and an additional layer of glass on RF windows. Consult your MRI vendor to obtain the acoustic levels of their equipment and then select a Sound Engineer who can evaluate your entire acoustic situation- not just RF shielding. ETS-Lindgren has partnered with a professional acoustic...

The Enclosure The preferred RF enclosure for MRI application consists of wood panels wrapped with copper. This provides a lightweight system that offers the best longevity in RF integrity. The panels are bolted together and to the floor system. The alternative consists of metal-wood-metal composite panels. Each panel is clamped to the adjacent panel to form the entire shield. It is heavier and introduces some amount of ferrous material around the MRI. Consult the MRI vendor for acceptance of this type of system. The Floor The RF floor should be moisture-resistant and consist of copper...