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MRI Radio Frequency Shielding SITE PLANNING GUIDE

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MRI Radio Frequency Shielding SITE PLANNING GUIDE MRI Radio Frequency Shielding SITE PLANNING GUIDE Table of Contents Introduction ...................................................................................... 4 - 8 Chapter One - MRI Basics ............................................................... 9 - 14 Chapter Two - Radio Frequency Shielding ................................ 15 - 20 Chapter Three - Magnetic Shielding ........................................... 21 - 24 Chapter Four - Siting Considerations ......................................... 25 - 28 Chapter Five - Shielding Details Overview ................................ 29 - 31 - IMPERVIUS™ MRI Copper Panel System ............ 32 - 40 - IMPERVIUS™ MRI Galvanized Panel System ..... 41 - 49 - IMPERVIUS™ MRI Soldered Copper System ..... 50 - 58 INTRODUCTION WORLDWIDE.COM Who should review this guide? NELCO Facility managers, electrical and mechanical contractors, as well as architects and designers. Information provided within the NELCO Magnetic Resonance Imaging (MRI) is a Worldwide Site Planning Guide is an aid diagnostic imaging tool much like X-ray, to increasing your general knowledge and except it uses RF frequency and magnetic Phone: 781.933.1940 for planning your MRI facility. This is not a field instead of radiation. An MRI system substitute for the site planning information therefore needs to isolate the exam room of the MRI vendor whose equipment you from outside RF noise (local TV stations, are purchasing. Not every aspect of RF or cell phones, etc.) so it detects only the Magnetic shielding can be addressed in patient’s response to the RF frequency this brief guide, however we have tried to being broadcast. RF (Radio Frequency) give you a well-rounded view of the most shielding is required for EVERY common issues/concerns. MRI system. RF shielding can be done with nearly Questions and comments relating to any type of metal, however the most this guide can be directed to: commonly used metals are copper, galvanized steel or aluminum. It should be Global Director for RF Shielding noted that RF shielding NELCO Worldwide MUST surround the Magnetic field is mainly a MRI room, i.e., all walls, concern when looking at the 781.537.3011 ceiling and floor. RF MRI-generated field versus signals can transmit what it may impact around through concrete and earth, albeit to a lesser the MRI exam room. degree than open air but still enough to interfere with the MRI’s ability to get a clean image of the patient. 4 WORLDWIDE.COM NELCO This differs from X-ray shielding, where you Another concern of the magnetic only need to shield for the line of path of the field is that which is generated by Phone: 781.933.1940 radiation, sometimes called “line of sight.” moving cars, trucks, buses, An MRI also uses a strong magnetic field, electrical substations or other along with the RF frequencies, to create significant power line/equipment. the image of the patient. image of the patient. Magnetic shielding The 5-gauss field, a simple measure of may or may not be sufficient to guard the magnetic field, is the global guide to against these disturbances. Often MRI protect those people with pacemakers or vendors will consult the hospital/clinic to metal implants from the MRI-generated place the MRI far enough away so these magnetic field. Thus, if the 5-gauss field disturbances do not affect the MRI. When will extend into a hallway, waiting area or this is not possible, magnetic shielding other “uncontrolled” space where people will need to be considered. The shielding may go, magnetic shielding must be used solution can vary from site to site because to protect those people from exposure to of the uniqueness of each site, so the the 5-gauss field. hospital/clinic should employ an MRI vendor or other MR/RF/Magnetic expert These things create a type of magnetic to ensure that they plan properly early field that can interfere with the MRI, i.e., on to avoid problems later in the overall making the MRI unable to produce a clean planning/construction/installation cycle. 5 WORLDWIDE.COM NELCO It should be noted that most MRIs create a the MRI machine. This third layer of glass great deal of noise as they run through the can easily be added by the interior imaging sequences. finishes contractor. Phone: 781.933.1940 As such, consideration should be given to Most MRI systems today use liquid helium planning good sound-deadening elements to operate. into the MRI room construction. This requires a pipe, called a “quench Most of the sound deadening will come pipe,” to be attached to the MRI and through proper design and construction vented to the outside of the building. of the walls, ceiling and floor of the space. The RF shield can provide some sound The concern here is that liquid helium is attenuation as well, however the most very cold, and if, for some reason, there important elements of the RF shield, from was an accident (usually called a “quench” a sound attenuation perspective, are where the pipe breaks or leaks due to the the RF door and window. The RF door extreme cold or pressure), people could must be designed to provide good sound be harmed by the quickly expanding gas. attenuation; typically a rating of STC 40 or All MRI vendors provide guidance to the higher is recommended. The RF window mechanical contractor on how to construct usually comes with two layers of glass. and attach the quench pipe properly The process of adding a third layer of glass and safely. is usually sufficient to buffer the noise from 6 WORLDWIDE.COM NELCO Last, because most MRI systems generate into the MRI room, whether intentionally a very strong magnetic field in order to or accidentally, is slowly becoming a create the images of the patient, MRI mandate. As of the writing of this guide, Phone: 781.933.1940 safety is coming to the forefront in site it is not currently a requirement but is in planning more and more! discussion by several agencies to make it a requirement. Magnetic objects, if brought close enough to the MRI, could be quickly and strongly pulled into the MRI. The force and speed at which this can happen is “deadly”! Ensuring that some system/methodology is in place to be certain ferrous materials are never brought 7 8 Phone: 781.933.1940 NELCOWORLDWIDE.COM CHAPTERONE MRI Basics MRI BASICS WORLDWIDE.COM NELCO 1.1 Image of the Patient In layman’s terms, the human body consists of billions of molecules, all with Phone: 781.933.1940 their own magnetic dipole, each randomly oriented within the body. An MRI creates an image of the patient by placing the Molecule orientation in magnetic field patient in a very strong magnetic field, which will align the many billions of molecules in a north-south position [Image 1] within the MRI. A specific RF signal is generated by the MRI scanner to N S elicit a reaction from specific molecules N N S S of the patient. As an example, a “specific RF signal” may The entire body is made of molecules with a magnetic dipole be an RF pulse at 30.497 MHz, which may be the resonance frequency of a Z Z Z Z Z Z certain molecule. Thus, those molecules RF RF RF will “resonate” or oscillate Z Z Z [Image 2] Y Y Y Y Y Y and generate a response RF signal RF RF [Image 3]. As the MRI scanner runs XYX X XY X XY through a series of “specific” RF signals and collects responding signals from the X X X patient’s body, it can formulate an image [Image 1] [Image 2] [Image 3] from this information. Molecule at rest Resonating from RF reply signal- effect RF signal of resonating CHAPTER 1 • 10 A higher field MRI system should function faster. WORLDWIDE.COM NELCO 1.2 Benefits of a Stronger MRI System Phone: 781.933.1940 Generally speaking, the benefit of having a stronger MRI system is a stronger signal- to-noise ratio, which merely means the image quality should be better, all things being equal. Additionally, a stronger MRI system should function faster and thus allow for higher patient throughput. Image quality Lower field MRI, i.e., 1.5T Higher field MRI, i.e., 3.0T – generally faster scan time Patient throughput comparison Higher patient throughput and better image CHAPTER 1 • 11 WORLDWIDE.COM NELCO 1.3 MRI or X-rays 1.4 How MRI Works Phone: 781.933.1940 MRI is ideal for imaging soft tissue such When planning an MRI system, one should as heart, lungs, liver, etc. because soft take care not to place it near large metal tissue resonates more readily and has a objects, i.e., not to place an MRI directly much more pronounced reaction than hard above a structural beam. The metal beam tissue. X-rays, in contrast, are ideal for being so close to the MRI will prevent the hard tissue such as bones. MRI from establishing a “homogeneous” area where the patient is to be scanned. X-ray uses a small amount of radiation Thus, when magnetic shielding is to be that passes through the body to quickly used, the magnetic shield designer should capture a single image of your body. take care to ensure that no significant Bone blocks the radiation and thus amount of steel is too close to the MRI forms the image. such that it cannot compensate for the steel. This is called “shimming.” MRI combines a strong magnetic field with radio waves to get images by capturing The strength of an MRI is measured in molecule reaction to the radio waves. TESLA. A 3.0 Tesla (30,000 gauss) MRI system is approximately twice as strong as MRI requires RF shielding, whereas X-rays a 1.5 Tesla (15,000 gauss) MRI system.
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