Advanced Imaging

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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Toward Safer MRIs

The critical role of non-magnetic interconnects for advanced systems
MRI chart
MRIs create powerful magnetic fields that align the magnetization of hydrogen atoms within the body. Radio waves alter the alignment of this magnetization, which causes the hydrogen atoms to emit a weak radio signal that is amplified by the scanner and manipulated to generate information that is used to reconstruct an image of the body.
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By Arnie Feinberg, Hypertronics Corp.

The correlation between advancing Magnetic Resonance Imaging (MRI) technologies and the furthering of key medical diagnostics is clear. For example, interventional MRI produces images used to guide minimally invasive procedures; radiation therapy simulation locates tumors in preparation for targeted radiation therapy treatment; and diffusion MRI enables researchers to make brain maps of fiber directions and thereby examine connectivity within different regions of the brain.

However, as MRI systems continue to grow even more sophisticated in functionality—providing more detailed images in increasingly faster times—a widely discussed technological issue assumes critical importance: namely, the role and associated adverse effects of magnetic components that are designed into MRI equipment.

To understand the significance, let's first review how MRI systems work.

In essence, MRI systems produce images through the interaction of strong magnetic fields and radio frequency signals. At the core of each MRI system is a magnet. MRI magnet strengths are measured in Tesla (T) units, which represent the property of magnetic flux density. Today's MRI systems have Tesla ratings ranging from 1.5T to 3T, with some 7T and 11T systems used on a limited basis in research and development phases and in testing. Other experimental magnets have ratings as high as 30T.

MRI scanners are offered in both tunnel- and open-architecture models. They create powerful magnetic fields that align the magnetization of hydrogen atoms within the body. Radio waves are used to alter the alignment of this magnetization, which causes the hydrogen atoms to emit a weak radio signal. This signal is then amplified by the scanner and manipulated to generate information that is used to reconstruct an image of the body. The image is subsequently processed by software to yield a digital image of the scanned area—making it possible for doctors and technicians to diagnose the patient without having to perform surgery.

Given this process, any magnetic components incorporated within MRI equipment negatively affect image quality by distorting the magnetic flux created by an MRI system's magnet. Distorted images can lead to misdiagnosis, exacerbated patient medical problems, and possible malpractice suits for hospital staff.

It's important to realize that high levels of iron, nickel, and cobalt—common trace elements found in copper alloys—also render components unacceptable for use in MRI imaging areas, since these metallic elements likewise distort the magnetic flux. In fact, even the selection of plastics used in components is critical, since some plastics can distort the magnetic flux even though they aren't magnetic.

There are still other problems associated with magnetic components. Like any magnet, an MRI magnet has the ability to attract other items with magnetic characteristics. Magnetic components used in everyday objects (pens, watches, wheelchairs and furniture) can become harmful—even lethal—projectiles when used within the range of an operative MRI magnet. Patients with surgically implanted metal components run the risk of having the MRI magnet shift the position of those parts, possibly causing internal damage. In fact, some patients who work with their hands, such as auto technicians and machinists, may unknowingly have steel particles embedded in their skin and their eyes—particles that can potentially be forcibly removed by an MRI magnet, resulting in serious injury.

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