Plastic Alloy Enhances Image Clarity

September 2, 2002

3 Min Read
Plastic Alloy Enhances Image Clarity

Originally Published MPMN September 2002


Plastic Alloy Enhances Image Clarity

Material reduces interference in MRI applications

Zachary Turke

Thermoformed from the Kydex alloy supplied by Kleerdex Co., this phased-array neurovascular coil used with high-power MRI equipment does not cause interference.

For more than 10 years, Medrad Inc. (Pittsburgh) has produced fixtures and receiving coils for magnetic resonance imaging (MRI) equipment. Thermoformed from acrylonitrile butadiene styrene (ABS), these components record the energy emitted by hydrogen atoms in the body in the presence of a strong magnetic field. But when test data revealed that the ABS coils caused interference when used with newer, more-powerful MRI machines, the company realized it was time to find a new plastic material and turned to Kleerdex Co. (Aiken, SC).

"ABS was a fine material to use when MRI machines were long, narrow tunnels," explains Kleerdex marketing representative Richard Rapp. "But as designers have made these machines more open to allay patient anxiety, they have increased their magnetic power correspondingly to retain image clarity and accuracy. This causes problems for the plastic," he says. Like the human body, ABS contains loosely bound hydrogen molecules that are excited by the presence of the large magnetic fields produced by newer machines, resulting in the interference noted by Medrad. Kleerdex identified this shortcoming and suggested its Kydex alloy as an alternative material.

Made of acrylic and PVC, Kydex has more tightly bound hydrogen molecules than ABS. Medrad tried the alloy in some test coils and found that the material successfully reduced interference below detectable levels.

Clearer imaging is not the only benefit offered by Kydex. "MRI machines are typically placed in the center of high-traffic rooms, subjecting them to a lot of bumping, impacts, and repeated-use strain," says Rapp. The material helps to offset this wear and tear by offering an impact resistance of 18 lb∙ft, roughly double that of ABS. Certified as fire retardant to UL 94V-0 and V-5 standards, the material features a tensile elongation of 5800 psi, a modulus of elasticity of 347,000 psi, and a Rockwell hardness of 106. "Also, Kydex is cost competitive with flame-retardant ABS, and exhibits a broad chemical resistance. It also withstands repeated cleaning with strong cleansers without staining or fading," adds Rapp.

The Kydex alloy is compatible with a wide variety of manufacturing processes, including injection molding and vacuum, pressure, and thermoforming. Acceptable secondary processes for the material include sawing, filing, taping, gluing, and general machining. According to Rapp, Medrad was so pleased with these and other features of the material that they have made it the de facto standard for all their new parts. Rapp also sees applications for the material beyond MRI equipment. "Essentially, it's suitable for any medical instrumentation application where flame retardancy, high impact resistance, formability, and cleanability are important design criteria," he says.

Copyright ©2002 Medical Product Manufacturing News

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