Precision in the Magnetic Field – myonic Ball Bearings for MRI-Guided Procedures

MRI-guided procedures are opening up possibilities today that would have been unimaginable just a few years ago. Physicians can perform interventions directly inside the magnetic resonance imaging (MRI) scanner while monitoring the position and movement of the instruments in real time.

To ensure safe operation, all instruments used in the MRI environment must be strictly non-magnetic. Even components containing the smallest ferromagnetic elements can heat up, significantly impair image quality, complicate the procedure, or, in extreme cases, become dangerous projectiles within the scanner room.

This is particularly challenging for components that often go unnoticed in clinical practice but play a crucial technical role: ball bearings. They enable precise, low-friction motion in catheters, guidance systems, rotating instruments, and robotic assistance devices, while remaining effectively “invisible” within the MRI environment.

How Is MR Safety Assessed?

The FDA (U.S. Food and Drug Administration), one of the world’s most influential regulatory authorities for medical devices, pharmaceuticals, and food safety, relies on internationally recognized testing procedures (ASTM standards) when evaluating MR compatibility.

At its core, the assessment focuses on two key questions:

1. Is the component attracted by the magnetic field?
2. Does it tend to align itself or experience torque within the magnetic field?

The following illustrations provide a simplified overview of how these tests are performed.

1. Determination of the Deflection Angle (ASTM F2052)

A component is suspended from a thin string or fixture and positioned at the location of the highest magnetic field gradient within the MRI scanner. If magnetic forces act on the component, it will be deflected from its vertical position. The resulting deflection angle is a direct measure of magnetic attraction:

• Small deflection angle → low magnetic attraction
• Large deflection angle → strong magnetic attraction

As a practical rule of thumb:

If the deflection angle is less than 45°, the magnetic force acting on the component is lower than the force of gravity and is generally considered acceptable. High-quality, non-magnetic components typically exhibit significantly lower values (e.g., 0° to 20°) and remain virtually unaffected by the magnetic field.

2. Determination of Magnetically Induced Torque (ASTM F2213)

The component is mounted so that it can rotate freely.

It is then placed within the magnetic field:

• If the component remains stable, the induced torque is very low and the component is generally considered suitable for use in the MRI environment.
• If the component tends to rotate noticeably or snaps into a preferred orientation, this indicates the presence of ferromagnetic materials. In such cases, its use in MRI applications may be severely restricted.

For safe MRI use, it is essential that no uncontrolled self-rotation or alignment within the magnetic field is observed.

3. Additional Requirements

In addition, manufacturers must demonstrate that their components do not cause any safety-relevant heating (ASTM F2182) and do not adversely affect image quality beyond acceptable limits (ASTM F2119).

While these tests are an important part of the overall MR safety assessment, they typically follow the fundamental question of whether a component remains mechanically stable within the magnetic field and does not move unintentionally.

The combination of these test methods enables the FDA to reliably assess whether a product can be used safely in the MRI environment.

4. Non-Magnetic Bearings from myonic

myonic develops ball bearings specifically designed to meet these demanding requirements. A specialized nickel-based alloy combined with a precisely controlled heat treatment ensures that the bearings:

• exhibit virtually no deflection and no measurable torque in magnetic fields
• provide mechanical properties very similar to those of conventional steel ball bearings
• offer excellent corrosion resistance at the same time

As a result, myonic bearings enable smooth, low-friction, and low-vibration operation even under the unique conditions of the MRI environment. They make a significant contribution to the accuracy and reliability of MRI-guided procedures and support the continued advancement of modern minimally invasive treatment concepts.

For more information on the materials, testing methods, and application areas of our non-magnetic bearings, please contact us or speak with one of our experts.