The Use of Magnets in the Medical Field: A Practical Guide

Magnets are used throughout the medical field, from the large magnets inside MRI scanners to the much smaller components found in pumps, sensors and hearing devices. They can help create images, deliver magnetic stimulation, hold external components in place and control movement inside medical equipment.

Some of these applications are highly specialised, while others use magnets in much the same way as equipment in other industries. This guide looks at some of the main uses of magnets in medicine, as well as the factors that need to be considered when choosing a magnet for a medical application.

How Are Magnets Used in the Medical Field?

Magnets have a range of uses in medical equipment, treatments and healthcare settings.

Magnets in Magnetic Resonance Imaging (MRI)

An MRI scanner uses a strong magnetic field, radio waves and signal detection to produce detailed three-dimensional images without the ionising radiation used in CT scans.

Because the main magnetic field is always present, MRI scanners need strict safety controls. Magnetic objects can be attracted towards the scanner, and a consensus statement from the Canadian Heart Rhythm Society and the Canadian Association of Radiologists notes that the scanner can move, heat or interfere with some implanted heart devices.

MRI compatibility depends on the individual device. Implants are generally labelled MR Safe, MR Conditional or MR Unsafe. An MR Conditional device can only be scanned under the conditions specified by the manufacturer.

Magnets in Treatment and Therapy

Transcranial magnetic stimulation (TMS)

Transcranial magnetic stimulation (TMS) uses an electromagnetic coil positioned against the scalp to deliver magnetic pulses. These pulses induce small electrical currents in targeted areas of the brain.

Health Canada approved TMS in 2002 for depression that has not responded adequately to medication.

Magnetic nanoparticles

Magnetic materials are also being researched for applications such as cancer treatment, while magnetic iron oxide nanoparticles are being studied for targeted drug delivery and controlled heating of tumour tissue.

These applications require carefully designed particles and controlled magnetic fields.

A note on magnet therapy

Static magnets are also sold in products such as bracelets, insoles and mattress pads for pain relief. However, a systematic review published in the Canadian Medical Association Journal concluded that the evidence does not support the use of static magnets for pain relief.

Magnets in Surgery

Magnets can have some very specific roles in surgical procedures.

Specialist magnetic instruments can be used to remove magnetic metal fragments from inside the eye. In some heart rhythm procedures, a soft catheter containing small permanent magnets in its tip can be steered using external magnets.

These applications require magnets and magnetic systems to be designed around the particular procedure rather than simply selecting a standard magnet from a catalogue.

Magnets in Dentistry, Implants and Prosthetics

In dentistry and implantable devices, magnets can be used to hold, align or connect components while still allowing them to be removed or repositioned when needed.

• Dentistry: Magnetic attachments can be used to retain removable overdentures and some facial prostheses, while still allowing them to be removed for cleaning.
• Reflux implants: The LINX device is a flexible ring of titanium beads containing magnetic cores. It is placed around the lower oesophageal sphincter, the muscular valve between the oesophagus and stomach. Magnetic attraction helps keep the valve closed, while swallowing separates the beads so food can pass.
• Hearing implants: Cochlear implants and some bone conduction hearing systems use magnets to hold an external coil or sound processor against the scalp. Magnet strength is matched to the patient to help prevent skin damage.

Magnets Inside Medical Devices and Equipment

Magnets are found inside many types of medical equipment. Neodymium can be useful for these applications because it provides a strong magnetic field from a relatively small component.

• Sensors: A small magnet paired with a Hall-effect sensor or a reed switch can confirm a component's position. For example, it could indicate whether a pump door is closed. In this type of application, the important consideration is the magnetic field at the sensor, rather than the magnet grade alone.
• Miniature motors and pumps: In brushless DC motors, permanent magnets rotate with the rotor to help drive compact pumps, fans and other equipment.
• Magnetic couplings: Magnets can transfer rotation through a sealed wall, allowing a pump to move fluid without a shaft passing through the wall. This can remove the need for a conventional shaft seal that could potentially leak.
• Laboratory equipment: Magnets can separate magnetic beads from samples, hold covers in place and help drive stirring mechanisms in laboratory analysers.

The choice of magnet depends on the equipment, available space, required strength and operating conditions. If you're developing a medical device or equipment component and aren't sure whether a stock magnet will work, Jobmaster Magnets designs and builds custom magnetic solutions and can help you work through the requirements.

Everyday Magnets in Hospitals, Clinics and Home Care

Magnets are also used for simpler jobs in hospitals, clinics and care settings.

They can hold corridor doors open, organise instruments, secure whiteboards and signage, or act as catches on cabinets and other fittings. At home, magnetic closures on adaptive clothing can make dressing easier for people with limited dexterity.

For these applications, the holding force, size, environment and method of attachment all need to be considered when choosing a magnet.

Which Magnets Are Used in the Medical Field?

The material used depends on what the magnet needs to do. Common permanent magnet materials used in device components include:

While neodymium magnets are known for their exceptional magnetic strength, they are generally more sensitive to heat than other magnet types, such as ceramic. So a higher-strength magnet isn't necessarily the best choice for an application involving motors, heating elements or sterilisation cycles.

Jobmaster Magnets stocks neodymium magnets in a range of grades and sizes. If an application has specific temperature, space, corrosion or performance requirements, the team can also discuss whether a different material or custom assembly would be more suitable.  

What Makes a Magnet Suitable for Medical Use?

A "medical grade" label alone doesn’t establish suitability. The material, coating, housing and finished device all need to be considered in relation to how the component will be used.

Coatings and corrosion protection

Neodymium can corrode when the alloy is exposed to moisture, so coatings such as nickel or epoxy are commonly used for corrosion protection. Depending on the application, the magnet may also be enclosed within a stainless steel or polymer housing.

The coating or housing needs to suit the environment, particularly where the magnet could be exposed to moisture, cleaning chemicals or other substances.

Biocompatibility

For devices that come into contact with the body, biocompatibility is an important consideration. In Canada, medical devices are regulated by Health Canada, and Class II to IV devices must be licensed before they can be sold. Biocompatibility is generally evaluated for the finished device, including relevant processing and sterilisation considerations, using recognised standards such as ISO 10993-1, rather than for an individual component in isolation.

Temperature and sterilisation

Heat, steam and chemicals can affect magnets, coatings and adhesives. The magnet's grade and protective materials therefore need to be considered alongside the highest temperature the component will experience and the cleaning or sterilisation process involved.

For an application with demanding temperature or cleaning requirements, discuss those conditions when selecting a magnet rather than choosing based on magnetic strength alone.

Tolerances and documentation

In a small assembly, even the thickness of a coating can affect the available air gap and therefore the performance of the finished component.

Depending on the project, buyers may also require documentation such as RoHS or REACH material declarations, certificates of conformance or lot traceability. These requirements should be discussed when requesting a quote so the right materials and documentation can be considered from the start.

Frequently Asked Questions

Why are neodymium magnets used in medical devices?

Neodymium magnets can provide a strong magnetic field from a relatively small, lightweight component. This can be useful when designers need to keep sensors, motors or retention systems compact.

Magnetic strength is only one part of the selection process, though. The grade needs to suit the operating temperature, while the coating and any housing need to suit the environment and intended use.

What type of magnet is used in an MRI machine?

Most hospital MRI scanners use superconducting electromagnets. These use cooled coils carrying large electric currents to produce the scanner's magnetic field.

Some open or low-field scanners use permanent magnets instead. These systems are very different from the small permanent magnets found in individual medical devices because an MRI scanner needs a large, stable and highly uniform magnetic field.

Can magnets affect pacemakers or other implants?

Yes. Strong magnetic fields can affect the operation of some implanted medical devices.

In a 2022 public advisory about sleep therapy masks with magnetic clips, Health Canada listed implants that magnets can affect, including pacemakers, defibrillators, neurostimulators, cochlear implants and magnetic denture attachments. For other implants that could be affected, it advised keeping the magnets at least 15 cm (6 in) away. That advice related to specific products rather than every type of magnet or magnetic application.

If you have an implanted device, follow the guidance provided by the device manufacturer and your healthcare professional. 

Sourcing Magnets for Medical Applications

For medical applications, magnetic strength is only one part of the specification. Material, grade, size, coating, housing and operating conditions can all affect whether a magnet is suitable for the finished application.

If you're developing medical equipment or a magnetic component, tell Jobmaster Magnets Canada what the magnet needs to do, the available space, operating and cleaning conditions, quantity and any documentation requirements. 

Contact the Jobmaster team to discuss whether a stock component could work for your application or whether a custom magnetic assembly would be a better fit.