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Non magnetic materials perform an important part in MRI operation and safety. Whenever magnetic components are brought close to MRI machines, they pose serious safety risks.
Therefore in this blogpost we will tell you about right materials for MRI components as well as best machining techniques so you can machine them correctly.
Understanding MRI Compatibility
MRI machines usually produce very powerful magnetic fields. This field is up to 21,000 times stronger than Earth’s magnetic field. Therefore the use of non-magnetic materials becomes important to avoid accidents and assure safety in this highly-magnetic environment.
Magnetic components in MRI environments pose great risks. They attract ferromagnetic objects because of their strong magnetic fields and then turn them into projectiles. These projectiles can cause severe injuries and damage to equipment. Apart from that magnetic materials also affect imaging accuracy which in turn leads to unusable or inaccurate test results.
Materials Used in Non-Magnetic MRI Components
Aluminum
Aluminum, a paramagnetic material, is important to avoid magnetic field interference in MRI systems. It dissipates heat proficiently because of its outstanding thermal conductivity and improves machine performance.
Although less strong than titanium, aluminum is normally used for MRI compatible parts like shielding parts, heat dissipation systems and magnetic housings.
Brass & Bronze
Both brass and bronze show non ferromagnetic characteristics that are important for MRI environments.
Brass provides good machinability & electrical conductivity for switches and MRI connectors and has melting point of almost 900°C. Meanwhile bronze, which has melting point of 950 °C, is mostly used in high wear applications because of its low metal to metal friction coefficient.
Titanium
Titanium is non magnetic material that has outstanding corrosion resistance and biocompatibility. It does not interfere with the magnetic field of MRI and guarantees accurate imaging.
Titanium is broadly used in surgical tools, MRI compatible implants & machine parts.
Austenitic Stainless Steels
Some grades of austenitic steel (204,316,316L etc) have face centered cubic structure and are thus broadly used in MRI environments. These grades in addition to impressive corrosion resistance also provide biocompatibility which makes them suitable for scalpels and scissors. But improper processing or cold working can produce mild magnetic properties in these grades.
Machining Techniques for Non-Magnetic Materials
Electrical Discharge Machining (EDM)
In this machining procedure, controlled electrical discharges are used to shape non-magnetic conductive materials. This process, without making any mechanical contact, removes material in microscopic increments and obtains tolerance of ±0.005 mm.
The process makes complicated MRI components from austenitic stainless steel & titanium such as RF shield components and gradient coil supports.
CNC Machining
This is a machining process in which non magnetic materials are precisely shaped into MRI components through computerized control. This process removes material using multi axis cutting tool with tolerance of ±0.002 mm.
This technique is perfect for making complicated MRI parts using highly-precise milling, drilling and turning operations, for example connectors and MRI compatible housings.
Ultrasonic Machining
Ultrasonic machining removes material from brittle, hard and non-conductive substances (such as glass and ceramics) using abrasive slurry and high frequency vibrations. This non-thermal process guarantees no heat affected zones in order to protect integrity of material.
This process is useful for generating intricate & distinct shapes as well as microstructures in MRI-compatible components like precision tools & ceramics bearings.
Laser Machining
Laser machining is a non contact process in which laser beams are used to cut and engrave non-magnetic materials such as metals, polymers and ceramics precisely. This assures smooth edges and minimum material distortion along with outstanding accuracy.
This technique is suitable for MRI compatible components that require clean finishes and precision. For example micro tools and thin walled structures.
Additive Manufacturing
Additive manufacturing processes use materials such as stainless steel, titanium and PLA to construct non magnetic components layer by layer. This process uses CAD designs directly to create complex shapes. Apart from reducing material waste, this process also improves design adaptability and assures biocompatibility. Thus this technique is best suited for making gradient shields, custom testing phantoms, complicated RF coils etc.
Quality Assurance & Testing in MRI Component Manufacturing
Non-Destructive Testing (NDT)
Non destructive testing evaluates non magnetic components without compromising their integrity through radiographic, eddy current and ultrasonic testing.
Ultrasonic testing can detect sub surface defects at frequencies between 20 and 40 kHz; whereas radiographic testing helps inspect internal structures with resolution of 0.001 mm, using X-rays or gamma rays.
Dimensional Inspection
Dimensional inspection assures that non magnetic MRI components meet design specifications and tolerances. So several inspection machine are used for this purpose— such as coordinating measuring machines, optical scanners and X-ray imaging devices.
These devices verify internal and external dimensions without damaging parts. This inspection process guarantees that each component functions and fits correctly in MRI system.
Surface Roughness Measurement
Two primary metrology techniques used to measure surfaces of MRI components are laser interferometry & atomic force microscopy.
Atomic force microscopy provides nanoscale resolution down to 10μm for detailed surface analysis whereas interferometry measures large areas quickly with sub-angstrom accuracy. Both of these methods assure microscopic detail and overall surface quality verification of MRI compatible parts.
Magnetic Susceptibility Testing
MST uses digital “Gaussmeters” and “precision Gouy balances” to measure material’s response to applied magnetic field.
This protocol measures field deformation at field strength of more than 3T using MR imaging in specimen vicinity. Hence this verification step assures that components maintain desired non magnetic properties.
Applications of Non-Magnetic Machined Components in MRI Systems
MRI-Compatible Tools & Instruments
MRI compatible tools and instruments are designed for high magnetic fields so that they can function well without interference.
Such tools and instruments are maintenance toolkits, diagnostic devices, surgical instruments etc. These tools not only assure accurate imaging and maintenance but operational safety too in MRI environments of more than 7T.
Patient Handling Equipment
MRI environments require non-magnetic patient handling equipment such as stretchers & MRI compatible wheelchairs to assure better patient transport and safety. These devices meet strict MRI compatibility standards for safe operation during imaging procedures and prevent magnetic interference as well.
Electronic Components
Non magnetic electrical components are important to the reliable operation of MRI setups. These components include RF interconnects, capacitors, connectors etc. They assure transmission of electric signals without any interference from magnetic fields.
Mechanical Assemblies
MRI machines use non magnetic mechanical assemblies such as motors, fasteners and structural elements which are important for internal operations. These assemblies guarantee stable operation as well as maintain accurate alignment and provide vibration damping. Hence this in turn assures scanner integrity and supports patient positioning in environments with great magnetic field.
To Sum Up
In short both non magnetic materials and accurate machining techniques are important to MRI performance, image accuracy and safety. Therefore strict quality controls along with advanced manufacturing processes are needed to assure consistent production of MRI compatible components.
If you require any kind of CNC machining services for non magnetic MRI components, then RICHCONN is best option. You can contact us anytime.
Common Questions
How do manufacturers verify non-magnetic properties of machined components?
Manufacturers use Gauss meters and SQUID magnetometry to measure magnetic susceptibility. These tests verify that components meet required MRI compatibility criteria．
How does the machining process ensure the biocompatibility of MRI components?
CNC machining creates ultra-smooth surface finishes as well as applies non-toxic corrosion-resistant coatings and uses medical grade titanium to assure biocompatibility．
Are there any specific cooling or lubrication requirements during the machining of non magnetic materials?
Yes special lubricants and coolants are required during machining procedure. They maintain accuracy, prevent thermal damage and protect surface integrity throughout the machining process．
How does the machining of non-magnetic components differ from that of magnetic ones?
Non magnetic component machining requires special equipment & tools in order to avoid cross-contamination. Besides that, the process requires tight control over tool selection, cutting parameters and finishing operations to maintain non magnetic properties.
