Magnetic resonance imaging (MRI) is key when it comes to diagnosing and treating complex injuries or diseases. For spinal injuries or degeneration or different types of cancer there is rarely any better way to diagnose. Problems that may lead to serious conditions can be diagnosed at early stages with the help of an MRI scanner. In addition, patients neither feel pain nor are they exposed to radiation like they are during the application of some other imaging techniques.
Still the technology produces its own specific risks that must not be underestimated. Electronic implants might be influenced by the electromagnetic environment created by an MRI device. This can be life-threatening if it leads to malfunctions of pacemakers, for example. Also, different types of metal used in artificial hips or life sustaining devices may interact with the magnet field in a way that can harm patients and even medical staff operating the MRI.
This leads to the necessity to systematically test medical implants for their compatibility with MRIs. The obligation of manufacturers to have their products validated is a necessary pre-condition for their market entry. It also helps developers gain insights into how well their products work in the MRI environment and what might be improved to ensure compatibility.
How the Law Views MRI Compatibility
Regulatory guidances in all major markets of the world require compatibility testing and reporting of implants in MRI environments. The FDA for example obligates companies to conduct a pre-market review for products that are new on the U.S. market or have been substantially modified. In May 2021, the FDA recently updated its guidance “Testing and Labelling of Medical Devices for Safety in the Magnetic Resonance (MR) Environment” (Docket Number FDA-2019-D-2837). European regulators also address MRI compatibility testing in the 2017 Medical Device Regulation (EU 2017/745) that defines the conditions under which medical products may enter EU markets.
To meet regulatory requirements, companies producing implantable devices need to document that they fulfil the consensus standards accepted within the industry. In addition to ISO/TS 10974 which directly addresses active medical implants, the ASTM F2052, F2213, F2182, F2119, F2503 provide the state of the art for safety testing of passive medical implants in an MRI environment. A combination of all those standards is applicable to active and nonactive implants in the eyes of the regulators, including FDA, and shall be applied for labelling and testing of medical devices. There is no difference in the current requirements between FDA and EU MDR regarding the MRI safety testing of medical devices in MRI environment, as all the mentioned standards are considered acceptable practice and state of the art.
Classifying MR Safety of Products
A standard that is recognized in the U.S. as well as in the EU is ASTM F2503. When it comes to classifying MR safety of medical implants, the standard defines three labelings:
- MR Safe: can be applied without testing to any implantable device that poses no known hazards in any MRI environment, including those that do not include any magnetic, conductive or metallic materials.
- MR Unsafe: is the default category initially applied to all active implantable medical devices before testing. It includes devices that include magnetic, conductive or metallic materials and have not been proven to be safe under any condition, as well as those known to pose hazards in MRI environments.
- MR Conditional: is applied to devices that include magnetic, conductive or metallic materials and have been tested and verified to pose no known hazards in a specified MRI environment, and which are accompanied by labeling that specifies the conditions of use.
At a minimum, non-active (passive) implantable medical devices categorized as “MR Conditional” under ASTM F2503 have been tested for magnetically induced displacement force (ASTM 2052), magnetically induced displacement torque (ASTM F2213), image artifact (ASTM F2119), and radio frequency induced heating (ASTM F2182). Additional testing may be required, depending on the unique characteristics of the implantable device.