Posted 26 June 2015
By Alexander Gaffney, RAC
For the second time in a year, the US Food and Drug Administration (FDA) has released new guidance intended to ensure the safety of implanted medical devices from magnetic resonance imaging (MRI) devices.
In medicine, the context of a product's use is very often the difference between a product that cures and one that kills. For example, a medicine given in the wrong dose or to the wrong patient might leave someone injured or dead.
But for medical devices, there's another concern: environmental factors. The right medical device in the right patient can be dangerous under certain environmental conditions.
The issue has received some prominent attention from FDA in recent months. In December 2014, it released a draft guidance, Establishing Safety and Compatibility of Passive Implants in the Magnetic Resonance (MR) Environment, which explained that MRI devices can displace devices, heat devices through radiofrequency, or obscure the intended imaging. The regulator said all passive implants must be labeled with specific information regarding their use within the magnetic resonance environment.
"Testing should encompass the range of sizes of the device you intend to market," FDA explains in the guidance, and testing should anticipate "the worst-case scenario for each test." Regulators said they are particularly interested in seeing data about magnetically induced torque, displacement force and heating of tissue around the device.
Findings should ultimately support a label of "MR Safe," MR Conditional" or "MR Unsafe," FDA said. An "MR Conditional" finding should be accompanied on the label of the device with the conditions under which it can be used safely in an MR environment.
For more on this issue, please read our Focus Feature article, "Magnetic Resonance Safety Testing and Labeling for Devices."
In addition, in March 2015, FDA announced it had teamed up with the MED Institute to research the effects of radio frequency on the heating of passive metallic medical devices during MRI procedures.
Now FDA is out with a second draft guidance, also aimed at the safety of passive medical devices in the magnetic resonance environment.
The draft guidance, Assessment of Radiofrequency-Induced Heating in the Magnetic Resonance (MR) Environment for Multi-Configuration Passive Medical Devices, aims to provide the medical device industry with "paradigm" with which to assess passive medical devices for susceptibility to radiofrequency (RF)-induced heating.
The difference between the first guidance and the second is the latter's focus on multi-configuration devices—products made using several components, or products available in a variety of sizes or shapes.
"For these multi-configuration passive devices, it is typically not possible to leverage RF-induced heating testing from one device configuration or combination to other device configurations or combinations because the geometry or configuration of the device can affect heating in a non-linear manner," FDA explains in the guidance. "As a result, the total number of possible configurations or combinations that need to be assessed for RF-induced heating of some passive devices can be very large."
FDA's guidance goes on to describe its recommended process for testing devices, including the scientific rationale behind testing devices, and the minimum number of configurations and combinations that must be tested as a condition of approval.
FDA said many tests will be able to be skipped using statistical sampling methods and sensitivity analyses.