The new article describes the aspects related to safety considerations for medical devices used in MR environments. 

The Therapeutic Goods Administration (TGA), an Australian regulating authority in the sphere of healthcare products, has published a guidance document dedicated to clinical evidence for medical devices. The document describes the approach to be applied for clinical evidence used to substantiate the claims and statements made by medical device manufacturers when applying for marketing approval depending on the nature of medical devices and their specific features and characteristics. In particular, the document outlines the scope of clinical evidence required based on the type of medical device and risks associated thereto. It is also important to mention that the present TGA guidance is non-binding in its legal nature, and is not intended to introduce new rules or impose new obligations, but rather to provide additional clarifications regarding the applicable regulatory framework, as well as recommendations to be taken into consideration by medical device manufacturers and other parties involved to ensure compliance thereto. The authority also reserves the right to make changes to the guidance, should such changes be reasonably necessary to reflect corresponding amendments to the underlying regulations. 

The scope of the guidance covers, inter alia, the matters related to magnetic resonance imaging (MRI) considerations related to implantable medical devices (IMDs) intended to be used in the magnetic resonance (MR) environment. This includes both active implantable medical devices (AIMDs) and passive implantable medical devices (PIMDs). The authority mentions that each type of IMD system has its associated risk-benefit profile that needs to be addressed by the manufacturer. 

 

Recommendations in Brief 

First of all, the authority provides a brief overview of the recommendations to be taken into consideration for the aforementioned matters. In particular, it is stated that the products described in the present section of the guidance are complex systems composed of multiple components, hence, the composition of the system, as well as connections existing between its elements could impact significantly the overall safety and effectiveness. Hence, the authority expects medical device manufacturers to provide evidence demonstrating compliance with the applicable regulatory requirements such products are subject to. The authority additionally emphasizes that due to the nature of their materials, currently available AIMDs can only be marked as “MR conditional”, or “MR unsafe”, while PIMDs can be marked as “MR safe”, “MR conditional”, or “MR unsafe”. It is further explained that in case an IMD is marked as “MR conditional”, the appropriate conditions should be described in detail in the application submitted by a responsible party, as well as in documentation accompanying the device, including the instructions for use (IFU). At the same time, in the case of PIMDs, non-clinical data will be sufficient to demonstrate compliance with the respective Essential Principles. 

According to the guidance, concerning an AIMD, the applicant may provide post-market data, or the data collected in the course of clinical investigations, deriving from another jurisdiction where the product in question is already approved for marketing and use. To be admissible, such data should be represented in terms of addressing the aspects related to safety and performance in the context of MR conditional use. The applicants may also provide a literature review accompanied by a detailed description of the particular methods used. 

Safety in the MR Environment 

The guidance further describes in detail the concept of “safety” in the context of the MR environment in which the device is used. The approach followed by the authority is based on the applicable standard ASTM F2503-13, which provides that the MR environment stands for the physical space surrounding an MR magnet, which is affected by the static, gradient, and radiofrequency (RF) electromagnetic fields. The said standard also provides definitions of the aforementioned classification terms, namely: 

  • MR safe – an item that poses no known hazard resulting from exposure to any MR environment. As explained by the TGA, this applies to the products manufactured using materials that are electrically non-conductive, non-metallic, and non-magnetic. In the case of such devices, it will be sufficient to provide a rationale instead of test data. 
  • MR conditional – an item with demonstrated safety in the MR environment within defined conditions, where minimum requirements for demonstrating conditional MR safety requires consideration of the possible interactions between the device and the static, gradient, and radiofrequency fields present in the MR environment, and consideration of MR image artifacts from the implants. In such a case, it is important to address any potential hazards known to the manufacturer. 
  • MR Unsafe – an item that poses unacceptable risks to patients, medical staff, or other persons in the MR environment. 

 

Evidence Requirements 

The document also describes in detail the requirements evidence should meet to be admissible. As was mentioned before, the particular requirements to be applied would depend on whether the product in question is classified as “MR safe”, “MR conditional”, or “MR unsafe”. 

  • For products marked “MR safe”, the appropriate rationale is to be provided with references to the materials such products are made from. It should be clearly stated that the product poses no known hazards in MR environments. The authority also mentions that it is unlikely that any AIMD systems currently available would be designated as MR safe. 
  • In the case the product in question is marked “MR conditional”, the manufacturer should provide evidence demonstrating safety when the product is used under conditions specified by the manufacturer. As it was mentioned before, in the case of PIMD systems, non-clinical data will suffice. The authority also expects the manufacturer to provide a detailed description of the conditions of use. 

According to the guidance, additional information to be submitted concerning IMDs includes:

  • The technical specification of the device(s);
  • The components to which the device is paired when used clinically, for example, the pulse generator with its lead(s);
  • Scanning exclusion zones implemented;
  • A risk analysis and management document. 

In summary, the present TGA guidance provides additional clarifications regarding the classification of medical devices in terms of MR safety and highlights the key points to be considered when making the appropriate determination. The document also outlines the scope of information and documentation the applicant should provide depending on the classification of the product in question. 

 

Sources:

https://www.tga.gov.au/sites/default/files/clinical-evidence-guidelines-medical-devices.pdf 

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