Evaluation of Thermal Effects from Medical Devices on Human Tissue (DRAFT)
This guidance focuses on evaluating thermal effects of medical devices that produce tissue temperature changes (heating and/or cooling) as either an intended or unintended consequence of device use. This includes devices that: - Deliver radiofrequency, microwave, light, or other electromagnetic energy - Deliver ultrasound - Use electroporation - Produce temperature changes through contact - Have electrical components that can heat surrounding tissue
This is a draft guidance. Not for implementation.
What You Need to Know? 👇
What types of medical devices require thermal effects evaluation according to FDA guidance?
Devices that produce tissue heating/cooling including radiofrequency, microwave, light, ultrasound, electroporation devices, temperature-changing devices (hyperthermia, ablation, hypothermia, cryoablation), and devices with electrical components that may heat surrounding tissue during use.
When should phantom testing be used versus ex vivo or in vivo animal testing?
Phantom testing is suitable for minimal local temperature changes (≤6°C, resulting in ≤43°C absolute temperature) for short durations. Ex vivo testing is appropriate for higher temperatures with well-characterized effects. In vivo testing is needed for prolonged, regional, or systemic temperature changes.
What verification testing is required for device parameters before thermal effects assessment?
Bench testing must verify the device meets all labeled energy-related parameters across the full range of specifications with pre-defined acceptance criteria. This verification should be completed before conducting tissue effects and thermal energy spread assessments to ensure representative performance data.
How should the thermally affected tissue region be measured and reported?
Use histological stains (like H&E or viability stains) or tissue property changes (electrical impedance, elastic modulus, birefringence loss). Report dimensions including length, width, depth, and volume. Testing should be performed in triplicate at minimum, default, and maximum energy settings.
What computational models are acceptable for thermal effects evaluation?
Validated bioheat transfer models or empirical thermal models that accurately predict spatio-temporal temperature distribution for intended tissues. Models must include proper initial/boundary conditions, validation data, and demonstrate credibility per FDA’s computational modeling guidance requirements.
What labeling information must be included for thermal devices?
Include charts/graphs showing thermally affected tissue region dimensions (length, width, depth, volume) in relation to power settings and activation duration for different tissue types. This information helps users understand expected damage and facilitates safe device operation.
What You Need to Do 👇
Recommended Actions
- Determine appropriate testing methodology based on device characteristics and intended use
- Conduct verification testing of device parameters before thermal effects assessment
- Perform experimental assessment using appropriate model (phantom, ex vivo, in vivo)
- Document temperature-time history and dimensions of thermally affected tissue
- Validate any computational models used for evaluation
- Consider need for clinical testing if non-clinical results insufficient
- Develop comprehensive labeling with thermal effect dimensions and parameters
- Submit Pre-Submission to FDA for feedback on testing approach if needed
- Ensure testing covers full range of device specifications and use conditions
- Document scientific rationale for chosen testing methods and acceptance criteria
Key Considerations
Clinical testing
- Clinical data may be needed when non-clinical and animal studies are insufficient
- Studies should test full range of device parameters in intended population
- Must include safety measures and monitoring of target/non-target organs
- Results should document thermal injury and temperature-time history
Non-clinical testing
- Verification of device parameters through bench testing required
- Testing should cover full range of specifications with predefined acceptance criteria
- Must be done before assessment of tissue effects
- Deviations from acceptance criteria need scientific rationale
Labelling
- Include chart/graph showing dimensions of thermally affected tissue region
- Show relationship between power settings, activation duration and tissue types
- Document expected damage to facilitate safe use
Safety
- Assessment of tissue effects and thermal energy spread required
- Testing should evaluate minimum, average and worst-case temperature-time history
- Must allow tissue to return to baseline temperature
- Consider immediate and long-term tissue effects
Other considerations
- Phantom testing appropriate for minimal temperature changes (≤6°C)
- Ex vivo testing suitable for local temperature changes >43°C
- In vivo testing needed for prolonged or regional/systemic temperature changes
- Computational modeling can be used if properly validated
Relevant Guidances 🔗
- Electromagnetic Compatibility for Medical Devices and Accessories: Testing, Documentation, and Labeling Requirements
- Animal Testing for Medical Device Safety and Performance Evaluation
- Recommended Format and Content for Non-Clinical Bench Performance Testing in Medical Device Premarket Submissions
- Reporting of Computational Modeling and Simulation Studies in Medical Device Submissions
- Assessing the Credibility of Computational Modeling and Simulation in Medical Device Submissions
Related references and norms 📂
- IEC 60601-2-33 Ed.4.0: Medical electrical equipment - Part 2-33: Particular requirements for the basic safety and essential performance of magnetic resonance equipment for medical diagnosis