Criteria for Significant Risk Investigations of Magnetic Resonance Diagnostic Devices
This guidance outlines the criteria for determining when investigations of Magnetic Resonance Diagnostic Devices (MRD) are considered significant risk, requiring FDA approval of an Investigation Device Exemption (IDE). It applies to class II devices under 21 CFR 892.1000, including Magnetic Resonance Imaging Systems and Magnetic Resonance Spectroscopic Systems.
What You Need to Know? 👇
What are the main criteria that make an MRI device study significant risk according to FDA guidance?
FDA considers MRI studies significant risk when they exceed specific thresholds for static magnetic field strength, specific absorption rate (SAR), gradient field changes causing nerve stimulation, or sound pressure levels above 140 dB peak or 99 dBA with hearing protection.
What static magnetic field limits apply to different patient populations in MRI studies?
For adults, children, and infants over 1 month old, the limit is 8 tesla. For neonates (infants 1 month or younger), the significantly lower limit is 4 tesla due to their increased vulnerability to magnetic field effects.
What are the SAR limits that trigger significant risk classification for MRI devices?
Whole body SAR exceeding 4 W/kg averaged over 15 minutes, or head SAR exceeding 3.2 W/kg averaged over 10 minutes are considered significant risk thresholds requiring FDA IDE approval for clinical studies.
Do MRI clinical studies always require FDA IDE approval after 510(k) clearance?
No, after FDA determines substantial equivalence through 510(k) clearance, clinical studies conducted within the cleared indications are exempt from IDE requirements, though they must still comply with IRB and informed consent regulations.
What sound pressure levels make MRI studies significant risk according to FDA criteria?
Peak unweighted sound pressure levels greater than 140 dB or A-weighted RMS sound pressure levels exceeding 99 dBA with hearing protection in place are considered significant risk thresholds for MRI studies.
When do gradient field changes in MRI require significant risk study classification?
Any time rate of change of gradient fields (dB/dt) sufficient to produce severe discomfort or painful nerve stimulation qualifies the study as significant risk, requiring full IDE approval rather than abbreviated requirements.
What You Need to Do 👇
Recommended Actions
- Assess planned operating conditions against the specified limits for magnetic field, SAR, gradient fields, and sound pressure
- If any operating condition exceeds the specified limits, prepare for IDE submission
- Implement appropriate safety controls and monitoring for all specified parameters
- Ensure compliance with IRB and informed consent requirements
- Contact FDA for clarification on local SAR criteria if needed
- Review complete risk assessment beyond just operating conditions
- Maintain documentation of operating conditions and safety measures
- Establish protocols for monitoring and maintaining operating conditions within specified limits
Key Considerations
Clinical testing
- Studies requiring IDE approval must comply with institutional review boards (21 CFR Part 56) and informed consent (21 CFR Part 50)
- After substantial equivalence determination, clinical studies conducted within approved indications are exempt from IDE requirements
Safety
- Main static magnetic field limits:
8 tesla for adults, children, and infants > 1 month
4 tesla for neonates (≤ 1 month)
- Specific Absorption Rate (SAR) limits:
- Whole body: > 4 W/kg averaged over 15 minutes
- Head: > 3.2 W/kg averaged over 10 minutes
- Gradient fields: Any rate of change causing severe discomfort or painful nerve stimulation
- Sound pressure limits:
- Peak unweighted level > 140 dB
- A-weighted RMS level > 99 dBA with hearing protection
Other considerations
- Operating conditions beyond these limits qualify as significant risk under 21 CFR 812.3(m)(4)
- Other aspects of the study may involve significant risks requiring IDE approval regardless of operating conditions
Relevant Guidances 🔗
- Testing and Labeling of Medical Devices for Magnetic Resonance (MR) Environment Safety and Compatibility
- Assessment of Radiofrequency-Induced Heating in Multi-Configuration Passive Medical Devices for MR Conditional Labeling
- Premarket Notification Requirements for Magnetic Resonance Diagnostic Devices
Related references and norms 📂
- 21 CFR 892.1000: Magnetic Resonance Diagnostic Device
- 21 CFR Part 812: Investigational Device Exemptions
- 21 CFR Part 56: Institutional Review Boards
- 21 CFR Part 50: Protection of Human Subjects