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U.S. Department of Health and Human Services

Medical Devices

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Guidance for Industry and FDA Staff: Criteria for Significant Risk Investigations of Magnetic Resonance Diagnostic Devices

PDF Printer VersionDocument issued on: July 14, 2003

This document supersedes “Guidance for Magnetic Resonance Diagnostic Devices – Criteria for Significant Risk Investigations” issued on September 29, 1997

For questions regarding this document, contact Loren A. Zaremba, Ph.D., at 240-276-3666 or by e-mail at loren.zaremba@fda.hhs.gov


U.S. Department of Health and Human Services
Food and Drug Administration
Center for Devices and Radiological Health

Radiological Devices Branch
Division of Reproductive, Abdominal, and Radiological Devices
Office of Device Evaluation


Contains Nonbinding Recommendations


Public Comment:

Written comments and suggestions may be submitted at any time for Agency consideration to Division of Dockets Management, Food and Drug Administration, 5630 Fishers Lane, Room 1061, (HFA-305), Rockville, MD, 20852. When submitting comments, please refer to the exact title of this guidance document. Comments may not be acted upon by the Agency until the document is next revised or updated.

Additional Copies

Additional copies are available from the Internet or to receive this document by fax, call the CDRH Facts-On-Demand system at 800-899-0381 or 301-827-0111 from a touch-tone telephone. Press 1 to enter the system. At the second voice prompt, press 1 to order a document. Enter the document number (793) followed by the pound sign (#). Follow the remaining voice prompts to complete your request.

Guidance for Industry and FDA Staff

Criteria for Significant Risk Investigations of Magnetic Resonance Diagnostic Devices

This guidance represents the Food and Drug Administration's (FDA's) current thinking on this topic. It does not create or confer any rights for or on any person and does not operate to bind FDA or the public. You can use an alternative approach if the approach satisfies the requirements of the applicable statutes and regulations. If you want to discuss an alternative approach, contact the FDA staff responsible for implementing this guidance. If you cannot identify the appropriate FDA staff, call the appropriate number listed on the title page of this guidance.


This guidance describes the device operation conditions for magnetic resonance diagnostic devices that FDA considers significant risk for the purposes of determining whether a clinical study requires Agency approval of an Investigation Device Exemption (IDE). Magnetic resonance diagnostic devices are class II devices described under 21 CFR 892.1000. The product codes for these devices are:

LNH Magnetic Resonance Imaging System
LNI Magnetic Resonance Spectroscopic System

This guidance supersedes Guidance for Magnetic Resonance Diagnostic Devices - Criteria for Significant Risk Investigations, issued September 29, 1997. We have revised our recommendation for the main static magnetic field strength, increasing it to 8 tesla for most populations. This is based on ongoing experience in the field and numerous literature reviews.1,2

FDA's guidance documents, including this guidance, do not establish legally enforceable responsibilities. Instead, guidances describe the Agency's current thinking on a topic and should be viewed only as recommendations, unless specific regulatory or statutory requirements are cited. The use of the word should in Agency guidances means that something is suggested or recommended, but not required.

The Least Burdensome Approach

We believe we should consider the least burdensome approach in all areas of medical device regulation. This guidance reflects our careful review of the relevant scientific and legal requirements and what we believe is the least burdensome way for you to comply with those requirements. However, if you believe that an alternative approach would be less burdensome, please contact us so we can consider your point of view. You may send your written comments to the contact person listed in the preface to this guidance or to the CDRH Ombudsman. Comprehensive information on CDRH's Ombudsman including ways to contact him, can be found on the Internet.

Studies of Magnetic Resonance Diagnostic Devices

If a clinical study is needed to demonstrate substantial equivalence, i.e., conducted prior to obtaining 510(k) clearance of the device, the study must be conducted under the IDE regulation (21 CFR Part 812). FDA believes that a magnetic resonance diagnostic device used under any one of the operating conditions listed below is a significant risk device as defined in 21 CFR 812.3(m)(4) and, therefore, that studies involving such a device do not qualify for the abbreviated IDE requirements of 21 CFR 812.2(b). In addition to the requirement of having an FDA-approved IDE, sponsors of significant risk studies must comply with the regulations governing institutional review boards (21 CFR Part 56) and informed consent (21 CFR Part 50).

Significant Risk Magnetic Resonance Diagnostic Devices

You should consider the following operating conditions when assessing whether a study may be considered significant risk:

  • main static magnetic field
  • specific absorption rate (SAR)
  • gradient fields rate of change
  • sound pressure level

Generally, FDA deems magnetic resonance diagnostic devices significant risk when used under any of the operating conditions described below.

Main Static Magnetic Field

Population Main static magnetic field greater than (tesla)
adults, children, and infants aged > 1 month 8
neonates i.e., infants aged 1 month or less 4

Specific Absorption Rate (SAR)

Site Dose Time (min)
equal to or greater than:
whole body averaged over 15 4
head averaged over 10 3
head or torso per gram of tissue 5 8
extremities per gram of tissue 5 12

Gradient Fields Rate of Change

Any time rate of change of gradient fields (dB/dt) sufficient to produce severe discomfort or painful nerve stimulation

Sound Pressure Level

Peak unweighted sound pressure level greater than 140 dB.

A-weighted root mean square (rms) sound pressure level greater than 99 dBA with hearing protection in place.

These criteria apply only to device operating conditions. Other aspects of the study may involve significant risks and the study, therefore, may require IDE approval regardless of operating conditions. See Blue Book Memorandum entitled Significant Risk and Non-significant Risk Medical Device Studies, for further discussion.

After FDA determines that the device is substantially equivalent, clinical studies conducted in accordance with the indications reviewed in the 510(k), including clinical design validation studies conducted in accordance with the quality systems regulation, are exempt from the investigational device exemptions (IDE) requirements. However, such studies must be performed in conformance with 21 CFR 56 and 21 CFR 50.

1Kangarlu A, Burgess RE, Zu H, et al. Cognitive, cardiac and physiological studies in ultra high field magnetic resonance imaging. Magnetic Resonance Imaging, 1999;17:1407-1416.

2Schenck John F, Safety of strong, static magnetic fields. Journal of Magnetic Resonance Imaging, 2000;12:2-19.