1. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
FDA & CDRH, MR Critical Implants,
and
ASTM MR Safety Standards
Wolfgang Kainz, PhD
U.S. Food and Drug Administration - FDA
Center for Devices and Radiological Health - CDRH
Office of Science and Engineering Laboratories - OSEL
Division of Physics - DP

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Safety of MR critical implants Vienna, 09 JUL 2009
Purpose is to better understand
• FDA and CDRH
• RF induced heating of MR critical implants
• MR labeling of medical devices
Content
• FDA & CDRH
• MR critical implants
• MR critical medical devices
• Factors influencing RF induced heating
• SAR SAR
• The Virtual Family
• SAR distribution in anatomical models
• Safety aspects 1.5T vs. 3T
• B1rms as possible future measure for implant labeling
• ASTM MR Safety Standards
• Labeling

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Safety of MR critical implants Vienna, 09 JUL 2009
The U.S. Food and Drug
Administration is
• Scientific, Regulatory, Public Health Agency
• Mission is to protect and promote public health.
http://www.fda.gov/
• Authority to regulate medical devices
– Federal FD&C Act
• Established regulatory controls for medical
devices (May 28, 1976)
– 21 CFR Parts 800-1299
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4. mHH
Department ofcritical implants
Safety of MR Health & Human Vienna, 09 JUL 2009
Services
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Safety of MR critical implants Vienna, 09 JUL 2009
FDA Centers
and Regulated Products
• Food *
CDRH
• Drugs Center for Devices
and Radiological Health
• Medical Devices *
• Biologics CDER CBER
Center for Drugs and Center for Biologics and
• Animal Feed and Drugs Evaluation Research Evaluation Research
• Cosmetics
• Radiation-Emitting Products * FDA
• Combination Products
CVM CFSAN
(drug-device*, biologic-device*, Center for Center for Food Safety
drug-biologic) Veterinary Medicine and Applied Nutrition
– Primary mode of action NCTR
– RFD (Request for Designation) National Center
for Toxicological Research
Office of Regulatory Affairs (ORA)
is the lead office for all field activities.
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Safety of MR critical implants Vienna, 09 JUL 2009
Center Director
CDRH Dr. Daniel Schultz
Office of Device Evaluation ODE Office of Compliance (OC)
Office of Science and Office of Surveillance
Engineering Laboratories (OSEL) and Biometrics (OSB)
Office of Communication,
Education and Radiation Programs
Office of In Vitro Diagnostic
(OCER) *International Affairs Device Evaluation and Safety (OIVD)
http://www.fda.gov/cdrh/index.html
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Safety of MR critical implants Vienna, 09 JUL 2009
Regulatory Paradigm: Balancing
Risks and Benefits

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Safety of MR critical implants Vienna, 09 JUL 2009
MR critical implants (Guest Editorial in JMRI 26:450–451, 2007)
Definition:
• active implantable medical devices (AIMDs)
• semi-active implants, i.e., implants powered from outside of the body
• elongated metallic structures that are in the range of the critical length
• we currently believe that the critical length is in the range between the half wave
length and the wave length of the RF field inside the body, i.e., 25-50cm for 1.5T and
12-25cm for 3T
• currently no exclusion criteria for small implants exists

9. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
MR critical semi active implant
• Braingates Ischemic Stroke System

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Safety of MR critical implants Vienna, 09 JUL 2009
MR critical medical devices
Definition:
• active medical devices
• made of conductive material
• have critical masses or dimensions
• partially implanted and partially outside of the patient’s body
• are in electrical contact with the patient.
• electrically conductive leads (e.g., ECG leads) or probes in contact with the
patient

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Safety of MR critical implants Vienna, 09 JUL 2009
MR critical medical devices
• Electrode Arrays Cap

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Safety of MR critical implants Vienna, 09 JUL 2009
MR critical medical devices
• AutoLITT Probe from Monteris
RF Head Coil (Clear)
Probe Driver Follower
Probe
Head Fixation Device
PPI
Probe Driver
Commander
Interface Platform

13. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
MR critical medical devices
• AutoLITT Probe from Monteris
RF Head Coil
Probe Driver Follower
PPI
Probe
Probe Driver Commander Head Fixation Device
Interface
Platform
MRI Table

14. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
Factors influencing implant and medical device heating
responsible for implant and medical device heating are the local electric and magnetic
fields in the vicinity of the implant, induced by the radio frequency (RF) field
These local electric and magnetic fields depend on:
• scanner type, in particular the type of RF transmitting coil
• patient anatomy
• patient landmark
• implant location and orientation inside the patient; more specifically the implant
location in relation to the RF transmitting coil
• implant shape, implant size, and implant material
• RF exposure or the RF incident field: B1rms and the local electric fields produced by
the RF coil. The RF exposure is indirectly measured by estimating the patient’s whole
body averaged specific absorption rate (WB-SAR), the partial body averaged specific
absorption rate and the local peak (10g) averaged specific absorption rate (only for
local coils)

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Safety of MR critical implants Vienna, 09 JUL 2009
SAR SAR
• local peak SAR
• spatially averaged SAR
– averaged over certain mass of tissue or phantom material without specifying the
shape of the averaging volume; ICNIRP guidelines average over any 10g of
contiguous tissue
– averaged over certain mass of tissue or phantom material with specifying the
shape of the averaging volume; usually a cube
– averaged over parts of the body or parts of the phantom
– averaged over the whole body or the whole phantom = whole body averaged
SAR (WB-SAR); conservative WB-SAR estimate displayed on MR console
• temporally averaged SAR
– ICNIPR Guidelines and IEC 60601-2-33 average over any 6-min period
– IEC 60601-2-33 allows 3 fold increase of SAR within 10 seconds

16. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
Virtual Family
• Duke: male, 34yrs, 1.76m, 74kg
• Ella: female, 26yrs, 1.60m, 58kg
• Billie: female, 8yrs, 1.34m, 26kg
• Thelonious: male, 6yrs,1.07m, 17kg
• models are available for free
virtualfamily@itis.ethz.ch

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Safety of MR critical implants Vienna, 09 JUL 2009
Virtual Population
• 1 baby (coming in 2010)
• 5 children of both genders
(5 - 14 years; 13.5 - 18.4kg/m2)
• 1 men (23.1kg/m2)
• 1 female (22.7kg/m2)
• 1 obese male (35kg/m2)
• 1 pregnant female (24kg/m2)
• others on request

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Safety of MR critical implants Vienna, 09 JUL 2009
SAR distribution in different anatomical models at 1.5T

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Safety of MR critical implants Vienna, 09 JUL 2009
Sufficient Modeling Capabilities for AIMD Safety

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Safety of MR critical implants Vienna, 09 JUL 2009
Poser

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Safety of MR critical implants Vienna, 09 JUL 2009
SAR and MR critical implants - Conclusions:
• the SAR distribution in a patient is highly inhomogeneous and depends on the
anatomy, landmark and RF coil type
• the SAR distribution in the ASTM is also inhomogeneous and depends on the
landmark and RF coil type; however, the distribution can be calculated for each
landmark
• SAR distribution in ASTM phantom must be considered for placing the implant
• anatomical equivalent positioning of the implant in the ASTM phantom does not
reliable predict the implant heating in the patient
• worst case position in the ASTM must be guaranteed for conservative implant heating
assessment
• unresolved (IEC/ISO JWG AIMD MRI):
– standardized worst case implant positioning for 1.5T and 3T in the ASTM
phantom
– how to accurately relate the worst case heating in the ASTM phantom to the
possible heating in the patient; for the whole patient population Virtual Family

22. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
Safety aspects 1.5T versus 3T
• Force testing at higher field strengths is sufficient as long as the scanner with lower
field strength does not have a higher spatial static magnetic field gradient
• Torque testing needs to be done at the highest static field strength.
• The field distribution and the wavelength inside the patient at 3T are substantially
different than at 1.5T or at any higher or lower field strength.
• Therefore, RF induced heating can be substantially different at 3T and 1.5T.
• Important: RF induced heating testing at 3T, and subsequent 3T MR Conditional
labeling, does not necessarily guarantee safe scanning at 1.5T.
• The same is true for testing and labeling at 1.5T and then scanning at 3T.

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Safety of MR critical implants Vienna, 09 JUL 2009
B1rms could replace WB-SAR in the future for implant scanning
• The whole body averaged specific absorption rate (WB-SAR) displayed on MR
scanner consoles are conservative estimates intended to give an upper bound of the
WB-SAR induced in patients.
• The WB-SAR is intended only for patients and not for phantoms.
• This is supported by publications from Baker et al. and Nitz et al. and by the results of
the FDA initiated SAR Intercomparison protocol.
• The RF incident field, called the B1rms is the driving factor for the in the patient induced
electric and magnetic fields.
• B1rms will be displayed on the scanner console as required by IEC 60601-2-33 3rd Edt.
• B1rms will probably be used for labeling of implants in the future.

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Safety of MR critical implants Vienna, 09 JUL 2009
ASTM MR Test Methods
• ASTM F2052-02 for Measurement of Magnetically Induced Displacement Force on
Medical Devices in the MR Environment
• ASTM F2119-01 for Evaluation of MR Image Artifacts from Passive Implants
• ASTM F2182-02a for Measurement of Measurement of Radio Frequency Induced
Heating Near Passive Implants During MRI
• ASTM F2213-04 for Measurement of Magnetically Induced Torque on Medical
Devices in the MR Environment
• ASTM F2503-05 Standard Practice for Marking Medical Devices and Other Items for
Safety in the Magnetic Resonance Environment
• JWG TS on AIMDs

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Safety of MR critical implants Vienna, 09 JUL 2009
ASTM F2503 - Practice for Marking Items for Safety
• Intent:
– To prevent MR related accidents
– To correct problems with the use of historical terminology
– To introduce a new set of terms and MR icons consistent with current international safety
signs
• MR Safe
• MR Conditional
• MR Unsafe

26. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
FDA’s MR Conditional Labeling Suggestions
• Non-clinical testing has demonstrated that the MedDevABC up to a total length of XX mm is MR
Conditional. It can be scanned safely under the following conditions:
– Static magnetic field of X.X Tesla and Y.Y – Tesla (if applicable)
– Spatial gradient field of XXXX Gauss/cm or less
– Maximum whole-body-averaged specific absorption rate (SAR) of XX W/kg for XX minutes of
scanning. For landmarks (if applicable) XXXX (specify landmarks, if needed add drawing to
describe landmarks), the maximum whole-body-averaged specific absorption rate must be
less than XX W/kg.
– In a configuration where XXXX (describe the configuration for MR conditional labeling; e.g.,
legs apart, padding, maximum length of MedDevABC, etc).
– Use only, e.g. whole body coils, no transmitting local coils are allowed, receiving local coils
can be used.
• Add the MR conditional symbol to the label.
• The MedDevABC has not been evaluated for stent migration and heating in MR systems with field
strengths other than specified above. The heating and migration effect in the MR environment for
the MedDevABC in XXXX (specify other device configurations if applicable) is not known.

27. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
FDA’s MR Conditional Labeling Suggestions – Additional
Information
In an analysis based on non-clinical testing the MedDevABC was determined to
produce a potential worst-case temperature rise of XX°C for a whole body
averaged specific absorption rate (SAR) of 2 W/kg for XX minutes of MR
scanning in a XX Tesla, whole body MR system for a landmark in XXXX.
Temperature rises of the MedDevABC were measured in a non-clinical
configuration using a XXXX Whole Body active shield MR scanner using
software version XXXX and a phantom designed to simulate human tissue. The
phantom average SAR calculated for this non-clinical testing using calorimetry
was XX W/kg. When the MedDevABC was placed in a worst-case location within
the phantom, the maximal temperature rise was XX°C when the local SAR was
scaled to 2 W/kg.

28. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
FDA’s MR Conditional Labeling Suggestions – Additional
Information
• (For image quality labeling see also FDA Guidance on Establishing Safety and
Compatibility of Passive Implants in the Magnetic Resonance (MR) Environment)
• MR image quality may be compromised if the area of interest is in the exact same
area or relatively close to the position of the MedDevABC. The image artifact
extends approximately XX mm from the MedDevABC, both inside and outside (if
applicable) the device when scanned in non-clinical testing using echo and gradient
echo sequences as specified in ASTM F2119-01 in a XX Tesla, XXXX system, with
XXXX software, MR system with body radiofrequency coil. Therefore, it may be
necessary to optimize MR imaging parameters for the presence of this metallic
implant. The device lumen was always obscured during scanning (if applicable).
• Scanning at X.X Tesla and Y.Y Tesla may be performed immediately following the
implantation of the MedDevABC.
• We (name of the sponsor) recommend that the patient register the MR conditions
disclosed in this IFU with the MedicAlert Foundation or equivalent organization.
The MedicAlert Foundation can be contacted in the following manners:
Mail: MedicAlert Foundation International
2323 Colorado Avenue
Turlock, CA 95382
Phone: 888-633-4298 (toll free)
209-668-3333 from outside the US
Fax: 209-669-2450
Web: www.medicalert.org

29. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
FDA’s MR Conditional Labeling Suggestions – Implant Card
Non-clinical testing has demonstrated that the MedDevABC up to a total length of XX mm
is MR Conditional. It can be scanned safely under the following conditions:
• Static magnetic field of X.X Tesla and Y.Y – Tesla (if applicable)
• Spatial gradient field of XXXX Gauss/cm or less
• Maximum whole-body-averaged specific absorption rate (SAR) of XX W/kg for XX
minutes of scanning. For landmarks (if applicable) XXXX (specify landmarks, if
needed add drawing to describe landmarks), the maximum whole-body-averaged
specific absorption rate must be less than XX W/kg.
• In a configuration where XXXX (describe the configuration for MR conditional labeling;
e.g., legs apart, padding, maximum length of MedDevABC, etc).
• Use only whole body coils, no transmitting local coils are allowed, receiving local coils
can be used.
• Scanning at X.X Tesla and Y.Y Tesla may be performed immediately following the
implantation of the MedDevABC. The MedDevABC has not been evaluated for stent
migration and heating in MR systems with field strengths other than specified above.
The heating and migration effect in the MR environment for the MedDevABC in XXXX
(specify other device configurations if applicable) is not known.

30. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
Take home messages
• CDRH: getting safe and effective medical devices to market as quickly as possible
• Recognize MR critical implants and MR critical devices and scan only according
labeling
• Factors influencing implant heating: scanner type, RF coil, patient anatomy, patient
landmark, scan parameters, implant
• SAR SAR
• system estimated SAR is for patient safety only and not for phantoms
• SAR distribution in a patient is highly inhomogeneous
• MR safety testing in 1.5T and 3T scanners is complete different and cannot be related
to each other
• large variation of implant heating in different scanners needs to be considered
• B1rms could, and probably will, replace whole body averaged SAR for implant labeling
and scanning procedures
• Labeling: FDA guidance for passive implants, labeling for passive implants might not
be applicable to MR critical devices, labeling is an evolving subject
• although peer-reviewed and white papers published scanning procedures for
various active implantable medical devices (AIMDs), scanning of all patients
with implants should only be done according to approved labeling procedures

31. mHH
Safety of MR critical implants Vienna, 09 JUL 2009
Thank you for your brain work ...