The Future Of Mri Safety W Kainz 13 Jul2009

mHH
The Future of MRI Safety 14 JUL 2009

The Future of MRI Safety
Challenges From a Regulatory Perspective

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

mHH

Purpose of this talk

to provide a regulatory perspective on MRI safety

and
to provoke thinking out of the box

mHH
Content

• FDA & CDRH
• MRI Safety: The Present & The Future
– Define MRI safety
– How to achieve it
– Limits
– Effects of E, H and EM fields on the patient
– MR accidents and injuries
– Fetal imaging
– MR critical implants and MR critical medial devices, 1.5T vs. 3T, B1 vs. SAR, ASTM standards
• Thoughts for The Future

mHH

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
4

mHH

Department of MRI Safety
The Future Health & Human 14 JUL 2009
Services

5

mHH

FDA Centers
and Regulated Products
• Food *
CDRH
Center for Devices
• Drugs and Radiological Health
• Medical Devices * CDER CBER
Center for Drugs and Center for Biologics and
• Biologics Evaluation Research Evaluation Research

• Animal Feed and Drugs FDA
• Cosmetics CVM CFSAN
• Radiation-Emitting Products * Center for Center for Food Safety
Veterinary Medicine and Applied Nutrition
• Combination Products NCTR
(drug-device*, biologic-device*, National Center
for Toxicological Research
drug-biologic)
– Primary mode of action Office of Regulatory Affairs (ORA)
– RFD (Request for Designation) is the lead office for all field activities. 6

mHH

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,
Office of In Vitro Diagnostic
Education and Radiation Programs
(OCER) *International Affairs
Device Evaluation and Safety (OIVD)

http://www.fda.gov/cdrh/index.html

mHH

Regulatory Paradigm: Balancing
Risks and Benefits
… while
Getting safe and
ensuring that
effective devices
devices
to market as
currently on the
quickly as
market remain
possible…
safe and
effective.
Helping the public get science-based accurate information about
medical devices and radiological products needed to improve
health.

mHH
FDA Regulatory approach to MRI

• FDA Considers MRI a Class II medical device listed under CFR Section
892.1000 "Magnetic Resonance Diagnostic Device"
• 510(k) process to evaluate Safety & Effectiveness
• Two Guidance documents:
2003: Criteria for Significant Risk Investigations of Magnetic Resonance
Diagnostic Devices
http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm072686.htm

1998: Guidance for the Submission Of Premarket Notifications for
Magnetic Resonance Diagnostic Devices
http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm073817.htm

mHH
Upward trend of static magnetic field

• 3T systems cleared for use starting in 1999 in USA
• Trend towards higher field systems
– In 2006, 90% of newly installed units ≥1.5T
– In 2008 ~700 3T installations
– ISMRM 2009 report > 20 7.0T Siemens Installations world wide
(none cleared by FDA)
• ~15 FDA Submissions each year since 2000

mHH
Global sales trends: 1.5T – 3T – Open MRI

mHH

Overall goal for MRI safety

safe scanning for the whole patient population and
high resolution
high contrast
fast
clear tissue identification
price
time to market

mHH

How to achieve RF MRI safety?

1. to relate WB-SAR to local SAR and to local tissue temperature for:
a) the whole patient population
b) all patient locations, positions, and postures
c) all applicable MRI systems
2. relate local tissue temperature to thermal thresholds for adverse
health effects for the whole patient population
3. define safe MRI scanning parameters and procedures to avoid
adverse health effects for the whole patient population
4. EM and bio-heat modeling in multiple full body anatomically correct
models Virtual Patient

mHH

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

mHH

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

mHH

SAR ≠ SAR ΔT E rms
2
SAR = c SAR = σ
Δt t =0 ρ
• 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

mHH

Criteria for adverse health effects: localized heating
CEM 43 values for various tissues (Goldstein et al. 2003, CEM endpoints: assess damage have included
death, grossly assessable damage as well as histologic analysis (both qualitative and quantitative methods).

• most sensitive
– testes and brain ........................................................................................< 20
– blood-brain barrier break down ................................................................. ~ 15
– scattered neuronal death ..........................................................................~ 2
– conjunctiva, bone marrow and kidney ....................................................... < 20
• moderately sensitive
– bowel, retina, cornea, skin and prostate ................................................... 21 - 40
• relatively insensitive
– anterior chamber of the eye, choroid, ciliary body, lens, fat, muscle and peripheral nerves
....................................................................................................... 40 - 80

mHH

Criteria for adverse health effects: tissue damage
• tissue damage will occur ...................................................................... > 80

• most sensitive tissue (scattered neuronal death) CEM 43 of 2 corresponds
to:
– 17h at 38ºC
– 4h at 39ºC
– 1h at 40ºC

mHH
FDA limits for Static Field
• No specific FDA limit, only defined by 510(k) and PMA process for
Medical Devices
• “Significant Risk” devices require “Investigational Device Exemption” (IDE)
for Clinical Studies, such as for 9.4T
• Limits for non-significant risk studies
– 4T for neonates 1 month or younger
– 8T for older subjects
• Up to now only 3.0T devices cleared for marketing as a part of 510(k)
process, >3T PMA or 510k (clarification during pre-IDE)

mHH

FDA SAR limits for significant risk investigations

BODY SITE EXPOSURE type TIME SAR
(min) (W/Kg)

Whole Body Averaged over 15 4

Head Averaged over 10 3

Head or Torso per /gm of tissue 5 8

Extremities per /gm of tissue 5 12

mHH
Bio-effects of Static Field
• Cell Effects: Numerous studies with a range of subtle effects
– orientation, growth, metabolism, gene expression
• Animal data
– avoidance behavior in mazes
– no adverse effects on reproduction and growth has been established
– need more studies at > 1Tesla
• human acute effects: vertigo, magnetophosphenes, metallic taste
• insufficient evidence to draw conclusions from studies on cancer and
reproduction (Dini et al., Schenk et al. JMRI)

mHH
Acute effects in ultra-high fields

Static magnetic field effects (up to 8 T) on human subjects related to
magnetic resonance imaging systems
Chakeres and De Vocht
Progress in Biophysics and Molecular Biology 87 (2005) 255–265

Safety of Human MRI at Static Fields Above the FDA 8T Guideline:
Sodium Imaging at 9.4T Does Not Affect Vital Signs or Cognitive
Ability
Atkinson, Renteria, Burd, Flannery, Pliskin, and Thulborn
Journal of Magnetic Resonance Imaging (2007) 26:1222–1227

mHH
Human Exposure to 9.4T

• Questions:
– Does a static magnetic field of 9.4T affect
human health?
– What discomforts are experienced by
exposure to 9.4T static magnetic field?

• Vital signs and cognitive ability measured
before and after exposure to a 9.4T MR 9.4T static magnetic field
scanner and a zero field mock MR 80 cm bore
scanner 80 mT/m head gradient set
Full proton and non-proton capabilities
– 25 healthy normal volunteers Real-time SAR monitoring on six exciter
– 12 male, 13 female outputs
Only the static field is outside of the
– 18-63 years of age (mean 30.8y)
current non-significant risk guidelines

mHH
Human Exposure to a 9.4T - Results
• During exposure to 9.4T MR scanner N
– Vertigo or lightheadedness 18
– Sleepiness 8
– Temperature change 4
– Metallic taste 6
• 2 cooler, 1 felt a draft, 1 warmer
– Nausea 2
– Muscle twitching or tingling 2
• 1 during imaging
– Visual disturbance 1
– Anxiety 1

• During exposure to the mock MR scanner N
– Sleepiness 12
– Temperature change 4
• 1 cooler, 3 warmer
– Anxiety 3
– Lightheadedness 1
– Discomfort due to acoustic noise 1

mHH
Representative ECG Waveforms
• expected distortions observed at iso-center of 9.4T
scanner
• ECG waveforms returned to baseline outside the
9.4T static magnet field

• such effects are consistent with previous results
– Kangarlu, et al. MRM 1999
– Chakeres, et al. JMRI 2003
– Chakeres, et al. Progress in Biophysics and Mol. Bio. 2005
– Kangarlu, et al. Concepts in Mag. Res. 2000
• altered electrical signals read by the ECG electrodes
as a consequence of motion of conductive structures
in the Static field.
MHD Project

mHH
Indirect Effects of Strong Static Magnetic Field

• Ferromagnetic Accidents
• Large objects: chairs, gas tanks, medical devices
• Small objects: paper clips & surgical clamps

• Cryogen Accidents
Leads to : Air replacement with helium
(Need for adequate venting and door design)

mHH
Ferromagnetic objects: need for screening
buffing machines pacemakers
chest tube stands pagers
clipboards (patient charts) paper clips
gurneys pens and pencils
hairpins IV poles
hearing aids prosthetic limbs
identification badges shrapnel
insulin pumps sandbags (with metal filings)
keys steel shoes
medical gas cylinders stethoscopes
mops scissors
nail clippers and nail files staples
oxygen cylinders tools
pulse oximeters vacuum cleaners
Cell phones watches
wheelchairs

mHH
Floor waxer wants an MRI scan!

mHH
Cryogen accidents
MRI Explosion
• Took place in Salisbury, Maryland
in 2006.
• A MRI exploded while preparing it
for transfer.
• Initial reports say that the explosion
was due to the venting process.
• Later reports say that there was a
buildup of ice in the venting lines and
around the pressure sensor that
would release the pressure if it got to
high.

mHH
Danger: "Sandbag" in the MRI Room
Beverly Albrecht Gallauresi, RN, MPH, and Terry Woods, PhD
(Article reprinted from December Nursing 2008, Volume 38, Issue 12)

A PATIENT UNDERWENT magnetic resonance imaging (MRI) while
she had a sandbag on her groin to help facilitate hemostasis after a
procedure that involved femoral artery puncture. The staff assumed
that the bag contained only sand. As the study began, the sandbag
was pulled into the MRI coil, damaging the system. Fortunately, the
patient wasn’t injured, according to the report.

mHH
Detection of Ferromagnetic Objects

Metrasens developed the first
commercially available
Ferromagnetic detection product
in 2003

CAUTION:
Even Non-Ferromagnetic
conductors can cause heating

mHH
How SAR is handled in MRI

• console provides conservative estimates of SAR for each pulse
sequence
• SAR values can be modified by decreasing flip angle, number of
pulses or using alternate pulse sequence
• system console will limit scanning to first level SAR before the start of
the scan
• for high field systems FDA considers SAR controlling software as
“moderate level of concern” as per MRI Guidance document

mHH

RF Injury: MAUDE 1998-2007
MRI Burns
45
40

35
30

Events
25
20

40 15

35 10

30 5

25 0
Events

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
20
Year
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Primary Burn Location

mHH
Potential causes for heating and burns

• Skin contact with the bore: local E-fields
• Conductive loop: B1-Induced currents, E-field induced currents
• Hot spots within the patient
• Cables, guidewires and electrodes
• Conductive implants: passive and AIMDs

mHH
Events

U

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30
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The Future of MRI Safety

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14 JUL 2009

mHH
Other Hazards: Contrast Agents

• Approximately 30% of MRI procedures use an injection of i.v. contrast
agents
• Nephrogenic Systemic Fibrosis found in patients with endstage of renal
disease

“NOT A HAZARD FOR NON-CONTRAST MRI”

mHH
Other Hazards

• Transdermal patches
• Tattoos (ferromagnetic effect) and cosmetics
• Conductive Implants
– Stents
– coils
• Active medical devices
– Pumps
– Pacemakers, ICDs, neurostimulators, …

mHH
Risks of and Guidelines for Fetal MRI
• Potential safety risks
– Contrast agents Teratogenic / Toxic effects ?
– Static magnetic field Teratogenic effects ?
– Radio frequency field Fetal tissue heating ?
– Gradient field (noise) Damage to the auditory pathways ?

• FDA’s position is that the safety of magnetic resonance
examinations has not been completely established.
• Clinical Practice (Not FDA regulated): Need to balance
immediate benefits versus undefined risk

mHH
Pregnant woman models

Placenta
Fetus

Liquid
Uterus

Bone

Bladder

mHH
Pregnant woman models

mHH
Simulation steps
Step 2: Prepare Pregnant
Step 1: Create and tune the
Woman Models for
MRI coil
simulations

Step 3: Load coil with
pregnant woman and run
simulation.

mHH
Tune birdcage coil to pregnant woman model

Capacitor vs. Month For Loaded Coil

1.6
C acito [p ]
r F

1.5
ap

1.4

1.3
1 2 3 4 5 6 7 8 9
Month of Pregnancy

mHH

Simulation setup

74.316 cm
74.3 cm
74.3[cm]

67.0 [cm]
67.0
67.0 cmcm

64 & 128 MHz
Normal & first level controlled modes

mHH
SAR (W/Kg) ΔT (oC)
Month 1
Month 9

mHH
Results 64 MHz -- Normal mode

mHH
Results 64 MHz -- First level controlled mode

mHH
Results summary for fetus tissue only
Fetus 64 MHz 128 MHz
Normal First level Normal First level controlled
Mode controlled mode Mode mode
Not Not
SAR limit Exceeded Not exceeded
exceeded exceeded
Month 1-4
Temperature Not Not
Exceeded Not exceeded
limit exceeded exceeded
Not Not
SAR limit Exceeded Not exceeded
exceeded exceeded
Month 5-9
Temperature Not Not
Exceeded Not exceeded
limit exceeded exceeded

• Based on the results of this study, we recommend not performing MRI procedures
on pregnant women using the first level controlled mode.

• SAR and temperature rise distributions are quite different at the two MRI operating
frequencies. Such variation is caused by the different electric field distributions
generated by MRI coils at these two frequencies and it is also related to the difference
in dielectric parameters at these two frequencies.

mHH

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

mHH

MR critical semi active implant

• Braingates Ischemic Stroke System

mHH
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

mHH


• Electrode Arrays Cap

mHH


• AutoLITT Probe from Monteris

RF Head Coil (Clear)

Probe Driver Follower

Probe

Head Fixation
Device

PPI

Probe Driver
Commander

Interface Platform

mHH
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)

mHH

SAR distribution in different anatomical models at 1.5T

mHH
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 phantom 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

mHH
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.

mHH

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.

mHH

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

mHH

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

mHH

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.

mHH

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.

mHH

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.

mHH
Summary
• MRI is here and will stay: ~40 million MRI scans are performed in US every year
• long term effects of exposure (electromagnetic) are vastly overshadowed by the
immediate benefits
• MRI is safe for the patient and provider if proper safety precautions are taken
• future MRI systems with different architectures, high fields, parallel transmit coils
may warrant further vigilance
• SAR ≠ SAR, needs to be made very clear to user, clear and unique names for all
SAR values, e.g., SAR-WB, SAR-10g, SAR-organ, SAR-tissue, …
• B1rms should and will complement SAR values as safety measure

mHH
Thoughts for The Future I
• higher field strengths will results in higher SAR inhomogeneity
– limiting safety factor will be hot spots
– currently 60601-2-33 does not limit local SAR and local temperature increase for body coil
– coil design to increase SAR homogeneity: coil optimization is an antenna design problem,
automatic and semi-automatic antenna optimization methods are available
– whole patient population, including posture variations, need to be included: babies, children,
obese patients, pregnant women, …
– needed computational methods and anatomical computer models are available for coil
optimization
• higher SAR = higher SNR is possible if:
– tissue damage and thermal damage thresholds are thoroughly and scientifically sound
assessed and understood; temperature measurements using phase thermometry or other
methods to control and limit temperature increase
– online temperature measurements allow patient specific SAR optimization
– on-the-fly SAR calculations (fast FDTD simulations without segmentation, Paolo Faraceyz et al. An
automated method for mapping human tissue permittivities by MRI in hyperthermia treatment planning)

mHH
Thoughts for The Future II
• Interventional procedures
– interventional procedure mode
– interventional safety assessment: occupational health
– safety of interventional medical devices
– Cooperation and collaboration with MR interventional development companies to assure
safety and efficacy. Such collaborations smooth FDA approval process.
• Implants
– implant mode to limit gradients and B1, limiting gradient and B1 field is technically feasible
– simplify scanning assessment for implant patients
– automatic implant detection using e.g., RFID systems and automatic adjustment of implant
mode parameters
– develop implant sequences to minimize image artifacts

mHH
Thoughts for The Future III
• Computational method improvements
– body core temperature calculations
– SAR averaging and temperature averaging tissue and volume specific
• Standardization needs
– Criteria for adverse health effects: localized heating, cumulative exposure
– infants and pregnant woman MRI
– need for new safety concept: adapted CEM concept combined with well established thermal
damage thresholds
• Be ready for >3T PMA (or 510k)
– have sufficient, sound and convincing safety data available for FDA
– such safety data has most weight published if in peer-reviewed literature and done in
collaborations with academia experts in the field
– efficacy data will be easier to collect and provide for a FDA application
– occupational safety assessment

mHH
Thoughts for The Future IIII
• Research opportunities:
– tissue damage
– hot spot warning feature collaboration with Prof. Tommy Vaughan Univ.
Minnesota: to measure non-invasively temperature increase in humans using phase shift
thermometry
– distortion free sequences or better combination methods with distortion free imaging
modalities (like CT), needed for e.g., neuro-surgical planning procedures or for implants
– in 30% of MR burns the cause is unknown: investigation of the cause and develop counter
measures
– anisotropic tissue identification
– automatic tissue identification and segmentation e.g., brain nerve fiber orientation and
visualization
• Safety and efficacy of combination imaging modalities
– CT, PET, …

mHH
Take home messages
• it is important to be ready for:
– high field MR safety
– >3T PMA
• methods and models for RF safety assessment are available
• conduct safety research to completely understand and mitigate high field RF safety
• investigational MRI procedures are here and will increase
• reconsider approach to implant safety
• collaboratively in peer-reviewed journals published data is helpful for smooth FDA
review

mHH
Thank you for your brain work ...

The Future Of Mri Safety W Kainz 13 Jul2009

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