the future of mri safety w kainz 13 jul2009

The Future of MRI Safety 14 JUL 2009mHH

The Future of MRI SafetyChallenges From a Regulatory Perspective

Wolfgang Kainz, PhD

U.S. Food and Drug Administration - FDACenter for Devices and Radiological Health - CDRH

Office of Science and Engineering Laboratories - OSELDivision of Physics - DP


Purpose of this talk

to provoke thinking out of the box

to provide a regulatory perspective on MRI safety

and


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


4

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


5

Department of Health & Human Services


6

FDA Centers and Regulated Products

• Food• Drugs• Medical Devices *• Biologics• Animal Feed and Drugs• Cosmetics • Radiation-Emitting Products *• Combination Products

(drug-device*, biologic-device*, drug-biologic)– Primary mode of action– RFD (Request for Designation)

CDERCenter for Drugs andEvaluation Research

CVMCenter for

Veterinary MedicineNCTR

National Centerfor Toxicological Research

CFSANCenter for Food Safetyand Applied Nutrition

CBERCenter for Biologics and

Evaluation Research

CDRHCenter for Devices

and Radiological Health

FDA

*

Office of Regulatory Affairs (ORA)is the lead office for all field activities.


Center DirectorDr. Daniel Schultz

Office of Device Evaluation ODE Office of Compliance (OC)

Office of Science and Engineering Laboratories (OSEL)

Office of Surveillanceand Biometrics (OSB)

Office of Communication,Education and Radiation Programs

(OCER) *International Affairs

Office of In Vitro Diagnostic Device Evaluation and Safety (OIVD)

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

CDRH


Regulatory Paradigm: Balancing Risks and Benefits

Getting Getting safe and safe and effective deviceseffective devicesto market as to market as quickly as quickly as possiblepossible……

…… while while ensuring that ensuring that

devices devices currently on the currently on the

market remain market remain safe and safe and

effectiveeffective..Helping the public get Helping the public get sciencescience--based accurate informationbased accurate information about about

medical devices and radiological products needed to improve medical devices and radiological products needed to improve health.health.


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 forMagnetic Resonance Diagnostic Devices

http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm073817.htm


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


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


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


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


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 [email protected]


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


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

0=ΔΔ

=tt

TcSARρ

σ2

rmsESAR =


Criteria for adverse health effects: localized heatingCEM 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


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


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)


FDA SAR limits for significant risk investigations

BODY SITE EXPOSURE type TIME (min)

SAR (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


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)


Acute effects in ultra-high fields

Static magnetic field effects (up to 8 T) on human subjects related to magnetic resonance imaging systemsChakeres and De VochtProgress 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 AbilityAtkinson, Renteria, Burd, Flannery, Pliskin, and ThulbornJournal of Magnetic Resonance Imaging (2007) 26:1222–1227


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 scanner and a zero field mock MR scanner

– 25 healthy normal volunteers– 12 male, 13 female– 18-63 years of age (mean 30.8y)

9.4T static magnetic field80 cm bore

80 mT/m head gradient setFull proton and non-proton capabilities

Real-time SAR monitoring on six exciter outputs

Only the static field is outside of the current non-significant risk guidelines


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


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


Indirect Effects of Strong Static Magnetic Field

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

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


buffing machineschest tube standsclipboards (patient charts)gurneyshairpinshearing aidsidentification badgesinsulin pumpskeysmedical gas cylindersmopsnail clippers and nail filesoxygen cylinderspulse oximetersCell phones

pacemakerspagerspaper clipspens and pencilsIV polesprosthetic limbsshrapnelsandbags (with metal filings)steel shoesstethoscopesscissorsstaplestoolsvacuum cleanerswatcheswheelchairs

Ferromagnetic objects: need for screening


Floor waxer wants an MRI scan!


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.


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.

Danger: "Sandbag" in the MRI Room


Detection of Ferromagnetic Objects

Metrasens developed the first commercially available Ferromagnetic detection product in 2003

CAUTION: Even Non-Ferromagnetic

conductors can cause heating


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


RF Injury: MAUDE 1998-2007

0

5

10

15

20

25

30

35

40

Elbow

ArmTo

rsoFo

rearm Han

dTh

ighSho

ulder

Leg

Unkno

wnHea

d

HipKne

eW

rist

Feet

Mouth

Buttoc

ksPelv

is

Primary Burn Location

Eve

nts

MRI Burns

0

5

10

15

20

25

30

35

40

45

1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Year

Even

ts


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


RF Injury: MAUDE 1998-2007

0

10

20

30

40

50

60

70

Unkno

wnBo

re C

onta

ctLa

ck of

Pad

ding

Fore

ign O

bject

Skin-

to-S

kin

Coil C

onta

ctRF

Burn

/RF

Loop

Defec

tive E

quipm

ent

Root Cause

Even

ts


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”


Other Hazards

• Transdermal patches

• Tattoos (ferromagnetic effect) and cosmetics

• Conductive Implants

– Stents

– coils

• Active medical devices

– Pumps

– Pacemakers, ICDs, neurostimulators, …


Risks of and Guidelines for Fetal MRI

• Potential safety risks– Contrast agents– Static magnetic field – Radio frequency field– Gradient field (noise)

• 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

Teratogenic / Toxic effects ?Teratogenic effects ?Fetal tissue heating ?Damage to the auditory pathways ?


Fetus

Liquid

Placenta

Uterus

Bladder

Bone

Fetus

Liquid

Placenta

Uterus

Bladder

Bone

Pregnant woman models


Pregnant woman models


Step 1: Create and tune the MRI coil

Step 2: Prepare Pregnant Woman Models for simulations

Simulation steps

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


Tune birdcage coil to pregnant woman model

Capacitor vs. Month For Loaded Coil

1.3

1.4

1.5

1.6

1 2 3 4 5 6 7 8 9

Month of Pregnancy

Cap

acito

r [pF

]


Simulation setupSimulation setup

74.316 [cm]

67.0 [cm]

74.316 [cm]74.316 [cm]

67.0 [cm]

74.3 cm

67.0 cm

74.316 [cm]

67.0 [cm]

74.316 [cm]74.316 [cm]

67.0 [cm]

74.3 cm

67.0 cm

64 & 128 MHz64 & 128 MHzNormal & first level controlled modesNormal & first level controlled modes


SAR (W/Kg)SAR (W/Kg) ΔΔT (T (ooC)C)

Month 1

Month 9


Results 64 MHz -- Normal mode


Results 64 MHz -- First level controlled mode


Results summary for fetus tissue only

• 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.

Fetus 64 MHz 128 MHz

Normal Mode

First level controlled mode

Normal Mode

First level controlled mode

Month 1-4 SAR limit Not

exceeded Exceeded Not exceeded Not exceeded

Temperature limit

Not exceeded Exceeded Not

exceeded Not exceeded

Month 5-9 SAR limit Not

exceeded Exceeded Not exceeded Not exceeded

Temperature limit

Not exceeded Exceeded Not

exceeded Not exceeded


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


MR critical semi active implant

• Braingates Ischemic Stroke System


MR critical medical devicesDefinition:• 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


MR critical medical devices

• Electrode Arrays Cap


MR critical medical devices

• AutoLITT Probe from Monteris

RF Head Coil (Clear)

Probe Driver Commander

Interface Platform

Probe

Head Fixation Device

Probe Driver Follower

PPI


Factors influencing implant and medical device heatingresponsible 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)


SAR distribution in different anatomical models at 1.5T


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


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.


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.


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


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


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.


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 calorimetrywas 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.


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.


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


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)


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


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


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, …


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


Thank you for your brain work ...

the future of mri safety w kainz 13 jul2009

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