Temperature Rise due to Medical Implants Niels Kuster Earl Zastrow Thursday, May 28, 15
Temperature Rise due to Medical ImplantsNiels KusterEarl Zastrow
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
RF Coupling Mechanisms w/ External Fields
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
RF Coupling Mechanisms w/ External Fields
in silico in vivo
From J. M. Henderson, et al., "Permanent Neurological Deficit Related to Magnetic Resonance Imaging in a Patient with Implanted Deep Brain Stimulation Electrodes for Parkinson's Disease: Case Report", Neurosurg., 57(5), 2005
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
RF Coupling Mechanisms: Simple Wires
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
RF Coupling Mechanisms: Simple Wire in Tissues
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
RF Coupling Mechanisms: Simple Wire in Tissues
ξ=0 rad/mξ=4 rad/mξ=9 rad/mξ=15 rad/m
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Content• IT’IS activities on implant safety• hypotheses• exposure limits & FDA safety considerations• localized heating due to generic implants• demonstration of MRI-safe implants• temperature rise during MRI exposure & risk management• conclusions
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
IT’IS Activities: Virtual Population (ViP)
ELLA female adult 1.60m, 58kg
FATSobese male 1.78m, 120kg
THELONIOUSboy 6y1.17m, 20kg
EARTHAgirl 8y1.35m, 30kg
ROBERTAgirl 5y1.09m, 16kgDUKE
male adult 1.74m, 70kg
BILLIEgirl 11y1.46m, 36kg
LOUISboy 14y1.65m, 50kg
DIZZYboy 8y 1.40m, 26kg
GLENN male elderly1.73m, 65kg
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
IT’IS Activities: Multi-Physics Solvers
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
IT’IS Activities: Testing Systems
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
IT’IS Activities: V&V
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Hypotheses• a significant portion of the population (people w/ passive or active medical
implants) is not protected from serious health hazards below 100 MHz (e.g., MRI, wireless power transfer)
• spatial averaging mass of 10g is too large for localized exposure• risk-benefit considerations needed for implants in MRI
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Exposure Safety Limits• temperature Limits
- FDA: no special consideration needed for <+2ºC temperature increase- ICNIRP: <+1ºC whole-body temperature increase- MRI: <39ºC/40ºC (normal/first level)
• EM/SAR Limits- ICNIRP Basic Restrictions: wbSAR 0.08/0.4 W/kg; psSAR10g: 2/10 W/kg - ICNIRP Derived Limits: E(S) & H(S) as function of frequency- IEC60601-2-33 (MRI): wbSAR: 2/4 W/kg; psSAR10g: not defined for body coil- ISO/TS10974 (Implant-MRI): follows IEC60601-2-33
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
ICNIRP Derived Limits (>100 kHz)
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Study• local deposition & ΔT in vicinity of implant
- 100 - 800 mm- 10MHz - 1GHz
• evaluation at ICNIRP limits• averaging mass for local absorption
‣ a significant portion of the population (people w/ passive or active medical implants) is not protected from serious health hazards below 100 MHz (e.g., MRI, wireless power transfer)
‣ spatial averaging mass of 10g is too large for localized exposure
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant StudypsSAR0.1g / ΔT = 55.5 W/kg / 1K
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Study
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Study
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Studyoccupational limituncontrolled limitderived limit for implant from study
occupational limituncontrolled limitderived limit for implant from study
occupational limituncontrolled limitderived limit for implant from study
occupational limituncontrolled limitderived limit for implant from study
Wire Length: 100mm Wire Length: 200mm
Wire Length: 500mm Wire Length: 800mm
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Studymass (g):20.3. Power (%):99.0
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):10.0. Power (%):96.0
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):1.0. Power (%):78.6
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):0.1. Power (%):39.4
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Studymass (g):10.0. Power (%):96.0
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):1.0. Power (%):78.6
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):0.1. Power (%):39.4
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
mass (g):20.3. Power (%):99.0
(mm)
(mm
)
-30 -20 -10 0 10 20 30
-10
0
10
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Study
0.01g0.1g1g10g
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Generic Implant Study
0.1$
1$
10$
100$
0.000001$ 0.00001$ 0.0001$ 0.001$ 0.01$ 0.1$ 1$
ΔT"[K
]"
Exposure"Radius"[m]"
Muscle$
Fat$
1g1mg 10g
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Conclusions: Safety of People w/ Implants• the hypothesis that “a significant portion of the population (people w/ passive or
active medical implants) is not protected from serious health hazards below 100 MHz (e.g., MRI, wireless power transfer)” is true
‣ revision of limits or statement in standard “people w/ implant are not protected” needed
• the hypothesis that “spatial averaging mass of 10g is too large for localized exposure” is true for implant safety consideration
‣ reduced averaging mass needed for conservative ΔT estimation
‣ restriction to contiguous tissue is important
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Demonstration of MRI Safety of Patients w/ Implants
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Evaluation of Implant in MRI: Concept• severity of RF-heating hazard: DBS, CI, pacemaker, SCS, etc.• magnitude of RF-heating relates to in vivo incident conditions
- MRI system: f(RF coil, power calculation & reporting)- implant: f(built,routing)- patient imaging condition: f(anatomy, posture, position)‣ in vivo incident conditions cannot be experimentally evaluated‣ need in silico approach to handle a multitude of variables
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Implant Safety during MRI: RF-Heating Hazard• IEC 60601-2-33: RF exposure limits‣ whole-body, head, partial-body SAR
• ISO/TS 10974: hazard evaluation‣ tissue deposition @ RF exposure limits
(60601-2-33)‣ tissue deposition --> hazard/risk
induced current and magnetic fields
induced electric fields
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Implant Safety during MRI: RF-Heating Hazard
BILLIE THELONIOUSELLADUKE
head imaging
thorax imaging
pelvis imaging
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Implant Safety during MRI: RF-Heating Hazard
BILLIE THELONIOUSELLADUKE
head imaging
thorax imaging
pelvis imaging
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Implant Safety during MRI: RF-Heating Hazard
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Implant in vivo Incident Conditions during MRI
Head Thoracic
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
ΔT during MRI
DBS (R) DBS (L) Pacemaker (R)
Pacemaker (L)
ps SAR0.1g (W/kg) 8.97E+03 8.71E+03 9.77E+01 5.26E+02
ΔT w/ implant (K) 92.5 96.4 1.3 6.3
ΔT w/o implant (K) <1 <1 <1 <1
ps SAR0.1g (W/kg) 1.11E+03 1.26E+03 1.01E+03 1.82E+03
ΔT w/ implant (K) 11.0 22.7 7.9 11.0
ΔT w/o implant (K) <1 <1 <1 <1
head
thor
acic
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Risk-Benefit Consideration for Implants• <+2ºC temperature limit
- would require new lead designs• pacing threshold limit (pacemaker): not yet standardized
- determined in animal studies- ΔT estimate of +10ºC- additional scar tissue around electrode considered to be acceptable
• RF-heating of brain tissue (DBS)- potentially very acute at current exposure limit- ΔT estimate of +100ºC from a generic implant
‣ the hypothesis “risk-benefit considerations for implants in MRI needed” is true
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Summary• the hypothesis that “a significant portion of the population (people w/ passive or
active medical implants) is not protected from serious health hazards below 100 MHz (e.g., MRI, wireless power transfer)” is true.
‣ revision of limits or statement in standard “people w/ implant are not protected” needed
• the hypothesis that “spatial averaging mass of 10g is too large for localized exposure” is true for implant safety consideration.
‣ reduced averaging mass needed for conservative ΔT estimation
‣ restriction to contiguous tissue is important• most elongated implants in MR are not intrinsically safe
‣ risk-benefit considerations for implants in MRI are needed
Thursday, May 28, 15
Temperature Rise due to Medical Implants ICNIRP Thermal Workshop, Istanbul Turkey, May 26-28, 2015
Acknowledgments• CO-ME, Swiss National Foundation• KTI, Commission of Innovations & Technology• Boston Scientific Corporation
Thursday, May 28, 15