Testing Services for Magnetic Resonance Imaging Therapy Testing Methods Stards for Magnetic Resonance (MR) Safety Compatibility of Medical Devices - Update G. Schaefers MR:comp GmbH MR Testing Laboratory Buschgrundstr. 33 45984 Gelsenkirchen Germany
Introduction Important product groups interacting with MR vascular implants stents, filters, clips, valves interventional instruments catheters, guidewires, endoscopes, orthopedic implants prostheses, fixation devices active implants medical electrical devices robots, monitoring equipment, injectors surgical instruments prostheses, fixation devices Innomotion, MR robot, Innomedic, Germany
The MR environment Controlled area 0.5 mt line MR cabin or Magnet room MR system MR-imaging volume MR system e.g. technical room
Subjects Methods Why is MR testing required for medical devices? Magnetic induced forces torques, which affect medical devices in in the the static magnetic field field are are dangerous for for patients, users equipment α F m magnet bore B 0 F g θ T m ref.: ferromagnetic device magnetic force F m, force due to gravity F g, static magnetic field strength B 0, magnetic torque T m (here: in the fringe field), defection angle α, rotation angle θ ASTM F2052-06, Stard Test Method for Measurement of Magnetically Induced Displacement Force on Medical Devices in the Magnetic Resonance Environment. 2006, www.astm.org Image extracted with permissen of from Taylor & Francis: G. Schaefers et al., Testing methods for MR safety compatibility of medical devices, Minimally Invasive Therapy. 2006; 15:2; 71 75
Why is MR testing required for medical devices? RF heating caused by by induced voltages currents at at current nodes is is dangerous for for patients users of of MR MR techniques i ~ E ~ conductive wire i ~ B 1~ B 1~ high temperature rises, if L wire c / (2 f ε tissue ); ε tissue 81 1,2 patient/ table (ground) B 1~ Heating caused caused by by conductive loops loops 1 1 ref.: 1 modified to A. Oppelt et al., from presentation 2 M. Konings et al., Heating Around Intravascular Guidewires by Resonating RF Waves. J. Magn. Reson. Imaging 2000;12:79 85 3 Yeung et al. RF Heating Due to Conductive Wires During MRI Depends on the Phase Distribution of the Transmit Field. Magn. Reson. Med. 48:1096-1098 (2002) at 0.2 T: λ/2 tissue 1.96 m at 1.5 T: λ/2 tissue 0.26 m at 3.0 T: λ/2 tissue 0.13 m Heating Heating caused caused by by conductive conductive wires wires similar similar structures structures (dipole (dipole antenna). antenna). Temperature Temperature may may rise rise also, also, if ifl wire is wire is < or or > λ/2 1,3 λ/2 tissue 1,3 tissue
RF heating aspects of of leads by by courtesy courtesy of of J. J. Helfer Helfer et et al., al., Biophan Biophan Inc., Inc., USA USA Ambient = 25 C 45 C Max Ambient = 25 C 75 C Max 30 C Surface 30 C Surface Isothermal plot in phantom (Passive fixation lead) Close-up of isotherms (Cross-section of active fixation lead) ref.: www.biophan.com Temperature profile from mathematical modeling of active fixation pacemaker lead in an MRI field. The thermal conductivity of the lead transports substantial heat creating a physically separated region of peak temperature
Why is MR testing required for medical devices? Switched gradient magnetic fields contribute negligible to to induced heating, but but dynamic gradient magnetic fields can can cause nerve stimulation can can lead lead to to induced currents in in conductive structures Factor of approx. 100 to 1000 between RF frequency (MHz) gradient frequency (khz) G z G z + G = e.g. 60 mt/m 90 mv SL = 150 mt/m/ms G = 15 mt/m t s = stimulation t s, eff. = e.g. 0.2 ms G z - Slew rate (SL) = e.g. 300 mt/m/ms t Induced voltages in a bipolar pacemaker electrode, Selute Picotip 4034, Guidant, Giessen, Germany ref. plot: Xixi Zhang, basic studies project, University of Applied Sciences Fachhochschule Gelsenkirchen MR:comp GmbH, Gelsenkrichen, Germany t s, = 0.1 ms db/dt is dependent on gradient magnetic field vector position (x,y,z) within the gradient coil
Why is MR testing required for medical devices? Computer Computersimulation simulation Assistance Assistancefor formr MRsafety safetytesting testing EE- H-field H-fieldof ofan anmr MRactive activeimplant implant(resonant (resonantcircuit) circuit)at at42,6 42,6MHz MHz ref.: ref.: Numerical NumericalInvestigation InvestigationofofElectromagnetic ElectromagneticProperties PropertiesofofMR MRActive ActiveImplants, Implants,S.S.Schwarzer, Schwarzer,U. U.Jorczyk, Jorczyk, A.A.Melzer, W. Zylka, University of Applied Sciences FH Gelsenkirchen, Germany, DGBMT 2004 Melzer, W. Zylka, University of Applied Sciences FH Gelsenkirchen, Germany, DGBMT 2004
-- Evaluation of of MR MR characteristics of of medical devices -- H- H- E-field E-field components, resonant frequencies of of electrical conductive structures MR MR active active devices with with resonant circuits circuits -- SAR SAR temperature distribution, worst-case estimation E-field SAR Temperature red color due to material differentiation styrolene material insert as crotch contact between upper thighs Qualitative results of numerical investigation of hip prostheses in a human torso phantom in MRI, red = high values, blue = low values J. Stenschke, Master-Thesis,
Why is MR testing required for medical devices? Safe functioning of of the external device used with with MR. MR. Any Any interferences caused by by the the MR MR environment on on -- active/ non-active device systems? (inhibition of ofelec. circuits/ mechanical components (levers, etc.)) -- RF RF sensitive devices? (Electromagnetic compatibility) -- high high acoustic noise level level of of the the MR MR system? (interferences with with sensors, systems, etc.) etc.) of of the MR system (patient safety, image quality) Any Any interferences caused by by the the external device? -- RF RF emitting devices (Electromagnetic compatibility) between different external medical devices (implant, instrument, etc.) etc.) within the the MR MR environment
Why is MR testing required for medical devices? RF interferences (stripes dots) -- RF RF emitting devices (Electromagnetic compatibility) phase direction stripes dots are caused by periodic emitted signals inside the RF cabin dots caused by synchonous signals stripes caused by unsynchronous signals freqeuncy direction from: Arnulf Oppelt (ed.): Imaging Systems for Medical Diagnostics. Publicis Corporate Publishing, Erlangen 2005
Why is MR testing required for medical devices? RF interferences (stripes dots) -- RF RF emitting devices (Electromagnetic compatibility) possible reasons 4 : freqeuncy direction unshielded cables electronic devices, e.g. monitoring systems switched power supplies computer clocks 4 Arnulf Oppelt (ed.): Imaging Systems for Medical Diagnostics. Publicis Corporate Publishing, Erlangen 2005 phase direction Image by courtesy of Dr. H. Kugel, Department of Clinical Radiology, University of Muenster, Muenster, Germany
Why is MR testing required for medical devices? MR Imaging artifacts influences to to the the magnetic field field cause image distortion Susceptibility artifacts are are dependent on on several parameters, for for example 5 5 Strength of of B 0 0 Orientation to to B 0 0 Susceptibility of of device s material Direction of of phase encoding Technique of of sequence (SE/ (SE/ GRE) Time of of echo 6 Susceptibility artifact Vena Cava Filter in MRI, Anthéor,Boston Scientific 1.5 T, flash2d, TR 300 ms, TE 6 ms, FA 40, FoV 180mm/ 256 5 L. W. Bartels et al., Improved lumen visualization in metallic vascular implants by reducing RF artifacts. Magn Reson Med. 2002 Jan;47(1):171-80 6 Image extracted with permission of from Taylor & Francis: G. Schaefers et al., Testing methods for MR safety compatibility of medical devices, Minimally Invasive Therapy. 2006; 15:2; 71 75
Why is MR testing required for medical devices? MR Imaging artifacts influences to to the the magnetic field field cause image distortion Susceptibility artifacts are are dependent on on several parameters, for for example 4 4 Strength of of B 0 0 Orientation to to B 0 0 Susceptibility of of device s material Direction of of phase encoding Technique of of sequence (SE/ (SE/ GRE) Time of of echo Susceptibility artifact SMD capacitors within MR environment 1.0 Tesla, Philips Medical System Sequence: gradient echo FFE, TR 22 ms, TE 6 ms, FA 40 4 L. W. Bartels et al., Improved lumen visualization in metallic vascular implants by reducing RF artifacts. Magn Reson Med. 2002 Jan;47(1):171-80
Why is MR testing required for medical devices? MR Imaging artifacts influences to to the the magnetic field field cause image distortion Susceptibility artifacts are are dependent on on several parameters, for for example 5 5 Strength of of B 0 0 Orientation to to B 0 0 Susceptibility of of device s material Direction of of phase encoding Technique of of sequence (SE/ (SE/ GRE) Time of of echo 5 L. W. Bartels et al., Improved lumen visualization in metallic vascular implants by reducing RF artifacts. Magn Reson Med. 2002 Jan;47(1):171-80 10 cm Susceptibility artifacts 1.5 Tesla, flash 2D, TE = 2.83 ms, TR = 124 ms Holding arm ( 40 mm) for e.g. instruments, by courtesy of Dr. M. Vogele, Medical Intelligence, Schwabmunich, Germany
Why is MR testing required for medical devices? MR Imaging artifacts Electromagnetic shielding of of RF RF signals is is causing void voidof of MR MR information RF RF artifacts are are dependent on on several parameters, for for example 4 4 Strength of of B 0 0 Orientation to to MR MR coils coils Conductivity of of device s material Design geometry of of the the device Flip Flip angle, strength of of B 1 1 4 L. W. Bartels et al., Improved lumen visualization in metallic vascular implants by reducing RF artifacts. Magn Reson Med. 2002 Jan;47(1):171-80 RF artifact within the filter lumen Vena Cava Filter in MRI, TrapEase, Cordis 1.5 T, flash2d, TR 300 ms, TE 6 ms, FA 40,, FoV 180mm/ 256 Image extracted with permission of from Taylor & Francis: G. Schaefers et al., Min. Inva. Therapy. 2006; 15:2; 71 75 Artifacts lead lead to to difficulty with with follow-up examination of of patients with with already implanted devices or or if if using unsuitable instruments/devices
Results Testing issues for medical devices used with MR Magnetic induced displacement force Magnetic induced torque Radio frequency (RF) (RF) induced heating Gradient RF RF induced voltages Safe Safe functioning of of the the external device within the the MR MR environment Safe Safe operation of of the the MR MR system MR MR image artifacts quality issues Susceptibility artifacts (dependent on on material) RF RF artifacts of of implants devices in in the the imaging volume (signal shielding amplification effects) RF RF artifacts in in the the MR MR image due due to to RF RF emission Signal-to-Noise ratio ratio (SNR) B 0 -Field 0 homogeneity (image uniformity/ spatial distortion) list list is is not not limited limited to to above above mentioned mentioned issues issues
Current situation of medical devices in conjunction with MRI MR system manufacturers Patient with implants have a contraindication for MRI Notified authorities e.g. EU notified bodies, US FDA concerned about patient safety recommend MR testing for labeling of devices further research necessary INPUT MR testing of medical devices according to international stards Patients with implants could have clinical indication for MR examination Implant manufacturers require guidance for developing MR safe/conditional devices Clinicians/ MR users want to use advantages of MRI for patient diagnosis get help by MR testing results
The historically definition* of MR safety compatibility MR MR safe safe --The The device, when used in in the the MR MR environment, has has been demonstrated to to present no no additional risk risk to to the the patient or or other individuals, but but may may affect the the quality of of the the diagnostic information. MR MR compatible --The The device, when used in in the the MR MR environment, is is MR MR safe safe has has been demonstrated to to neither significantly affect the the quality of of the the diagnostic information nor nor have its its operations affected by by the the MR MR device. Report MR MR test test conditions MR MR safe safe for for one one set set of of condition Consider more extreme MR MR conditions Definitions Definitions icons icons extracted, extracted, with with permission, permission, from from ASTM ASTM F2503-05, F2503-05, Stard Stard Practice Practice for for Marking Marking Medical Medical Devices Devices Other Other Items Items for for Safety Safety in in the the MR MR Environment, Environment, copyright copyright ASTM ASTM International, International, 100 100 Barr Barr Harbor Harbor Drive, Drive, West West Conshohocken, Conshohocken, PA PA 19428. 19428. A A copy copy of of the the complete complete stard stard may may be be purchased purchased from from service@astm.org, service@astm.org, website: website: www.astm.org. www.astm.org.
The active definitions of MR safety: MR Safe MR MR Safe an item item that that poses no no known hazards in in all all MR MR environments. or or (in (in addition, addition, icons icons have have a a black black white white option) option) Definitions Definitions icons icons extracted, extracted, with with permission, permission, from from ASTM ASTM F2503-05, F2503-05, Stard Stard Practice Practice for for Marking Marking Medical Medical Devices Devices Other Other Items Items for for Safety Safety in in the the MR MR Environment, Environment, copyright copyright ASTM ASTM International, International, 100 100 Barr Barr Harbor Harbor Drive, Drive, West West Conshohocken, Conshohocken, PA PA 19428. 19428. A A copy copy of of the the complete complete stard stard may may be be purchased purchased from from service@astm.org, service@astm.org, website: website: www.astm.org. www.astm.org.
The active definitions of MR safety: MR Conditional MR MR Conditional an item item that that has has been demonstrated to to pose no no known hazards in in a specified MR MR environment with with specified conditions of of use. use. Field conditions that that define the the specified MR MR environment include field field strength, spatial gradient, db/dt (time rate rate of of change of of the the magnetic field), radio frequency (RF) (RF) fields, specific absorption rate rate (SAR). Additional conditions, including specific configurations of of the the item, may may be be required. (in (in addition, addition, icon icon has has a a black black white white option) option) Definitions Definitions icons icons extracted, extracted, with with permission, permission, from from ASTM ASTM F2503-05, F2503-05, Stard Stard Practice Practice for for Marking Marking Medical Medical Devices Devices Other Other Items Items for for Safety Safety in in the the MR MR Environment, Environment, copyright copyright ASTM ASTM International, International, 100 100 Barr Barr Harbor Harbor Drive, Drive, West West Conshohocken, Conshohocken, PA PA 19428. 19428. A A copy copy of of the the complete complete stard stard may may be be purchased purchased from from service@astm.org, service@astm.org, website: website: www.astm.org. www.astm.org.
The active definitions of MR safety: MR Unsafe MR MR Unsafe an item item that that is is known to to pose hazards in in all all MR MR environments. (in (in addition, addition, icon icon has has a a black black white white option) option) Definitions Definitions icons icons extracted, extracted, with with permission, permission, from from ASTM ASTM F2503-05, F2503-05, Stard Stard Practice Practice for for Marking Marking Medical Medical Devices Devices Other Other Items Items for for Safety Safety in in the the MR MR Environment, Environment, copyright copyright ASTM ASTM International, International, 100 100 Barr Barr Harbor Harbor Drive, Drive, West West Conshohocken, Conshohocken, PA PA 19428. 19428. A A copy copy of of the the complete complete stard stard may may be be purchased purchased from from service@astm.org, service@astm.org, website: website: www.astm.org. www.astm.org.
MR compatibility - MR Image Artifacts An An MR MR image artifact is is not not considered as as a direct safety issue by by ASTM F2503-05 Stard Practice for for Marking Medical Devices therefore hled as as separate issue, but but artifact information provide important help help for for the the physician before MR MR scanning of of a patient with with implant or or other item item a statement about MR MR image artifacts produced by by an an implant/ item item should be be included in in the the product labeling/ patient implant card card
Radiopacity of medical devices Evaluation of of the the transparency of of materials to to X-rays X-rays Required to to stay stay compatible with with the the commonly used used X-ray X-ray imaging techniques Materials with with low low artifact artifact behavior can can have have a minor minor X-ray X-ray attenuation X-ray X-ray suitable materials can can produce MR MR image image artifacts MR Unsafe MR Conditional MR Safe radiopaque low MR image artifact behavior (formerly MR compatible ) MR safety, MR image artifacts radiopacity should be considered as interconnected system
Current stards for MR safety compatibility testing IEC IEC 60601-2-33 60601-2-33 Medical Medical electrical electrical equipment equipment --Particular Particular requirements requirements for for the the safety safety of of magnetic magnetic resonance resonance equipment equipment for for medical medical diagnosis diagnosis ASTM ASTM NEW NEW F2503 F2503 --Stard Stard Practice Practice for for Marking Marking Medical Medical Devices Devices Other Other Items Items for for Safety Safety in in the the Magnetic Magnetic Resonance Resonance Environment Environment Stard Stard Test Test Method Method for for Measurement Measurement F2052 F2052 --of of Magnetically Magnetically Induced Induced Displacement Displacement Force Forceon on Medical Medical Devices Devices in in MR-environment MR-environment F2213 F2213 --of of Magnetically Magnetically Induced Induced Torque Torqueon on Medical Medical Devices Devices in in the the MRE MRE F2182 F2182 --of of Radio Radio Frequency Frequency Induced Induced Heating HeatingNear Passive Passive Implants Implants During DuringMRI MRI F2119 F2119 --for for Evaluation Evaluation of of MR MR Image Image Artifacts Artifactsfrom from Passive Passive Implants Implants Detailed Detailed Information Information for for testing testing is is provided provided in in above above stards stards FDA FDA recommends recommends ASTM ASTM test test methods methods for for device device approval approval
Stards considering MR testing for medical devices ISO ISO 14630:2005 Non-active surgical implants -- --General requirements ISO ISO 9713:2002 Neurosurgical implants -- --Self-closing intracranial aneurysm clips clips ISO ISO 7197:1997 Neurosurgical implants -- --Sterile, single-use hydrocephalus shunts shunts components ISO ISO 5840:2005 Cardiovascular implants -- --Cardiac valve valve prostheses ISO ISO 25539-1:2003 Cardiovascular implants -- --Endovascular devices -- --Part 1: 1: Endovascular prostheses Part Part 2: 2: Vascular stents stentsunder development development EN EN 14299 14299 --Non Non active active surgical implants. Particular requirements for for cardiac cardiac vascular implants. Specific requirements for for arterial arterial stents. stents. MR MR testing testing is is required for for heating, movements evaluation of of image image artifacts for for product labeling requirements against interferences from external electrical magnetic fields EN EN 45502-1:1998 Active Active implantable medical devices. General requirements EN EN 45502-2-1:2003 Active Active implantable medical devices. Particular requirements (cardiac pace pace makers)
FDA guidelines for Industry Staff considering MR testing for medical devices Non-Clinical Tests Tests Recommended Labeling for for Intravascular Stents Stents Associated Delivery Systems, 2005 2005 Implantable Radiofrequency Transponder System for for Patient Patient Identification Health Health Information, 2004 2004 Implantable Middle Middle Ear Ear Hearing Device, 2003 2003 Cardiovascular Intravascular Filter Filter 510(k) 510(k) Submissions, 1999 1999 Medical Devices with with Sharps Sharps Injury Injury Prevention Features, 2005 2005 Intravascular Administration Sets Sets Premarket Notification Submissions [510(k)], 2005 2005 Guidelines contain contain MR MR safety safety recommendations in in general up up to to detailed information links links to to ASTM ASTM test test methods Obsolete: A Primer Primer on on Medical Device Device Interactions with with Magnetic Resonance Imaging Systems, 1997 1997 contains appendix with with questions of of MR MR safety safety issues issues regarding risk risk analysis
MRI statement for device approval The The FDA FDA asks asks for for MR MR safety compatibility testing of of devices Examples for MRI statements from recent device approvals
ref.:from publicized FDA approvals on the Internet
Conclusion Magnetic resonance in in medicine is is an an dynamic innovative field with an an increasing number of of cases associated products Implants, instruments other medical devices interact with MR techniques thus creating safety risks incompatibility International MR testing safety stards are required for for minimizing risks guide manufacturing of of MR safe compatible products
Goals of MR stards for medical devices Increase of of safety for for patient user of of MR techniques, as as well as as for for MR equipment additionally used devices Meet the needs of of manufacturers of of MR safe compatible devices for for providing optimal patient careincreasing diagnostic accuracies in in future. Enable the use of of the advantages of of MR technology to to patients with implants the application of of additionally devices
Testing Services for Magnetic Resonance Imaging Therapy Thank you very much for Your attention! MR:comp GmbH MR Safety Testing Laboratory Buschgrundstrasse 33 45894 Gelsenkirchen Germany Phone +49 209 604 893 82 Fax +49 209 604 893 88 Email info@mrcomp.com