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Petzold J, Schmitter S, Silemek B, Winter L, Speck O, Ittermann B, Seifert F. Towards an integrated radiofrequency safety concept for implant carriers in MRI based on sensor-equipped implants and parallel transmission. NMR IN BIOMEDICINE 2023; 36:e4900. [PMID: 36624556 DOI: 10.1002/nbm.4900] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 10/11/2022] [Accepted: 01/04/2023] [Indexed: 06/15/2023]
Abstract
To protect implant carriers in MRI from excessive radiofrequency (RF) heating it has previously been suggested to assess that hazard via sensors on the implant. Other work recommended parallel transmission (pTx) to actively mitigate implant-related heating. Here, both ideas are integrated into one comprehensive safety concept where native pTx safety (without implant) is ensured by state-of-the-art field simulations and the implant-specific hazard is quantified in situ using physical sensors. The concept is demonstrated by electromagnetic simulations performed on a human voxel model with a simplified spinal-cord implant in an eight-channel pTx body coil at 3 T . To integrate implant and native safety, the sensor signal must be calibrated in terms of an established safety metric (e.g., specific absorption rate [SAR]). Virtual experiments show that E -field and implant-current sensors are well suited for this purpose, while temperature sensors require some caution, and B 1 probes are inadequate. Based on an implant sensor matrix Q s , constructed in situ from sensor readings, and precomputed native SAR limits, a vector space of safe RF excitations is determined where both global (native) and local (implant-related) safety requirements are satisfied. Within this safe-excitation subspace, the solution with the best image quality in terms of B 1 + magnitude and homogeneity is then found by a straightforward optimization algorithm. In the investigated example, the optimized pTx shim provides a 3-fold higher mean B 1 + magnitude compared with circularly polarized excitation for a maximum implant-related temperature increase ∆ T imp ≤ 1 K . To date, sensor-equipped implants interfaced to a pTx scanner exist as demonstrator items in research labs, but commercial devices are not yet within sight. This paper aims to demonstrate the significant benefits of such an approach and how this could impact implant-related RF safety in MRI. Today, the responsibility for safe implant scanning lies with the implant manufacturer and the MRI operator; within the sensor concept, the MRI manufacturer would assume much of the operator's current responsibility.
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Affiliation(s)
- Johannes Petzold
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Berk Silemek
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Lukas Winter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Oliver Speck
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Bernd Ittermann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
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Bottauscio O, Arduino A, Chiampi M, Zilberti L. Simplified modeling of implanted medical devices with metallic filamentary closed loops exposed to low or medium frequency magnetic fields. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2023; 229:107316. [PMID: 36566651 DOI: 10.1016/j.cmpb.2022.107316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2022] [Revised: 12/12/2022] [Accepted: 12/16/2022] [Indexed: 06/17/2023]
Abstract
BACKGROUND AND OBJECTIVES Electric currents are induced in implanted medical devices with metallic filamentary closed loops (e.g., fixation grids, stents) when exposed to time varying magnetic fields, as those generated during certain diagnostic and therapeutic biomedical treatments. A simplified methodology to efficiently compute these currents, to estimate the altered electromagnetic field distribution in the biological tissues and to assess the consequent biological effects is proposed for low or medium frequency fields. METHODS The proposed methodology is based on decoupling the handling of the filamentary wire and the anatomical body. To do this, a circuital solution is adopted to study the metallic filamentary implant and this solution is inserted in the electromagnetic field solution involving the biological tissues. The Joule losses computed in the implant are then used as a forcing term for the thermal problem defined by the bioheat Pennes' equation. The methodology is validated against a model problem, where a reference solution is available. RESULTS The proposed simplified methodology is proved to be in good agreement with solutions provided by alternative approaches. In particular, errors in the amplitude of the currents induced in the wires result to be always lower than 3%. After the validation, the methodology is applied to check the interactions between the magnetic field generated by different biomedical devices and a skull grid, which represents a complex filamentary wire implant. CONCLUSIONS The proposed simplified methodology, suitable to be applied to closed loop wires in the low to intermediate frequency range, is found to be sufficiently accurate and easy to apply in realistic exposure scenarios. This modeling tool allows analyzing different types of small implants, from coronary and biliary duct stents to orthopedic grids, under a variety of exposure scenarios.
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Affiliation(s)
- Oriano Bottauscio
- Istituto Nazionale di Ricerca Metrologica (INRiM), Strada Delle Cacce 91, 10135 Torino, Italy.
| | - Alessandro Arduino
- Istituto Nazionale di Ricerca Metrologica (INRiM), Strada Delle Cacce 91, 10135 Torino, Italy
| | - Mario Chiampi
- Istituto Nazionale di Ricerca Metrologica (INRiM), Strada Delle Cacce 91, 10135 Torino, Italy
| | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica (INRiM), Strada Delle Cacce 91, 10135 Torino, Italy
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Sadeghi-Tarakameh A, Zulkarnain NIH, He X, Atalar E, Harel N, Eryaman Y. A workflow for predicting temperature increase at the electrical contacts of deep brain stimulation electrodes undergoing MRI. Magn Reson Med 2022; 88:2311-2325. [PMID: 35781696 PMCID: PMC9545305 DOI: 10.1002/mrm.29375] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 06/08/2022] [Accepted: 06/09/2022] [Indexed: 11/13/2022]
Abstract
Purpose The purpose of this study is to present a workflow for predicting the radiofrequency (RF) heating around the contacts of a deep brain stimulation (DBS) lead during an MRI scan. Methods The induced RF current on the DBS lead accumulates electric charge on the metallic contacts, which may cause a high local specific absorption rate (SAR), and therefore, heating. The accumulated charge was modeled by imposing a voltage boundary condition on the contacts in a quasi‐static electromagnetic (EM) simulation allowing thermal simulations to be performed with the resulting SAR distributions. Estimating SAR and temperature increases from a lead in vivo through EM simulation is not practical given anatomic differences and variations in lead geometry. To overcome this limitation, a new parameter, transimpedance, was defined to characterize a given lead. By combining the transimpedance, which can be measured in a single calibration scan, along with MR‐based current measurements of the lead in a unique orientation and anatomy, local heating can be estimated. Heating determined with this approach was compared with results from heating studies of a commercial DBS electrode in a gel phantom with different lead configurations to validate the proposed method. Results Using data from a single calibration experiment, the transimpedance of a commercial DBS electrode (directional lead, Infinity DBS system, Abbott Laboratories, Chicago, IL) was determined to be 88 Ω. Heating predictions using the DBS transimpedance and rapidly acquired MR‐based current measurements in 26 different lead configurations resulted in a <23% (on average 11.3%) normalized root‐mean‐square error compared to experimental heating measurements during RF scans. Conclusion In this study, a workflow consisting of an MR‐based current measurement on the DBS lead and simple quasi‐static EM/thermal simulations to predict the temperature increase around a DBS electrode undergoing an MRI scan is proposed and validated using a commercial DBS electrode. Click here for author‐reader discussions
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Affiliation(s)
| | | | - Xiaoxuan He
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Ergin Atalar
- Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey.,National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey
| | - Noam Harel
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
| | - Yigitcan Eryaman
- Center for Magnetic Resonance Research (CMRR), University of Minnesota, Minneapolis, Minnesota, USA
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Arduino A, Bottauscio O, Chiampi M, Zanovello U, Zilberti L. A contribution to MRI safety testing related to gradient-induced heating of medical devices. Magn Reson Med 2022; 88:930-944. [PMID: 35344605 PMCID: PMC9314691 DOI: 10.1002/mrm.29235] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2021] [Revised: 01/22/2022] [Accepted: 02/24/2022] [Indexed: 12/26/2022]
Abstract
PURPOSE To theoretically investigate the feasibility of a novel procedure for testing the MRI gradient-induced heating of medical devices and translating the results into clinical practice. METHODS The concept of index of stress is introduced by decoupling the time waveform characteristics of the gradient field signals from the field spatial distribution within an MRI scanner. This index is also extended to consider the anisotropy of complex bulky metallic implants. Merits and drawbacks of the proposed index of stress are investigated through virtual experiments. In particular, the values of the index of stress evaluated for realistic orthopedic implants placed within an ASTM phantom are compared with accurate heating simulations performed with 2 anatomic body models (a man and a woman) implanted through a virtual surgery procedure. RESULTS The manipulation of the proposed index of stress allows to identify regions within the MRI bore where the implant could affect the safety of the examinations. Furthermore, the conducted analysis shows that the power dissipated into the implant by the induced eddy currents is a dosimetric quantity that estimates well the maximum temperature increase in the tissues surrounding the implant. CONCLUSION The results support the adoption of an anisotropic index of stress to regulate the gradient-induced heating of geometrically complex implants. They also pave the way for a laboratory characterization of the implants based on electrical measurements, rather than on thermal measurements. The next step will be to set up a standardized experimental procedure to evaluate the index of stress associated with an implant.
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Affiliation(s)
| | | | - Mario Chiampi
- Istituto Nazionale di Ricerca Metrologica (INRIM), Torino, Italy
| | | | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica (INRIM), Torino, Italy
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5
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Silemek B, Seifert F, Petzold J, Hoffmann W, Pfeiffer H, Speck O, Rose G, Ittermann B, Winter L. Rapid safety assessment and mitigation of radiofrequency induced implant heating using small root mean square sensors and the sensor matrix Q s. Magn Reson Med 2021; 87:509-527. [PMID: 34397114 DOI: 10.1002/mrm.28968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 07/20/2021] [Accepted: 07/26/2021] [Indexed: 11/07/2022]
Abstract
PURPOSE Rapid detection and mitigation of radiofrequency (RF)-induced implant heating during MRI based on small and low-cost embedded sensors. THEORY AND METHODS A diode and a thermistor are embedded at the tip of an elongated mock implant. RF-induced voltages or temperature change measured by these root mean square (RMS) sensors are used to construct the sensor Q-Matrix (QS ). Hazard prediction, monitoring and parallel transmit (pTx)-based mitigation using these sensors is demonstrated in benchtop measurements at 300 MHz and within a 3T MRI. RESULTS QS acquisition and mitigation can be performed in <20 ms demonstrating real-time capability. The acquisitions can be performed using safe low powers (<3 W) due to the high reading precision of the diode (126 µV) and thermistor (26 µK). The orthogonal projection method used for pTx mitigation was able to reduce the induced signals and temperatures in all 155 investigated locations. Using the QS approach in a pTx capable 3T MRI with either a two-channel body coil or an eight-channel head coil, RF-induced heating was successfully assessed, monitored and mitigated while the image quality outside the implant region was preserved. CONCLUSION Small (<1.5 mm3 ) and low-cost (<1 €) RMS sensors embedded in an implant can provide all relevant information to predict, monitor and mitigate RF-induced heating in implants, while preserving image quality. The proposed pTx-based QS approach is independent of simulations or in vitro testing and therefore complements these existing safety assessments.
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Affiliation(s)
- Berk Silemek
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Johannes Petzold
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Werner Hoffmann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Harald Pfeiffer
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Oliver Speck
- Biomedical Magnetic Resonance, Otto-von-Guericke-University Magdeburg, Magdeburg, Germany.,German Center for Neurodegenerative Diseases (DZNE), Magdeburg, Germany.,Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany.,Center for Behavioral Brain Sciences (CBBS), Magdeburg, Germany
| | - Georg Rose
- Center for Behavioral Brain Sciences (CBBS), Magdeburg, Germany.,Institute for Medical Engineering and Research Campus STIMULATE, University of Magdeburg, Magdeburg, Germany
| | - Bernd Ittermann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Lukas Winter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
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Mattei E, Censi F, Calcagnini G, Lucano E, Angelone LM. A combined computational and experimental approach to assess the transfer function of real pacemaker leads for MR radiofrequency-induced heating. MAGMA (NEW YORK, N.Y.) 2021; 34:619-630. [PMID: 33555489 DOI: 10.1007/s10334-021-00909-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 12/25/2020] [Accepted: 01/15/2021] [Indexed: 06/12/2023]
Abstract
OBJECTIVE To propose and validate a variation of the classic techniques for the estimation of the transfer function (TF) of a real pacemaker (PM) lead. METHODS The TF of three commercially available PM leads was measured by combining data from experimental measurements and numerical simulations generated by three sources: a) the experimental local SAR at the tip of the PM lead (single measurement point) exposed to a 64 MHz birdcage body coil; b) the experimental current distribution along the PM lead, obtained by directly injecting a 64 MHz signal inside the lead; c) the electric field (E-field) simulated with a computational model of the 64 MHz birdcage body coil adopted in the experimental measurement performed in a). The effect of the lead trajectory on the estimation of the TF was also estimated. RESULTS The proposed methodology was validated by comparing the SAR obtained from the PM lead TF with experimental measurements: a maximum difference of 2.2 dB was observed. It was also shown that the estimation of the TF cannot be considered independent with the lead trajectory: a variation of the SAR estimation up to 3.4 dB was observed. CONCLUSION For the three PM lead tested, the error in the SAR estimation is within the uncertainty level of SAR measurements (± 2 dB). Additionally, the estimation of the TF using the reciprocity principle is influenced by the particular lead trajectory adopted, even if the consequent variability in the SAR estimation is still close to the uncertainty level of SAR measurements.
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Affiliation(s)
- Eugenio Mattei
- Department of Cardiovascular, Endocrine-Metabolic Diseases and Aging, National Institute of Health, Viale Regina Elena 299, 00161, Rome, Italy.
| | - F Censi
- Department of Cardiovascular, Endocrine-Metabolic Diseases and Aging, National Institute of Health, Viale Regina Elena 299, 00161, Rome, Italy
| | - G Calcagnini
- Department of Cardiovascular, Endocrine-Metabolic Diseases and Aging, National Institute of Health, Viale Regina Elena 299, 00161, Rome, Italy
| | - E Lucano
- Department of Information Engineering, Electronics and Telecommunications of the University of Rome "Sapienza", Rome, Italy
| | - L M Angelone
- Division of Biomedical Physics of the Food and Drug Administration, Washington, USA
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Stijnman PRS, Erturk MA, van den Berg CAT, Raaijmakers AJE. A single setup approach for the MRI-based measurement and validation of the transfer function of elongated medical implants. Magn Reson Med 2021; 86:2751-2765. [PMID: 34036617 PMCID: PMC8596675 DOI: 10.1002/mrm.28840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 04/23/2021] [Accepted: 04/23/2021] [Indexed: 12/15/2022]
Abstract
Purpose To propose a single setup using the MRI to both measure and validate the transfer function (TF) of linear implants. Conventionally, the TF of an implant is measured in one bench setup and validated using another. Methods It has been shown that the TF can be measured using MRI. To validate this measurement, the implant is exposed to different incident electric fields, while the temperature increase at the tip is monitored. For a good validation, the incident electric fields that the implant is exposed to should be orthogonal. We perform a simulation study on six different methods that change the incident electric field. Afterward, a TF measurement and validation study using the best method from the simulations is performed. This is done with fiberoptic temperature probes at 1.5 T for four linear implant structures using the proposed single setup. Results The simulation study showed that positioning local transmit coils at different locations along the lead trajectory has a similar validation quality compared with changing the implant trajectory (ie, the conventional validation method). For the validation study that was performed, an R2 ≥ 0.91 was found for the four investigated leads. Conclusion A single setup to both measure and validate the transfer function using local transmit coils has been shown to work. The benefits of using the proposed validation method are that there is only one setup required instead of two and the implant trajectory is not varied; therefore, the relative distance between the leap tip and the temperature probe is constant.
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Affiliation(s)
- Peter R S Stijnman
- Computational Imaging Group for MRI diagnostics and therapy, Center for Image Sciences UMC Utrecht, Utrecht, the Netherlands.,Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Brabant, the Netherlands
| | - M Arcan Erturk
- Restorative Therapies Group, Implantables R&D, Medtronic PLC, Minneapolis, Minnesota, USA
| | - Cornelis A T van den Berg
- Computational Imaging Group for MRI diagnostics and therapy, Center for Image Sciences UMC Utrecht, Utrecht, the Netherlands
| | - Alexander J E Raaijmakers
- Computational Imaging Group for MRI diagnostics and therapy, Center for Image Sciences UMC Utrecht, Utrecht, the Netherlands.,Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Brabant, the Netherlands
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Yildirim DK, Bruce C, Uzun D, Rogers T, O'Brien K, Ramasawmy R, Campbell-Washburn A, Herzka DA, Lederman RJ, Kocaturk O. A 20-gauge active needle design with thin-film printed circuitry for interventional MRI at 0.55T. Magn Reson Med 2021; 86:1786-1801. [PMID: 33860962 DOI: 10.1002/mrm.28804] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2020] [Revised: 03/05/2021] [Accepted: 03/23/2021] [Indexed: 01/14/2023]
Abstract
PURPOSE This work aims to fabricate RF antenna components on metallic needle surfaces using biocompatible polyester tubing and conductive ink to develop an active interventional MRI needle for clinical use at 0.55 Tesla. METHODS A custom computer numeric control-based conductive ink printing method was developed. Based on electromagnetic simulation results, thin-film RF antennas were printed with conductive ink and used to fabricate a medical grade, 20-gauge (0.87 mm outer diameter), 90-mm long active interventional MRI needle. The MRI visibility performance of the active needle prototype was tested in vitro in 1 gel phantom and in vivo in 1 swine. A nearly identical active needle constructed using a 44 American Wire Gauge insulated copper wire-wound RF receiver antenna was a comparator. The RF-induced heating risk was evaluated in a gel phantom per American Society for Testing and Materials (ASTM) 2182-19. RESULTS The active needle prototype with printed RF antenna was clearly visible both in vitro and in vivo under MRI. The maximum RF-induced temperature rise of prototypes with printed RF antenna and insulated copper wire antenna after a 3.96 W/kg, 15 min. long scan were 1.64°C and 8.21°C, respectively. The increase in needle diameter was 98 µm and 264 µm for prototypes with printed RF antenna and copper wire-wound antenna, respectively. CONCLUSION The active needle prototype with conductive ink printed antenna provides distinct device visibility under MRI. Variations on the needle surface are mitigated compared to use of a 44 American Wire Gauge copper wire. RF-induced heating tests support device RF safety under MRI. The proposed method enables fabrication of small diameter active interventional MRI devices having complex geometries, something previously difficult using conventional methods.
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Affiliation(s)
- Dursun Korel Yildirim
- Institute of Biomedical Engineering, Bogazici University, Kandilli Campus, Istanbul, Turkey.,Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Christopher Bruce
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Dogangun Uzun
- Institute of Biomedical Engineering, Bogazici University, Kandilli Campus, Istanbul, Turkey.,Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Toby Rogers
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Kendall O'Brien
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Rajiv Ramasawmy
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Adrienne Campbell-Washburn
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Daniel A Herzka
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Robert J Lederman
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Ozgur Kocaturk
- Institute of Biomedical Engineering, Bogazici University, Kandilli Campus, Istanbul, Turkey.,Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
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Tokaya JP, van den Berg CAT, Luijten PR, Raaijmakers AJE. Explaining RF induced current patterns on implantable medical devices during MRI using the transfer matrix. Med Phys 2021; 48:132-141. [PMID: 32383157 PMCID: PMC7898303 DOI: 10.1002/mp.14225] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 04/08/2020] [Accepted: 04/27/2020] [Indexed: 11/06/2022] Open
Abstract
PURPOSE In this work a simulation study is performed to gain insights in the patterns of induced radiofrequency (RF) currents for various implant-like structures at 1.5 T. The previously introduced transfer matrix (TM) is used to determine why certain current patterns have a tendency to naturally occur. This can benefit current safety assessment techniques and may enable the identification of critical exposure conditions. THEORY AND METHODS The induced current on an elongated implant can be determined by multiplication of the incident electric field along the implant with its TM. The eigenmode spectrum of the TMs for various lengths and various types of implants are determined. The eigenvector with the highest eigenvalue describes the incident electric field pattern that induces the highest current which in turn will lead to highest heating. Subsequently, a statistical probability analysis is performed using a wide range of potential incident electric field distributions in a representative human subject model during a 1.5 T MR exam which are determined by means of electromagnetic FDTD simulations. These incident electric field distributions and the resulting induced current patterns are projected onto eigenvectors of the TM to determine which eigenmodes of the implant dominate the current patterns. RESULTS The eigenvectors of the TM of bare and insulated wires resemble sinusoidal harmonics of a string fixed at both ends similar to the natural-current distribution on thin antennas(1). The currents on implants shorter than 20 cm are generally dominated by the first harmonic (similar to half a sine wave). This is firstly because for these implant lengths (relative to the RF wavelength), the first eigenvalue is more than three times bigger than the second showing the ability of an implant to accommodate one eigenmode better than another. Secondly, the incident electric fields have a high likelihood (≳95,7%) to project predominantly on this first eigenmode. CONCLUSION The eigenmode spectrum of the TM of an implant provides insight into the expected shape of induced current distributions and worst-case exposure conditions. For short implants, the first eigenvector is dominant. In addition, realistic incident electric field distributions project more heavily on this eigenvector. Both effects together cause significant currents to always resemble the dominant eigenmode of the TM for short implants at 1.5 T.
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Affiliation(s)
- Janot P. Tokaya
- Department of RadiotherapyUniversity Medical Center UtrechtP.O. Box 85500Utrecht3508 GANetherlands
| | | | - Peter R. Luijten
- Department of RadiologyUniversity Medical Center UtrechtP.O. Box 85500Utrecht3508 GANetherlands
| | - Alexander J. E. Raaijmakers
- Department of RadiotherapyUniversity Medical Center UtrechtP.O. Box 85500Utrecht3508 GANetherlands
- Department of Biomedical EngineeringEindhoven University of TechnologyEindhoven
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10
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Tsanidis G, Samaras T. Numerical calculation of the radiofrequency transfer function of cochlear implants for assessing deposited power in MRI. Phys Med Biol 2020; 65:175005. [PMID: 32580168 DOI: 10.1088/1361-6560/ab9fc7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The medical imaging of patients with a cochlear implant inside a Magnetic Resonance Imaging (MRI) scanner carries the risk of power deposition in the tissues at the tip of the implant lead, which may result in their heating. In order to assess this risk, ISO/TS 10 974 (2018) describes a methodology (Tier 3 approach) whereby a radiofrequency electrical model for the implant lead in the form of a transfer function is constructed. The construction of the transfer function takes place by assuming that a homogenous medium surrounds the implant, whereas, in reality, implants can traverse various tissues of different electrical properties. The results show that the use of a High Permittivity Medium (HPM) overestimates the Tier 3 calculated deposited power by almost 6 dB, whereas a Low Permittivity Medium (LPM) underestimates it by 9 dB, compared to the in vivo power deposition in three virtual human models, obtained following the Tier 4 approach of ISO/TS 10 974(2018). Since the Tier 3 approach requires less computational resources compared to Tier 4, we suggest its modification with the use of two media (mixed media approach), where implant is immersed. By carefully choosing the media electrical properties, it is possible to calculate power deposition values at the lead tip that differ less than 1 dB from the in vivo ones.
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Affiliation(s)
- George Tsanidis
- Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece. Thessaloniki Software Solutions (THESS) S.A., Technopolis ICT Business Park, Thessaloniki, Greece
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11
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Winter L, Silemek B, Petzold J, Pfeiffer H, Hoffmann W, Seifert F, Ittermann B. Parallel transmission medical implant safety testbed: Real‐time mitigation of RF induced tip heating using time‐domain E‐field sensors. Magn Reson Med 2020; 84:3468-3484. [DOI: 10.1002/mrm.28379] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2019] [Revised: 05/19/2020] [Accepted: 05/22/2020] [Indexed: 12/15/2022]
Affiliation(s)
- Lukas Winter
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Berk Silemek
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Johannes Petzold
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Harald Pfeiffer
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Werner Hoffmann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Frank Seifert
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Bernd Ittermann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
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Winter L, Seifert F, Zilberti L, Murbach M, Ittermann B. MRI‐Related Heating of Implants and Devices: A Review. J Magn Reson Imaging 2020; 53:1646-1665. [DOI: 10.1002/jmri.27194] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Revised: 04/29/2020] [Accepted: 04/30/2020] [Indexed: 12/11/2022] Open
Affiliation(s)
- Lukas Winter
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Frank Seifert
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
| | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica Torino Italy
| | - Manuel Murbach
- ZMT Zurich MedTech AG Zurich Switzerland
- Institute for Molecular Instrumentation and Imaging (i3M) Universidad Politécnica de Valencia (UPV) Valencia Spain
| | - Bernd Ittermann
- Physikalisch‐Technische Bundesanstalt (PTB) Braunschweig and Berlin Germany
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Tokaya JP, Raaijmakers AJ, Luijten PR, Sbrizzi A, van den Berg CA. MRI-based transfer function determination through the transfer matrix by jointly fitting the incident and scattered B1+ field. Magn Reson Med 2020; 83:1081-1095. [PMID: 31631400 PMCID: PMC6899904 DOI: 10.1002/mrm.27974] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2018] [Revised: 08/06/2019] [Accepted: 08/06/2019] [Indexed: 11/13/2022]
Abstract
PURPOSE A purely experimental method for MRI-based transfer function (TF) determination is presented. A TF characterizes the potential for radiofrequency heating of a linear implant by relating the incident tangential electric field to a scattered electric field at its tip. We utilize the previously introduced transfer matrix (TM) to determine transfer functions solely from the MR measurable quantities, that is, the B 1 + and transceive phase distributions. This technique can extend the current practice of phantom-based TF assessment with dedicated experimental setup toward MR-based methods that have the potential to assess the TF in more realistic situations. THEORY AND METHODS An analytical description of the B 1 + magnitude and transceive phase distribution around a wire-like implant was derived based on the TM. In this model, the background field is described using a superposition of spherical and cylindrical harmonics while the transfer matrix is parameterized using a previously introduced attenuated wave model. This analytical description can be used to estimate the transfer matrix and transfer function based on the measured B 1 + distribution. RESULTS The TF was successfully determined for 2 mock-up implants: a 20-cm bare copper wire and a 20-cm insulated copper wire with 10 mm of insulation stripped at both endings in respectively 4 and 3 different trajectories. The measured TFs show a strong correlation with a reference determined from simulations and between the separate experiments with correlation coefficients above 0.96 between all TFs. Compared to the simulated TF, the maximum deviation in the estimated tip field is 9.4% and 12.2% for the bare and insulated wire, respectively. CONCLUSIONS A method has been developed to measure the TF of medical implants using MRI experiments. Jointly fitting the incident and scattered B 1 + distributions with an analytical description based on the transfer matrix enables accurate determination of the TF of 2 test implants. The presented method no longer needs input from simulated data and can therefore, in principle, be used to measure TF's in test animals or corpses.
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Affiliation(s)
- Janot P. Tokaya
- Department of RadiotherapyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Computational Imaging Group for MR Diagnostics & TherapyCenter for Image SciencesUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Alexander J.E. Raaijmakers
- Department of RadiotherapyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Computational Imaging Group for MR Diagnostics & TherapyCenter for Image SciencesUniversity Medical Center UtrechtUtrechtThe Netherlands
- Department of Biomedical EngineeringEindhoven University of TechnologyEindhovenThe Netherlands
| | - Peter R. Luijten
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Alessandro Sbrizzi
- Department of RadiotherapyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Computational Imaging Group for MR Diagnostics & TherapyCenter for Image SciencesUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Cornelis A.T. van den Berg
- Department of RadiotherapyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Computational Imaging Group for MR Diagnostics & TherapyCenter for Image SciencesUniversity Medical Center UtrechtUtrechtThe Netherlands
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Acikel V, Silemek B, Atalar E. Wireless control of induced radiofrequency currents in active implantable medical devices during MRI. Magn Reson Med 2019; 83:2370-2381. [DOI: 10.1002/mrm.28089] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 10/16/2019] [Accepted: 10/29/2019] [Indexed: 11/09/2022]
Affiliation(s)
| | - Berk Silemek
- National Magnetic Resonance Research Center (UMRAM) Bilkent University Ankara Turkey
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM) Bilkent University Ankara Turkey
- Department of Electrical and Electronics Engineering Bilkent University Ankara Turkey
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Aissani S, Laistler E, Felblinger J. [MR safety assessment of active implanted medical devices. German version]. Radiologe 2019; 59:869-874. [PMID: 31190100 DOI: 10.1007/s00117-019-0540-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
BACKGROUND Increasing numbers of patients with active implantable medical devices (AIMDs) require magnetic resonance (MR) examinations. The manufacturers are continuing to improve the MR compatibility of their AIMDs. To this end, a variety of measurement methods and numerical simulations are used to evaluate the risks associated with magnetic resonance imaging (MRI). OBJECTIVE In this article, test methods used to investigate interactions between AIMDs with radio frequency fields and time-varying magnetic gradient fields are reviewed. MATERIALS AND METHODS A literature review of known test methods for radio frequency and gradient field exposure of AIMDs with leads, in particular for neurostimulators, cochlear implants, and implanted infusion pumps, is presented. The state of the art and promising methods are discussed. RESULTS ISO/TS 10974 describes the design of high frequency and gradient injection setups to test conductive materials. A large number of sensor designs have been published to measure the induced voltages and currents through radio frequency and gradient fields and for monitoring AIMDs during MR examinations in in vitro tests. CONCLUSION The test methods should be planned to be as conservative as possible to cover the worst case scenario. However, in vitro measurements and computer simulation are far from being able to cover all possible configurations in their complexity and uniqueness. For safer MR examinations, current research recommends in vivo testing prior to MR, parallel radiofrequency transmission techniques, and new sequences with reduced energy input in the presence of AIMDs.
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Affiliation(s)
- Sarra Aissani
- IADI, U947, INSERM, Université de Lorraine, CHRU de Nancy Brabois, Bâtiment Recherche, Rue du Morvan, 54511, Nancy, Frankreich
| | - Elmar Laistler
- Zentrum für Medizinische Physik und Biomedizinische Technik, Medizinische Universität Wien, Wien, Österreich.,Exzellenzzentrum Hochfeld MR, Medizinische Universität Wien, Wien, Österreich
| | - Jacques Felblinger
- IADI, U947, INSERM, Université de Lorraine, CHRU de Nancy Brabois, Bâtiment Recherche, Rue du Morvan, 54511, Nancy, Frankreich. .,CIC 1433 Innovation Technologique, INSERM, CHRU Nancy Brabois, Nancy, Frankreich.
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Abstract
BACKGROUND Increasing numbers of patients with active implantable medical devices (AIMDs) require magnetic resonance (MR) examinations. The manufacturers are continuing to improve the MR compatibility of their AIMDs. To this end, a variety of measurement methods and numerical simulations are used to evaluate the risks associated with magnetic resonance imaging (MRI). OBJECTIVE In this article, test methods used to investigate interactions between AIMDs with radio frequency fields and time-varying magnetic gradient fields are reviewed. MATERIALS AND METHODS A literature review of known test methods for radio frequency and gradient field exposure of AIMDs with leads, in particular for neurostimulators, cochlear implants, and implanted infusion pumps, is presented. The state of the art and promising methods are discussed. RESULTS ISO/TS 10974 describes the design of high frequency and gradient injection setups to test conductive materials. A large number of sensor designs have been published to measure the induced voltages and currents through radio frequency and gradient fields and for monitoring AIMDs during MR examinations in in vitro tests. CONCLUSION The test methods should be planned to be as conservative as possible to cover the worst case scenario. However, in vitro measurements and computer simulation are far from being able to cover all possible configurations in their complexity and uniqueness. For safer MR examinations, current research recommends in vivo testing prior to MR, parallel radiofrequency transmission techniques, and new sequences with reduced energy input in the presence of AIMDs.
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Affiliation(s)
- Sarra Aissani
- IADI, U1254, INSERM, Université de Lorraine, CHRU de Nancy Brabois, Bâtiment Recherche (anciennement EFS), Rez-de-Chaussé, Rue du Morvan, 54511, Nancy, France
| | - Elmar Laistler
- Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.,MR Centre of Excellence, Medical University of Vienna, Vienna, Austria
| | - Jacques Felblinger
- IADI, U1254, INSERM, Université de Lorraine, CHRU de Nancy Brabois, Bâtiment Recherche (anciennement EFS), Rez-de-Chaussé, Rue du Morvan, 54511, Nancy, France. .,CIC 1433 Innovation Technologique, INSERM, CHRU Nancy Brabois, Nancy, France.
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Özen AC, Lottner T, Bock M. Safety of active catheters in MRI: Termination impedance versus RF‐induced heating. Magn Reson Med 2018; 81:1412-1423. [DOI: 10.1002/mrm.27481] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 06/08/2018] [Accepted: 07/15/2018] [Indexed: 11/06/2022]
Affiliation(s)
- Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
- German Cancer Consortium Partner Site Freiburg, German Cancer Research Center (DKFZ) Heidelberg Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center ‐ University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany
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Tokaya JP, Raaijmakers AJE, Luijten PR, van den Berg CAT. MRI-based, wireless determination of the transfer function of a linear implant: Introduction of the transfer matrix. Magn Reson Med 2018; 80:2771-2784. [PMID: 29687916 PMCID: PMC6220769 DOI: 10.1002/mrm.27218] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 03/23/2018] [Accepted: 03/24/2018] [Indexed: 12/17/2022]
Abstract
PURPOSE We introduce the transfer matrix (TM) that makes MR-based wireless determination of transfer functions (TFs) possible. TFs are implant specific measures for RF-safety assessment of linear implants. The TF relates an incident tangential electric field on an implant to a scattered electric field at its tip that generally governs local heating. The TM extends this concept and relates an incident tangential electric field to a current distribution in the implant therewith characterizing the RF response along the entire implant. The TM is exploited to measure TFs with MRI without hardware alterations. THEORY AND METHODS A model of rightward and leftward propagating attenuated waves undergoing multiple reflections is used to derive an analytical expression for the TM. This allows parameterization of the TM of generic implants, e.g., (partially) insulated single wires, in a homogeneous medium in a few unknowns that simultaneously describe the TF. These unknowns can be determined with MRI making it possible to measure the TM and, therefore, also the TF. RESULTS The TM is able to predict an induced current due to an incident electric field and can be accurately parameterized with a limited number of unknowns. Using this description the TF is determined accurately (with a Pearson correlation coefficient R ≥ 0.9 between measurements and simulations) from MRI acquisitions. CONCLUSION The TM enables measuring of TFs with MRI of the tested generic implant models. The MR-based method does not need hardware alterations and is wireless hence making TF determination in more realistic scenarios conceivable.
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Affiliation(s)
- Janot P Tokaya
- Department of Radiotherapy, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Peter R Luijten
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
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