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Petzold J, Schmitter S, Silemek B, Winter L, Speck O, Ittermann B, Seifert F. Investigation of alternative RF power limit control methods for 0.5T, 1.5T, and 3T parallel transmission cardiac imaging: A simulation study. Magn Reson Med 2024; 91:1659-1675. [PMID: 38031517 DOI: 10.1002/mrm.29932] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2023] [Revised: 10/09/2023] [Accepted: 10/31/2023] [Indexed: 12/01/2023]
Abstract
PURPOSE To investigate safety and performance aspects of parallel-transmit (pTx) RF control-modes for a body coil atB 0 ≤ 3 T $$ {B}_0\le 3\mathrm{T} $$ . METHODS Electromagnetic simulations of 11 human voxel models in cardiac imaging position were conducted forB 0 = 0.5 T $$ {B}_0=0.5\mathrm{T} $$ ,1.5 T $$ 1.5\mathrm{T} $$ and3 T $$ 3\mathrm{T} $$ and a body coil with a configurable number of transmit channels (1, 2, 4, 8, 16). Three safety modes were considered: the 'SAR-controlled mode' (SCM), where specific absorption rate (SAR) is limited directly, a 'phase agnostic SAR-controlled mode' (PASCM), where phase information is neglected, and a 'power-controlled mode' (PCM), where the voltage amplitude for each channel is limited. For either mode, safety limits were established based on a set of 'anchor' simulations and then evaluated in 'target' simulations on previously unseen models. The comparison allowed to derive safety factors accounting for varying patient anatomies. All control modes were compared in terms of theB 1 + $$ {B}_1^{+} $$ amplitude and homogeneity they permit under their respective safety requirements. RESULTS Large safety factors (approximately five) are needed if only one or two anchor models are investigated but they shrink with increasing number of anchors. The achievableB 1 + $$ {B}_1^{+} $$ is highest for SCM but this advantage is reduced when the safety factor is included. PCM appears to be more robust against variations of subjects. PASCM performance is mostly in between SCM and PCM. Compared to standard circularly polarized (CP) excitation, pTx offers minorB 1 + $$ {B}_1^{+} $$ improvements if local SAR limits are always enforced. CONCLUSION PTx body coils can safely be used atB 0 ≤ 3 T $$ {B}_0\le 3\mathrm{T} $$ . Uncertainties in patient anatomy must be accounted for, however, by simulating many models.
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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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Silemek B, Seifert F, Petzold J, Brühl R, Ittermann B, Winter L. Wirelessly interfacing sensor-equipped implants and MR scanners for improved safety and imaging. Magn Reson Med 2023; 90:2608-2626. [PMID: 37533167 DOI: 10.1002/mrm.29818] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 07/12/2023] [Accepted: 07/13/2023] [Indexed: 08/04/2023]
Abstract
PURPOSE To investigate a novel reduced RF heating method for imaging in the presence of active implanted medical devices (AIMDs) which employs a sensor-equipped implant that provides wireless feedback. METHODS The implant, consisting of a generator case and a lead, measures RF-inducedE $$ E $$ -fields at the implant tip using a simple sensor in the generator case and transmits these values wirelessly to the MR scanner. Based on the sensor signal alone, parallel transmission (pTx) excitation vectors were calculated to suppress tip heating and maintain image quality. A sensor-based imaging metric was introduced to assess the image quality. The methodology was studied at 7T in testbed experiments, and at a 3T scanner in an ASTM phantom containing AIMDs instrumented with six realistic deep brain stimulation (DBS) lead configurations adapted from patients. RESULTS The implant successfully measured RF-inducedE $$ E $$ -fields (Pearson correlation coefficient squared [R2 ] = 0.93) and temperature rises (R2 = 0.95) at the implant tip. The implant acquired the relevant data needed to calculate the pTx excitation vectors and transmitted them wirelessly to the MR scanner within a single shot RF sequence (<60 ms). Temperature rises for six realistic DBS lead configurations were reduced to 0.03-0.14 K for heating suppression modes compared to 0.52-3.33 K for the worst-case heating, while imaging quality remained comparable (five of six lead imaging scores were ≥0.80/1.00) to conventional circular polarization (CP) images. CONCLUSION Implants with sensors that can communicate with an MR scanner can substantially improve safety for patients in a fast and automated manner, easing the current burden for MR personnel.
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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
| | - Rüdiger Brühl
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, 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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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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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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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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Singh R, Bathaei MJ, Istif E, Beker L. A Review of Bioresorbable Implantable Medical Devices: Materials, Fabrication, and Implementation. Adv Healthc Mater 2020; 9:e2000790. [PMID: 32790033 DOI: 10.1002/adhm.202000790] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2020] [Revised: 06/22/2020] [Indexed: 12/15/2022]
Abstract
Implantable medical devices (IMDs) are designed to sense specific parameters or stimulate organs and have been actively used for treatment and diagnosis of various diseases. IMDs are used for long-term disease screening or treatments and cannot be considered for short-term applications since patients need to go through a surgery for retrieval of the IMD. Advances in bioresorbable materials has led to the development of transient IMDs that can be resorbed by bodily fluids and disappear after a certain period. These devices are designed to be implanted in the adjacent of the targeted tissue for predetermined times with the aim of measurement of pressure, strain, or temperature, while the bioelectronic devices stimulate certain tissues. They enable opportunities for monitoring and treatment of acute diseases. To realize such transient and miniaturized devices, researchers utilize a variety of materials, novel fabrication methods, and device design strategies. This review discusses potential bioresorbable materials for each component in an IMD followed by programmable degradation and safety standards. Then, common fabrication methods for bioresorbable materials are introduced, along with challenges. The final section provides representative examples of bioresorbable IMDs for various applications with an emphasis on materials, device functionality, and fabrication methods.
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Affiliation(s)
- Rahul Singh
- Department of Mechanical Engineering Koç University Rumelifeneri Yolu, Sarıyer Istanbul 34450 Turkey
| | - Mohammad Javad Bathaei
- Department of Biomedical Sciences and Engineering Koç University Rumelifeneri Yolu, Sarıyer Istanbul 34450 Turkey
| | - Emin Istif
- Department of Mechanical Engineering Koç University Rumelifeneri Yolu, Sarıyer Istanbul 34450 Turkey
| | - Levent Beker
- Department of Mechanical Engineering Koç University Rumelifeneri Yolu, Sarıyer Istanbul 34450 Turkey
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Lu D, Yan Y, Avila R, Kandela I, Stepien I, Seo M, Bai W, Yang Q, Li C, Haney CR, Waters EA, MacEwan MR, Huang Y, Ray WZ, Rogers JA. Bioresorbable, Wireless, Passive Sensors as Temporary Implants for Monitoring Regional Body Temperature. Adv Healthc Mater 2020; 9:e2000942. [PMID: 32597568 DOI: 10.1002/adhm.202000942] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Indexed: 12/26/2022]
Abstract
Measurements of regional internal body temperatures can yield important information in the diagnosis of immune response-related anomalies, for precisely managing the effects of hyperthermia and hypothermia therapies and monitoring other transient body processes such as those associated with wound healing. Current approaches rely on permanent implants that require extraction surgeries after the measurements are no longer needed. Emerging classes of bioresorbable sensors eliminate the requirements for extraction, but their use of percutaneous wires for data acquisition leads to risks for infection at the suture site. As an alternative, a battery-free, wireless implantable device is reported here, which is constructed entirely with bioresorbable materials for monitoring regional internal body temperatures over clinically relevant timeframes. Ultimately, these devices disappear completely in the body through natural processes. In vivo demonstrations indicate stable operation as subcutaneous and intracranial implants in rat models for up to 4 days. Potential applications include monitoring of healing cascades associated with surgical wounds, recovery processes following internal injuries, and the progression of thermal therapies for various conditions.
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Affiliation(s)
- Di Lu
- Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA
| | - Ying Yan
- Department of Neurological Surgery Washington University School of Medicine St Louis MO 63110 USA
| | - Raudel Avila
- Department of Materials Science and Engineering Northwestern University Evanston IL 60208 USA
- Departments of Mechanical Engineering and Civil and Environmental Engineering Northwestern University Evanston IL 60208 USA
| | - Irawati Kandela
- Center for Developmental Therapeutics Northwestern University Evanston IL 60208 USA
- Chemistry Life Processes Institute Northwestern University Evanston IL 60208 USA
| | - Iwona Stepien
- Center for Developmental Therapeutics Northwestern University Evanston IL 60208 USA
- Chemistry Life Processes Institute Northwestern University Evanston IL 60208 USA
| | - Min‐Ho Seo
- Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA
| | - Wubin Bai
- Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA
| | - Quansan Yang
- Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA
| | - Chenhang Li
- Department of Materials Science and Engineering Northwestern University Evanston IL 60208 USA
- Departments of Mechanical Engineering and Civil and Environmental Engineering Northwestern University Evanston IL 60208 USA
| | - Chad R. Haney
- Chemistry Life Processes Institute Northwestern University Evanston IL 60208 USA
- Center for Advanced Molecular Imaging Northwestern University Evanston IL 60208 USA
| | - Emily A. Waters
- Chemistry Life Processes Institute Northwestern University Evanston IL 60208 USA
- Center for Advanced Molecular Imaging Northwestern University Evanston IL 60208 USA
| | - Matthew R. MacEwan
- Department of Neurological Surgery Washington University School of Medicine St Louis MO 63110 USA
| | - Yonggang Huang
- Department of Materials Science and Engineering Northwestern University Evanston IL 60208 USA
- Departments of Mechanical Engineering and Civil and Environmental Engineering Northwestern University Evanston IL 60208 USA
| | - Wilson Z. Ray
- Department of Neurological Surgery Washington University School of Medicine St Louis MO 63110 USA
| | - John A. Rogers
- Center for Bio‐Integrated Electronics Northwestern University Evanston IL 60208 USA
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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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Özen AC, Silemek B, Lottner T, Atalar E, Bock M. MR safety watchdog for active catheters: Wireless impedance control with real-time feedback. Magn Reson Med 2020; 84:1048-1060. [PMID: 31961965 DOI: 10.1002/mrm.28153] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Revised: 11/29/2019] [Accepted: 12/09/2019] [Indexed: 12/13/2022]
Abstract
PURPOSE To dynamically minimize radiofrequency (RF)-induced heating of an active catheter through an automatic change of the termination impedance. METHODS A prototype wireless module was designed that modifies the input impedance of an active catheter to keep the temperature rise during MRI below a threshold, ΔTmax . The wireless module (MR safety watchdog; MRsWD) measures the local temperature at the catheter tip using either a built-in thermistor or external data from a fiber-optical thermometer. It automatically changes the catheter input impedance until the temperature rise during MRI is minimized. If ΔTmax is exceeded, RF transmission is blocked by a feedback system. RESULTS The thermistor and fiber-optical thermometer provided consistent temperature data in a phantom experiment. During MRI, the MRsWD was able to reduce the maximum temperature rise by 25% when operated in real-time feedback mode. CONCLUSION This study demonstrates the technical feasibility of an MRsWD as an alternative or complementary approach to reduce RF-induced heating of active interventional devices. The automatic MRsWD can reduce heating using direct temperature measurements at the tip of the catheter. Given that temperature measurements are intrinsically slow, for a clinical implementation, a faster feedback parameter would be required such as the RF currents along the catheter or scattered electric fields at the tip.
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Affiliation(s)
- Ali Caglar Özen
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany.,Faculty of Medicine, University of Freiburg, Freiburg, Germany.,German Consortium for Translational Cancer Research Partner Site Freiburg, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Berk Silemek
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
| | - Ergin Atalar
- National Magnetic Resonance Research Center (UMRAM), Bilkent University, Ankara, Turkey.,Department of Electrical and Electronics Engineering, Bilkent University, Ankara, Turkey
| | - Michael Bock
- Department of Radiology, Medical Physics, Medical Center - University of Freiburg, Freiburg, Germany
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11
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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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12
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Abstract
Flexible sensors have the potential to be seamlessly applied to soft and irregularly shaped surfaces such as the human skin or textile fabrics. This benefits conformability dependant applications including smart tattoos, artificial skins and soft robotics. Consequently, materials and structures for innovative flexible sensors, as well as their integration into systems, continue to be in the spotlight of research. This review outlines the current state of flexible sensor technologies and the impact of material developments on this field. Special attention is given to strain, temperature, chemical, light and electropotential sensors, as well as their respective applications.
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