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Karasan E, Hammerschmidt A, Arias AC, Taracila V, Robb F, Lustig M. Caterpillar traps: A highly flexible, distributed system of toroidal cable traps. Magn Reson Med 2023; 89:2471-2484. [PMID: 36695296 PMCID: PMC10278796 DOI: 10.1002/mrm.29584] [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: 06/29/2022] [Revised: 12/05/2022] [Accepted: 12/29/2022] [Indexed: 01/26/2023]
Abstract
PURPOSE Coil arrays are connected to the main MRI system with long, shielded coaxial cables. RF coupling of these cables to the main transmit coil can cause high shield currents, which pose risks of heating and RF burns. High-blocking resonant RF traps are placed at distinct positions along cables to mitigate these currents. Traditional traps are designed to be stiff to avoid changes in their resonant frequency, hindering the overall system flexibility. Instead of using a few high-blocking traps, we propose the use of caterpillar traps-a distributed system of small, elastic traps that cover the full length of cables. METHODS We leverage an array of resonant toroids as traps, forming a caterpillar-like structure whereby bending only impacts individual traps minimally. Benchtop measurements are used to determine the blocking of caterpillar traps and show their robustness to bending. We also compare an anterior array system cable covered with caterpillar traps to a commercial cable with B1 + and heating measurements. RESULTS Benchtop experiments with caterpillar traps demonstrate high robustness to bending. B1 + mapping experiments of an anterior array cable show improved blocking and flexibility compared to a commercial cable. CONCLUSION Caterpillar traps provide sufficient attenuation to shield currents while allowing cable flexibility. Our distributed design can provide high blocking efficiency at different positions and orientations, even in cases where commercial cable traps cannot.
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Affiliation(s)
- Ekin Karasan
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA
| | | | - Ana Claudia Arias
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA
| | | | | | - Michael Lustig
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, CA, USA
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2
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Yildirim DK, Uzun D, Bruce CG, Khan JM, Rogers T, Schenke WH, Ramasawmy R, Campbell-Washburn A, Herzka D, Lederman RJ, Kocaturk O. An interventional MRI guidewire combining profile and tip conspicuity for catheterization at 0.55T. Magn Reson Med 2023; 89:845-858. [PMID: 36198118 PMCID: PMC9712240 DOI: 10.1002/mrm.29466] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 08/04/2022] [Accepted: 09/02/2022] [Indexed: 12/13/2022]
Abstract
PURPOSE We describe a clinical grade, "active", monopole antenna-based metallic guidewire that has a continuous shaft-to-tip image profile, a pre-shaped tip-curve, standard 0.89 mm (0.035″) outer diameter, and a detachable connector for catheter exchange during cardiovascular catheterization at 0.55T. METHODS Electromagnetic simulations were performed to characterize the magnetic field around the antenna whip for continuous tip visibility. The active guidewire was manufactured using medical grade materials in an ISO Class 7 cleanroom. RF-induced heating of the active guidewire prototype was tested in one gel phantom per ASTM 2182-19a, alone and in tandem with clinical metal-braided catheters. Real-time MRI visibility was tested in one gel phantom and in-vivo in two swine. Mechanical performance was compared with commercial equivalents. RESULTS The active guidewire provided continuous "profile" shaft and tip visibility in-vitro and in-vivo, analogous to guidewire shaft-and-tip profiles under X-ray. The MRI signal signature matched simulation results. Maximum unscaled RF-induced temperature rise was 5.2°C and 6.5°C (3.47 W/kg local background specific absorption rate), alone and in tandem with a steel-braided catheter, respectively. Mechanical characteristics matched commercial comparator guidewires. CONCLUSION The active guidewire was clearly visible via real-time MRI at 0.55T and exhibits a favorable geometric sensitivity profile depicting the guidewire continuously from shaft-to-tip including a unique curved-tip signature. RF-induced heating is clinically acceptable. This design allows safe device navigation through luminal structures and heart chambers. The detachable connector allows delivery and exchange of cardiovascular catheters while maintaining guidewire position. This enhanced guidewire design affords the expected performance of X-ray guidewires during human MRI catheterization.
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Affiliation(s)
- Dursun Korel Yildirim
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Dogangun Uzun
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
- Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey
| | - Christopher G. Bruce
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Jaffar M. Khan
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Toby Rogers
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - William H. Schenke
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Rajiv Ramasawmy
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Adrienne Campbell-Washburn
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Daniel Herzka
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Robert J. Lederman
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, MD, USA
| | - Ozgur Kocaturk
- Institute of Biomedical Engineering, Bogazici University, Istanbul, Turkey
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Kilbride BF, Narsinh KH, Jordan CD, Mueller K, Moore T, Martin AJ, Wilson MW, Hetts SW. MRI-guided endovascular intervention: current methods and future potential. Expert Rev Med Devices 2022; 19:763-778. [PMID: 36373162 PMCID: PMC9869980 DOI: 10.1080/17434440.2022.2141110] [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: 04/06/2022] [Accepted: 10/25/2022] [Indexed: 11/16/2022]
Abstract
INTRODUCTION Image-guided endovascular interventions, performed using the insertion and navigation of catheters through the vasculature, have been increasing in number over the years, as minimally invasive procedures continue to replace invasive surgical procedures. Such endovascular interventions are almost exclusively performed under x-ray fluoroscopy, which has the best spatial and temporal resolution of all clinical imaging modalities. Magnetic resonance imaging (MRI) offers unique advantages and could be an attractive alternative to conventional x-ray guidance, but also brings with it distinctive challenges. AREAS COVERED In this review, the benefits and limitations of MRI-guided endovascular interventions are addressed, systems and devices for guiding such interventions are summarized, and clinical applications are discussed. EXPERT OPINION MRI-guided endovascular interventions are still relatively new to the interventional radiology field, since significant technical hurdles remain to justify significant costs and demonstrate safety, design, and robustness. Clinical applications of MRI-guided interventions are promising but their full potential may not be realized until proper tools designed to function in the MRI environment are available. Translational research and further preclinical studies are needed before MRI-guided interventions will be practical in a clinical interventional setting.
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Affiliation(s)
- Bridget F. Kilbride
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | - Kazim H. Narsinh
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | | | | | - Teri Moore
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | - Alastair J. Martin
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | - Mark W. Wilson
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
| | - Steven W. Hetts
- Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA
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4
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Godinez F, Tomi-Tricot R, Delcey M, Williams SE, Mooiweer R, Quesson B, Razavi R, Hajnal JV, Malik SJ. Interventional cardiac MRI using an add-on parallel transmit MR system: In vivo experience in sheep. Magn Reson Med 2021; 86:3360-3372. [PMID: 34286866 DOI: 10.1002/mrm.28931] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2021] [Revised: 06/15/2021] [Accepted: 06/28/2021] [Indexed: 12/19/2022]
Abstract
PURPOSE We present in vivo testing of a parallel transmit system intended for interventional MR-guided cardiac procedures. METHODS The parallel transmit system was connected in-line with a conventional 1.5 Tesla MRI system to transmit and receive on an 8-coil array. The system used a current sensor for real-time feedback to achieve real-time current control by determining coupling and null modes. Experiments were conducted on 4 Charmoise sheep weighing 33.9-45.0 kg with nitinol guidewires placed under X-ray fluoroscopy in the atrium or ventricle of the heart via the femoral vein. Heating tests were done in vivo and post-mortem with a high RF power imaging sequence using the coupling mode. Anatomical imaging was done using a combination of null modes optimized to produce a useable B1 field in the heart. RESULTS Anatomical imaging produced cine images of the heart comparable in quality to imaging with the quad mode (all channels with the same amplitude and phase). Maximum observed temperature increases occurred when insulation was stripped from the wire tip. These were 4.1℃ and 0.4℃ for the coupling mode and null modes, respectively for the in vivo case; increasing to 6.0℃ and 1.3℃, respectively for the ex vivo case, because cooling from blood flow is removed. Heating < 0.1℃ was observed when insulation was not stripped from guidewire tips. In all tests, the parallel transmit system managed to reduce the temperature at the guidewire tip. CONCLUSION We have demonstrated the first in vivo usage of an auxiliary parallel transmit system employing active feedback-based current control for interventional MRI with a conventional MRI scanner.
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Affiliation(s)
- Felipe Godinez
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Raphael Tomi-Tricot
- MR Research Collaborations, Siemens Healthcare Limited, Frimley, United Kingdom
| | - Marylène Delcey
- Centre de Recherche Cardio, Thoracique de Bordeaux/IHU Liryc, INSERM U1045-University of Bordeaux, Pessac, France.,Siemens Healthcare, Saint-Denis, France
| | - Steven E Williams
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Ronald Mooiweer
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Bruno Quesson
- Centre de Recherche Cardio, Thoracique de Bordeaux/IHU Liryc, INSERM U1045-University of Bordeaux, Pessac, France
| | - Reza Razavi
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Joseph V Hajnal
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Shaihan J Malik
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom.,Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
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5
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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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6
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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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7
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Dixit N, Pauly JM, Scott GC. Thermo‐acoustic ultrasound for noninvasive temperature monitoring at lead tips during MRI. Magn Reson Med 2019; 84:1035-1047. [DOI: 10.1002/mrm.28152] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2019] [Revised: 11/14/2019] [Accepted: 12/09/2019] [Indexed: 12/29/2022]
Affiliation(s)
- Neerav Dixit
- Department of Electrical Engineering Stanford University Stanford CAUSA
| | - John M. Pauly
- Department of Electrical Engineering Stanford University Stanford CAUSA
| | - Greig C. Scott
- Department of Electrical Engineering Stanford University Stanford CAUSA
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8
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Godinez F, Scott G, Padormo F, Hajnal JV, Malik SJ. Safe guidewire visualization using the modes of a PTx transmit array MR system. Magn Reson Med 2019; 83:2343-2355. [PMID: 31722119 PMCID: PMC7048617 DOI: 10.1002/mrm.28069] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 10/16/2019] [Accepted: 10/16/2019] [Indexed: 02/06/2023]
Abstract
Purpose MRI‐guided cardiovascular intervention using standard metal guidewires can produce focal tissue heating caused by induced radiofrequency guidewire currents. It has been shown that safe operation is made possible by using parallel transmit radiofrequency coils driven in the null current mode, which does not induce radiofrequency currents and hence allows safe tissue visualization. We propose that the maximum current modes, usually considered unsafe, be used at very low power levels to visualize conductive wires, and we investigate pulse sequences best suited for this application. Methods Spoiled gradient echo, balanced steady‐state free precession, and turbo spin echo sequences were evaluated for their ability to visualize a conductive guidewire embedded in a gel phantom when run in maximum current modes at very low power level. Temperature at the guidewire tip was monitored for safety assessment. Results Excellent guidewire visualization could be achieved using maximum current modes excitation, with the turbo spin echo sequence giving the best image quality. Although turbo spin echo is usually considered to be a high‐power sequence, our method reduced all pulses to 1% amplitude (0.01% power), and heating was not detected. In addition, visualization of background tissue can be achieved using null current mode, also with no recorded heating at the guidewire tip even when running at 100% (reported) specific absorption rate. Conclusion Parallel transmit is a promising approach for both guidewire and tissue visualization using maximum and null current modes, respectively, for interventional cardiac MRI. Such systems can switch excitation mode instantaneously, allowing for flexible integration into interactive sequences.
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Affiliation(s)
- Felipe Godinez
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Greig Scott
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | | | - Joseph V Hajnal
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
| | - Shaihan J Malik
- School of Biomedical Engineering and Imaging Sciences, King's College London, London, United Kingdom
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9
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Griffin GH, Ramanan V, Barry J, Wright GA. Toward in vivo quantification of induced RF currents on long thin conductors. Magn Reson Med 2018; 80:1922-1934. [PMID: 29656481 DOI: 10.1002/mrm.27195] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2017] [Revised: 01/25/2018] [Accepted: 03/06/2018] [Indexed: 11/07/2022]
Abstract
PURPOSE Most MR-guided catheter-based procedures, and imaging of patients with implanted medical devices, are currently contraindicated due to a significant risk of heating associated with induced RF currents. The induced RF current produces a corresponding artifact which can be used to remotely characterize current and safely predict RF heating. Application of this remote technique in vivo to safely quantify RF heating risk may allow for execution of many scans currently contraindicated. Sources of phase other than induced RF current may present difficulty in practical in vivo. METHODS A custom ultra-short echo time (UTE) sequence was developed to minimize unwanted phase contributions. A phantom experiment was performed to compare current characterization using a stock gradient-echo (GRE) sequence and the custom UTE sequence following calibration of the temperature measurement apparatus using a previously published heating prediction technique. Animal experiments were used to investigate the feasibility of using the UTE sequence to quantify RF heating. RESULTS Current characterization and heating prediction with a stock GRE sequence was equivalent to that with the custom UTE sequence. Heating measurements and image-based predictions in animal experiments agreed within error in all experiments. CONCLUSION Through comparison of measured heating and image-based prediction, feasibility of using a custom UTE sequence to quantify RF heating risk in vivo was demonstrated.
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Affiliation(s)
| | - Venkat Ramanan
- Imaging Research, Sunnybrook Research Institute, Toronto, Canada
| | - Jennifer Barry
- Imaging Research, Sunnybrook Research Institute, Toronto, Canada
| | - Graham A Wright
- Imaging Research, Sunnybrook Research Institute, Toronto, Canada
- Department of Medical Biophysics, Faculty of Medicine, University of Toronto, Toronto, Canada
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10
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Dixit N, Stang PP, Pauly JM, Scott GC. Thermo-Acoustic Ultrasound for Detection of RF-Induced Device Lead Heating in MRI. IEEE TRANSACTIONS ON MEDICAL IMAGING 2018; 37:536-546. [PMID: 29053449 PMCID: PMC5942199 DOI: 10.1109/tmi.2017.2764425] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Patients who have implanted medical devices with long conductive leads are often restricted from receiving MRI scans due to the danger of RF-induced heating near the lead tips. Phantom studies have shown that this heating varies significantly on a case-by-case basis, indicating that many patients with implanted devices can receive clinically useful MRI scans without harm. However, the difficulty of predicting RF-induced lead tip heating prior to scanning prevents numerous implant recipients from being scanned. Here, we demonstrate that thermo-acoustic ultrasound (TAUS) has the potential to be utilized for a pre-scan procedure assessing the risk of RF-induced lead tip heating in MRI. A system was developed to detect TAUS signals by four different TAUS acquisition methods. We then integrated this system with an MRI scanner and detected a peak in RF power absorption near the tip of a model lead when transmitting from the scanner's body coil. We also developed and experimentally validated simulations to characterize the thermo-acoustic signal generated near lead tips. These results indicate that TAUS is a promising method for assessing RF implant safety, and with further development, a TAUS pre-scan could allow many more patients to have access to MRI scans of significant clinical value.
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11
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Alipour A, Gokyar S, Algin O, Atalar E, Demir HV. An inductively coupled ultra-thin, flexible, and passive RF resonator for MRI marking and guiding purposes: Clinical feasibility. Magn Reson Med 2017; 80:361-370. [PMID: 29148092 DOI: 10.1002/mrm.26996] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 09/17/2017] [Accepted: 10/15/2017] [Indexed: 12/20/2022]
Abstract
PURPOSE The purpose of this study is to develop a wireless, flexible, ultra-thin, and passive radiofrequency-based MRI resonant fiducial marker, and to validate its feasibility in a phantom model and several body regions. METHODS Standard microfabrication processing was used to fabricate the resonant marker. The proposed marker consists of two metal traces in the shape of a square with an edge length of 8 mm, with upper and lower traces connected to each other by a metalized via. A 3T MRI fiducial marking procedure was tested in phantom and ex vivo, and then the marker's performance was evaluated in an MRI experiment using humans. The radiofrequency safety was also tested using temperature sensors in the proximity of the resonator. RESULTS A flexible resonator with a thickness of 115 μm and a dimension of 8 × 8 mm was obtained. The experimental results in the phantom show that at low background flip angles (6-18°), the resonant marker enables precise and rapid visibility, with high marker-to-background contrast and signal-to-noise ratio improvement of greater than 10 in the vicinity of the marker. Temperature analysis showed a specific absorption ratio gain of 1.3. Clinical studies further showed a successful biopsy procedure using the fiducial marking functionality of our device. CONCLUSIONS The ultra-thin and flexible structure of this wireless flexible radiofrequency resonant marker offers effective and safe MR visualization with high feasibility for anatomic marking and guiding at various regions of the body. Magn Reson Med 80:361-370, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Akbar Alipour
- Department of Electrical and Electronics Engineering, National Magnetic Resonance Research Center (UMRAM) National Nanotechnology Research Center and Institute of Material Science and Nanotechnology (UNAM) Department of Physics, Bilkent University, Bilkent, Ankara, Turkey
| | - Sayim Gokyar
- Department of Electrical and Electronics Engineering, National Magnetic Resonance Research Center (UMRAM) National Nanotechnology Research Center and Institute of Material Science and Nanotechnology (UNAM) Department of Physics, Bilkent University, Bilkent, Ankara, Turkey
| | - Oktay Algin
- Department of Electrical and Electronics Engineering, National Magnetic Resonance Research Center (UMRAM) National Nanotechnology Research Center and Institute of Material Science and Nanotechnology (UNAM) Department of Physics, Bilkent University, Bilkent, Ankara, Turkey.,Department of Radiology, Ankara Ataturk Training and Research Hospital, Ankara, Turkey
| | - Ergin Atalar
- Department of Electrical and Electronics Engineering, National Magnetic Resonance Research Center (UMRAM) National Nanotechnology Research Center and Institute of Material Science and Nanotechnology (UNAM) Department of Physics, Bilkent University, Bilkent, Ankara, Turkey
| | - Hilmi Volkan Demir
- Department of Electrical and Electronics Engineering, National Magnetic Resonance Research Center (UMRAM) National Nanotechnology Research Center and Institute of Material Science and Nanotechnology (UNAM) Department of Physics, Bilkent University, Bilkent, Ankara, Turkey.,LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, School of Mathematical and Physical Sciences, Nanyang Technological University, Singapore
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12
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Campbell-Washburn AE, Tavallaei MA, Pop M, Grant EK, Chubb H, Rhode K, Wright GA. Real-time MRI guidance of cardiac interventions. J Magn Reson Imaging 2017; 46:935-950. [PMID: 28493526 PMCID: PMC5675556 DOI: 10.1002/jmri.25749] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2017] [Accepted: 03/29/2017] [Indexed: 11/09/2022] Open
Abstract
Cardiac magnetic resonance imaging (MRI) is appealing to guide complex cardiac procedures because it is ionizing radiation-free and offers flexible soft-tissue contrast. Interventional cardiac MR promises to improve existing procedures and enable new ones for complex arrhythmias, as well as congenital and structural heart disease. Guiding invasive procedures demands faster image acquisition, reconstruction and analysis, as well as intuitive intraprocedural display of imaging data. Standard cardiac MR techniques such as 3D anatomical imaging, cardiac function and flow, parameter mapping, and late-gadolinium enhancement can be used to gather valuable clinical data at various procedural stages. Rapid intraprocedural image analysis can extract and highlight critical information about interventional targets and outcomes. In some cases, real-time interactive imaging is used to provide a continuous stream of images displayed to interventionalists for dynamic device navigation. Alternatively, devices are navigated relative to a roadmap of major cardiac structures generated through fast segmentation and registration. Interventional devices can be visualized and tracked throughout a procedure with specialized imaging methods. In a clinical setting, advanced imaging must be integrated with other clinical tools and patient data. In order to perform these complex procedures, interventional cardiac MR relies on customized equipment, such as interactive imaging environments, in-room image display, audio communication, hemodynamic monitoring and recording systems, and electroanatomical mapping and ablation systems. Operating in this sophisticated environment requires coordination and planning. This review provides an overview of the imaging technology used in MRI-guided cardiac interventions. Specifically, this review outlines clinical targets, standard image acquisition and analysis tools, and the integration of these tools into clinical workflow. LEVEL OF EVIDENCE 1 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:935-950.
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Affiliation(s)
- Adrienne E Campbell-Washburn
- Laboratory of Imaging Technology, Biochemistry and Biophysics Center, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Mohammad A Tavallaei
- Physical Sciences Platform and Schulich Heart Program, Sunnybrook Research Institute, Toronto, Ontario, Canada
- Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Mihaela Pop
- Physical Sciences Platform and Schulich Heart Program, Sunnybrook Research Institute, Toronto, Ontario, Canada
- Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
| | - Elena K Grant
- Laboratory of Imaging Technology, Biochemistry and Biophysics Center, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
- Department of Cardiology, Children's National Medical Center, Washington, DC, USA
| | - Henry Chubb
- Division of Imaging Sciences and Biomedical Engineering, King's College London, UK
| | - Kawal Rhode
- Division of Imaging Sciences and Biomedical Engineering, King's College London, UK
| | - Graham A Wright
- Physical Sciences Platform and Schulich Heart Program, Sunnybrook Research Institute, Toronto, Ontario, Canada
- Medical Biophysics, University of Toronto, Toronto, Ontario, Canada
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Winkler SA, Picot PA, Thornton MM, Rutt BK. Direct SAR mapping by thermoacoustic imaging: A feasibility study. Magn Reson Med 2017; 78:1599-1606. [PMID: 27779779 PMCID: PMC5405009 DOI: 10.1002/mrm.26517] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 09/01/2016] [Accepted: 09/27/2016] [Indexed: 11/09/2022]
Abstract
PURPOSE To develop a new method capable of directly measuring specific absorption rate (SAR) deposited in tissue using the thermoacoustic signal induced by short radiofrequency (RF) pulse excitation. THEORY A detailed model based on the thermoacoustic wave generation and propagation is presented. METHODS We propose a new concept for direct measurement of SAR, to be used as a safety assessment/monitoring tool for MRI. The concept involves the use of short bursts of RF energy and the measurement of the resulting thermoacoustic excitation pattern by an array of ultrasound transducers, followed by image reconstruction to yield the 3D SAR distribution. We developed a simulation framework to model this thermoacoustic SAR mapping concept and verified the concept in vitro. RESULTS Simulations show good agreement between reconstructed and original SAR distributions with an error of 4.2, 7.2, and 8.4% of the mean SAR values in axial, sagittal, and coronal planes and support the feasibility of direct experimental mapping of SAR distributions in vivo. The in vitro experiments show good agreement with theory (r2 = 0.52). CONCLUSIONS A novel thermoacoustic method for in vivo mapping of local SAR patterns in MRI has been proposed and verified in simulation and in a phantom experiment. Magn Reson Med 78:1599-1606, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Simone A. Winkler
- Department of Radiology, Stanford University, Stanford, California, USA
| | | | | | - Brian K. Rutt
- Department of Radiology, Stanford University, Stanford, California, USA
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Venkateswaran M, Unal O, Hurley S, Samsonov A, Wang P, Fain SB, Kurpad KN. Modeling Endovascular MRI Coil Coupling With Transmit RF Excitation. IEEE Trans Biomed Eng 2016; 64:70-77. [PMID: 26960218 DOI: 10.1109/tbme.2016.2538279] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
OBJECTIVE To model inductive coupling of endovascular coils with transmit RF excitation for selecting coils for MRI-guided interventions. METHODS Independent and computationally efficient FEM models are developed for the endovascular coil, cable, transmit excitation, and imaging domain. Electromagnetic and circuit solvers are coupled to simulate net B1 + fields and induced currents and voltages. Our models are validated using the Bloch-Siegert B1 + mapping sequence for a series-tuned multimode coil, capable of tracking, wireless visualization, and high-resolution endovascular imaging. RESULTS Validation shows good agreement at 24-, 28-, and 34-μT background RF excitation within experimental limitations. Quantitative coil performance metrics agree with simulation. A parametric study demonstrates tradeoff in coil performance metrics when varying number of coil turns. Tracking, imaging, and wireless marker multimode coil features and their integration is demonstrated in a pig study. CONCLUSION Developed models for the multimode coil were successfully validated. Modeling for geometric optimization and coil selection serves as a precursor to time consuming and expensive experiments. Specific applications demonstrated include parametric optimization, coil selection for a cardiac intervention, and an animal imaging experiment. SIGNIFICANCE Our modular, adaptable, and computationally efficient modeling approach enables rapid comparison, selection, and optimization of inductively coupled coils for MRI-guided interventions.
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Etezadi-Amoli M, Stang P, Kerr A, Pauly J, Scott G. Controlling radiofrequency-induced currents in guidewires using parallel transmit. Magn Reson Med 2015; 74:1790-802. [PMID: 25521751 PMCID: PMC4470871 DOI: 10.1002/mrm.25543] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2014] [Revised: 10/31/2014] [Accepted: 11/02/2014] [Indexed: 11/09/2022]
Abstract
PURPOSE Elongated conductors, such as pacemaker leads, neurostimulator leads, and conductive guidewires used for interventional procedures can couple to the MRI radiofrequency (RF) transmit field, potentially causing dangerous tissue heating. The purpose of this study was to demonstrate the feasibility of using parallel transmit to control induced RF currents in elongated conductors, thereby reducing the RF heating hazard. METHODS Phantom experiments were performed on a four-channel parallel transmit system at 1.5T. Parallel transmit "null mode" excitations that induce minimal wire current were designed using coupling measurements derived from axial B1 (+) maps. The resulting current reduction performance was evaluated with B1 (+) maps, current sensor measurements, and fluoroptic temperature probe measurements. RESULTS Null mode excitations reduced the maximum coupling mode current by factors ranging from 2 to 80. For the straight wire experiment, a current null imposed at a single wire location was sufficient to reduce tip heating below detectable levels. For longer insertion lengths and a curved geometry, imposing current nulls at two wire locations resulted in more distributed current reduction along the wire length. CONCLUSION Parallel transmit can be used to create excitations that induce minimal RF current in elongated conductors, thereby decreasing the RF heating risk, while still allowing visualization of the surrounding volume.
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Affiliation(s)
- Maryam Etezadi-Amoli
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - Pascal Stang
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - Adam Kerr
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - John Pauly
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - Greig Scott
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA
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