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Zhu H, Zhang Q, Li R, Chen Y, Zhang G, Wang R, Lu M, Yan X. Detunable wireless resonator arrays for TMJ MRI: A comparative study. Magn Reson Imaging 2024; 111:84-89. [PMID: 38621550 DOI: 10.1016/j.mri.2024.04.016] [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: 03/04/2024] [Revised: 04/12/2024] [Accepted: 04/12/2024] [Indexed: 04/17/2024]
Abstract
Temporomandibular Joint Magnetic Resonance Imaging (TMJ MRI) is crucial for diagnosing temporomandibular disorders (TMDs). This study advances the use of inductively coupled wireless coils to enhance imaging quality in TMJ MRI. After investigating multiple wireless resonator configurations, including a 1-loop design with a loop diameter of 9 cm, a 2-loop design with each loop having a diameter of 7 cm, and a 3-loop design with each loop having a diameter of 5 cm, our findings indicate that the 3-loop configuration achieves the optimal signal-to-noise ratio (SNR), surpassing other wireless arrays. Bilateral deployment of wireless coils further amplifies SNR, enabling superior visualization of TMJ structures, particularly with the 3-loop design. This cost-effective and comfortable solution, featuring a detunable design, eliminates the need for system parameter adjustments. The study indicates broad adaptability across MRI platforms, enhancing TMJ imaging for routine clinical diagnostics of TMDs.
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Affiliation(s)
- Haoqin Zhu
- Sino Canada Health Institute Inc., Winnipeg, Manitoba, Canada.
| | - Qiang Zhang
- The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, Inner Mongolia 010010, China
| | - Rangsong Li
- Sino Canada Health Engineering Research Institute (Hefei) Ltd. Hefei, Anhui 230088, China
| | - Yuanyuan Chen
- Sino Canada Health Engineering Research Institute (Hefei) Ltd. Hefei, Anhui 230088, China
| | - Gong Zhang
- Hubei Key Laboratory of Intelligent Conveying Technology and Device, Hubei Polytechnic University, China
| | - Ruilin Wang
- College of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai, Shandong, China
| | - Ming Lu
- College of Nuclear Equipment and Nuclear Engineering, Yantai University, Yantai, Shandong, China
| | - Xinqiang Yan
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN 37232, USA; Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN 37232, USA.
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Zhu H, Lang ML, Yang Y, Martin M, Zhang G, Zhang Q, Chen Y, Yan X. Detunable wireless Litzcage coil for human head MRI at 1.5 T. NMR IN BIOMEDICINE 2024; 37:e5068. [PMID: 37964107 DOI: 10.1002/nbm.5068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 10/09/2023] [Accepted: 10/11/2023] [Indexed: 11/16/2023]
Abstract
Inductively coupled radiofrequency (RF) coils are an inexpensive and simple method to realize wireless RF coils in magnetic resonance imaging (MRI), which can significantly ease the MRI scan setup and improve patient comfort because they do not require bulky components such as cables, baluns, preamplifiers, and connectors. However, volume-type wireless coils are typically operated in transmit/receive mode because detuning such coils is much more challenging due to their complex structure and multiple resonant modes. Meanwhile, adding too many detuning circuits to a wireless coil would decrease the coil's quality factor, impair the signal-to-noise ratio, and increase the cost. In this work, we proposed, constructed, and tested a novel wireless volume coil based on the Litzcage design for 1.5-T head imaging. Being an inductively coupled coil, it has a much simpler structure, resulting in a lighter weight and less bulky design. Despite its simpler structure, it exhibits comparable imaging performance with a commercial receive array, providing an alternative to conventional wired coils with a high cost and complex structure. The unique figure-of-8 conductor pattern within the rungs ensures that the proposed wireless Litzcage can be efficiently detuned with minimal detuning circuits.
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Affiliation(s)
- Haoqin Zhu
- Sino Canada Health Institute Inc., Winnipeg, Manitoba, Canada
| | - Michael L Lang
- Sino Canada Health Institute Inc., Winnipeg, Manitoba, Canada
- Department of Physics, The University of Winnipeg, Winnipeg, Manitoba, Canada
| | - Yijin Yang
- Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, Tennessee, USA
| | - Melanie Martin
- Department of Physics, The University of Winnipeg, Winnipeg, Manitoba, Canada
| | - Gong Zhang
- Hubei Key Laboratory of Intelligent Conveying Technology and Device, Hubei Polytechnic University, Huangshi, China
| | - Qiang Zhang
- The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, China
| | - Yuanyuan Chen
- Sino Canada Health Engineering Research Institute (Hefei) Ltd., Hefei, Anhui, China
| | - Xinqiang Yan
- Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, Tennessee, USA
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA
- Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA
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Huang CFJ, Lin WL, Hwang SC, Yao C, Chang H, Chen YY, Kuo LW. A feasibility study of wireless inductively coupled surface coil for MR-guided high-intensity focused ultrasound ablation of rodents on clinical MRI systems. Sci Rep 2022; 12:21907. [PMID: 36536022 PMCID: PMC9763396 DOI: 10.1038/s41598-022-26452-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2022] [Accepted: 12/14/2022] [Indexed: 12/23/2022] Open
Abstract
Recently, to conduct preclinical imaging research on clinical MRI systems has become an attractive alternative to researchers due to its wide availability, cost, and translational application to clinical human studies when compared to dedicated small animal, high-field preclinical MRI. However, insufficient signal-to-noise ratio (SNR) significantly degrades the applicability of those applications which require high SNR, e.g. magnetic resonance guided high-intensity focused ultrasound (MRgHIFU) treatment. This study introduces a wireless inductively coupled surface (WICS) coil design used on a clinical 3 T MRI system for MRgHIFU ablation. To evaluate the SNR improvement and temperature accuracy of WICS coil, the ex vivo experiments were performed on the pork tenderloins (n = 7) and the hind legs of deceased Sprague-Dawley rats (n = 5). To demonstrate the feasibility, the in vivo experiments were performed on the hind leg of Sprague-Dawley rat (n = 1). For all experiments, temperature measurements were performed before and during HIFU ablation. Temperature curves with and without WICS coil were compared to evaluate the temperature precision in ex vivo experiments. The use of WICS coil improves the temperature accuracy from 0.85 to 0.14 °C, demonstrating the feasibility of performing small animal MRgHIFU experiments using clinical 3 T MRI system with WICS coil.
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Affiliation(s)
- Chien-Feng Judith Huang
- grid.19188.390000 0004 0546 0241Department of Biomedical Engineering, National Taiwan University, Taipei, 100233 Taiwan ,grid.59784.370000000406229172Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Miaoli, 35053 Taiwan
| | - Win-Li Lin
- grid.19188.390000 0004 0546 0241Department of Biomedical Engineering, National Taiwan University, Taipei, 100233 Taiwan ,grid.59784.370000000406229172Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Miaoli, 35053 Taiwan
| | - San-Chao Hwang
- MBInsight Technology Corporation, New Taipei City, 236658 Taiwan
| | - Ching Yao
- MBInsight Technology Corporation, New Taipei City, 236658 Taiwan
| | - Hsu Chang
- MBInsight Technology Corporation, New Taipei City, 236658 Taiwan
| | - Yung-Yaw Chen
- grid.19188.390000 0004 0546 0241Department of Electrical Engineering, National Taiwan University, Taipei, 100233 Taiwan
| | - Li-Wei Kuo
- grid.59784.370000000406229172Institute of Biomedical Engineering and Nanomedicine, National Health Research Institutes, Miaoli, 35053 Taiwan ,grid.19188.390000 0004 0546 0241Institute of Medical Device and Imaging, National Taiwan University, Taipei, 100233 Taiwan
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Gulyaev MV, Protopopov A, Pavlova OS, Anisimov NV, Pirogov YA. Design and first implementation of wireless square-shaped transmission line resonators in 1H MRI for small animal studies. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 339:107216. [PMID: 35413516 DOI: 10.1016/j.jmr.2022.107216] [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: 12/21/2021] [Revised: 03/25/2022] [Accepted: 04/02/2022] [Indexed: 06/14/2023]
Abstract
This work is dedicated to the development of a novel design for wireless transmission line resonators (TLRs). The TLRs are often considered as circular-shaped coils made up of two conductive circuits separated by a dielectric layer. We propose a square-shaped TLR design, wherein the coil has two square turns with two symmetrical gaps on each of the conductive layers, and the latter are rotated relative to each other by 90°. The calculation error of the resonant frequency of the square-shaped TLRs is no more than ∼3% of the measured value. The effectiveness of the square-shaped TLR design was evaluated in comparative 1H MRI studies to conventional wireless square loop of the same resonant frequency and with the same-sized inner square of the TLR. The Bruker birdcage was used as a transceiver and as inductively coupled with the wireless coils. We found that the performance of the square-shaped TLR and the square loop is comparable, but the B1+-field generated by the TLR has a wider distribution profile. It was reflected in rat brain studies, when some structures of rat head were not captured by the square loop. Comparative experiments with a standard circular-shaped TLR showed that a signal is predominantly concentrated inside the inner turn of the TLRs. The proposed TLR design can be a promising path to be explored, especially for scanning small objects of study, when the scan area is comparable to the size of the rigid lumped capacitors.
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Affiliation(s)
| | - Alex Protopopov
- P.N. Lebedev Physical Institute of the Russian Academy of Sciences, Moscow 119991, Russia
| | - Olga S Pavlova
- Lomonosov Moscow State University, Moscow 119991, Russia.
| | | | - Yury A Pirogov
- Lomonosov Moscow State University, Moscow 119991, Russia
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Tesfai AS, Vollmer A, Özen AC, Braig M, Semper-Hogg W, Altenburger MJ, Ludwig U, Bock M. Inductively Coupled Intraoral Flexible Coil for Increased Visibility of Dental Root Canals in Magnetic Resonance Imaging. Invest Radiol 2022; 57:163-170. [PMID: 34510099 DOI: 10.1097/rli.0000000000000826] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
OBJECTIVES Accurate visualization of dental root canals is vital for the correct diagnosis and subsequent treatment. This work assesses the improvement of a dedicated new coil for dental magnetic resonance imaging (MRI) in comparison to conventional ones in terms of signal-to-noise ratio (SNR) and visibility. MATERIALS AND METHODS A newly developed intraoral flexible coil was used to display dental roots with MRI, and it provides improved sensitivity with a loop design and size adjusted to a single tooth anatomy. Ex vivo and in vivo measurements were performed on a 3 T clinical MR system, and results were compared with conventional head and surface coil images. Additional comparison was performed with a modified fast spin echo sequence and a constructive interference in steady-state sequence. RESULTS Ex vivo, an SNR gain of 6.3 could be achieved with the intraoral flexible coil setup, and higher visibility down to 200 μm was possible, whereas the external loop coil is limited to 400 μm. In vivo measurements in a volunteer resulted in an SNR gain of up to 4.5 with an improved delineation of the root canals, especially for the branch tissue splitting of the mesial root canal into mesial-buccal and mesial-lingual. CONCLUSIONS In summary, we showed the feasibility of implementing a wireless coil approach with readily available dental practice materials for sealing and placement. Highly improved MRI scans can be acquired within clinically feasible scan times, and this might provide additional medical findings to supplement available x-ray images.
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Affiliation(s)
| | - Andreas Vollmer
- Department of Oral and Craniomaxillofacial Surgery, Center for Dental Medicine, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg
| | | | | | - Wiebke Semper-Hogg
- Department of Oral and Craniomaxillofacial Surgery, Center for Dental Medicine, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg
| | - Markus Jörg Altenburger
- Department of Operative Dentistry and Periodontology, Center for Dental Medicine, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany
| | - Ute Ludwig
- From the Department of Radiology, Medical Physics
| | - Michael Bock
- From the Department of Radiology, Medical Physics
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Artifact quantification of venous stents in the MRI environment: Differences between braided and laser-cut designs. Phys Med 2021; 88:1-8. [PMID: 34147868 DOI: 10.1016/j.ejmp.2021.06.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2021] [Revised: 05/19/2021] [Accepted: 06/04/2021] [Indexed: 02/06/2023] Open
Abstract
PURPOSE To quantify B0- and B1-induced imaging artifacts of braided venous stents and to compare the artifacts to a set of laser-cut stents used in venous interventions. METHODS Three prototypes of braided venous stents with different geometries were tested in vitro. B0 field distortion maps were measured via the frequency shift Δf using multi-echo imaging. B1 distortions were quantified using the double angle method. The relative amplitudes B1rel were calculated to compare the intraluminal alteration of B1. Measurements were repeated with the stents in three different orientations: parallel, diagonal and orthogonal to B0. RESULTS At 1.5 T, the braided stents induced a maximum frequency shift of Δfx<100Hz. Signal voids were limited to a distance of 2 mm to the stent walls at an echo time of 3 ms. No substantial difference in the B0 field distortions was seen between laser-cut and braided venous stents. B1rel maps showed strongly varying distortion patterns in the braided stents with the mean intraluminal B1rel ranging from 63±18% in prototype 1 to 98±38% in prototype 2. Compared to laser-cut stents the braided stents showed a 5 to 9 times higher coefficient of variation of the intraluminal B1rel. CONCLUSION Braided venous stent prototypes allow for MR imaging of the intraluminal area without substantial signal voids due to B0-induced artifacts. Whereas B1 is attenuated homogeneously in laser-cut stents, the B1 distortion in braided stents is more inhomogeneous and shows areas with enhanced amplitude. This could potentially be used in braided stent designs for intraluminal signal amplification.
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Park BS, Rajan SS, McCright B. Sensitivity and uniformity improvement of phased array MR images using inductive coupling and RF detuning circuits. MAGMA (NEW YORK, N.Y.) 2020; 33:725-733. [PMID: 31980963 DOI: 10.1007/s10334-020-00827-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Revised: 12/26/2019] [Accepted: 01/09/2020] [Indexed: 11/28/2022]
Abstract
OBJECTIVE To improve sensitivity and uniformity of MR images obtained using a phased array RF coil, an inductively coupled secondary resonator with RF detuning circuits at 300 MHz was designed. MATERIALS AND METHODS A secondary resonator having detuning circuits to turn off the resonator during the transmit mode was constructed. The secondary resonator was located at the opposite side of the four-channel phased array to improve sensitivity and uniformity of the acquired MR images. Numerical simulations along with phantom and in vivo experiments were conducted to evaluate the designed secondary resonator. RESULTS The numerical simulation results of |B1+| in a transmit mode showed that magnetic field uniformity would be decreased with a secondary resonator having no detuning circuits because of unwanted interferences between the transmit birdcage coil and the secondary resonator. The standard deviation (SD) of |B1+| was decreased 57% with a secondary resonator containing detuning circuits. The sensitivity and uniformity of |B1-| in the receive mode using a four-channel phased array were improved with the secondary resonator. Phantom experiments using a uniform saline phantom had 20% improvement of the mean signal intensity and 50% decrease in the SD with the secondary resonator. Mice with excess adipose tissue were imaged to demonstrate the utility of the secondary resonator. CONCLUSION The designed secondary resonator having detuning circuits improved sensitivity and uniformity of mouse MR images acquired using the four-channel phased array.
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Affiliation(s)
- Bu S Park
- Division of Cellular and Gene Therapies (DCGT)/OTAT/CBER, Food and Drug Administration, Silver Spring, MD, 20993-0002, USA.
| | - Sunder S Rajan
- Division of Biomedical Physics (DBP)/OSEL/CDRH, Food and Drug Administration, Silver Spring, MD, 20993-0002, USA
| | - Brent McCright
- Division of Cellular and Gene Therapies (DCGT)/OTAT/CBER, Food and Drug Administration, Silver Spring, MD, 20993-0002, USA
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Heidt T, Reiss S, Krafft AJ, Özen AC, Lottner T, Hehrlein C, Galmbacher R, Kayser G, Hilgendorf I, Stachon P, Wolf D, Zirlik A, Düring K, Zehender M, Meckel S, von Elverfeldt D, Bode C, Bock M, von Zur Mühlen C. Real-time magnetic resonance imaging - guided coronary intervention in a porcine model. Sci Rep 2019; 9:8663. [PMID: 31209241 PMCID: PMC6572773 DOI: 10.1038/s41598-019-45154-7] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2018] [Accepted: 06/03/2019] [Indexed: 11/28/2022] Open
Abstract
X-ray fluoroscopy is the gold standard for coronary diagnostics and intervention. Magnetic resonance imaging is a radiation-free alternative to x-ray with excellent soft tissue contrast in arbitrary slice orientation. Here, we assessed real-time MRI-guided coronary interventions from femoral access using newly designed MRI technologies. Six Goettingen minipigs were used to investigate coronary intervention using real-time MRI. Catheters were custom-designed and equipped with an active receive tip-coil to improve visibility and navigation capabilities. Using modified standard clinical 5 F catheters, intubation of the left coronary ostium was successful in all animals. For the purpose of MR-guided coronary interventions, a custom-designed 8 F catheter was used. In spite of the large catheter size, and therefore limited steerability, intubation of the left coronary ostium was successful in 3 of 6 animals within seconds. Thereafter, real-time guided implantation of a non-metallic vascular scaffold into coronary arteries was possible. This study demonstrates that real-time MRI-guided coronary catheterization and intervention via femoral access is possible without the use of any contrast agents or radiation, including placement of non-metallic vascular scaffolds into coronary arteries. Further development, especially in catheter and guidewire technology, will be required to drive forward routine MR-guided coronary interventions as an alternative to x-ray fluoroscopy.
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Affiliation(s)
- Timo Heidt
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany.
| | - Simon Reiss
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Axel J Krafft
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Ali Caglar Özen
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Thomas Lottner
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Christoph Hehrlein
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Roland Galmbacher
- Department of Experimental Anesthesiology, University Hospital Heidelberg, Heidelberg, Germany
| | - Gian Kayser
- Department of Pathology, Institute of Surgical Pathology, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Ingo Hilgendorf
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Peter Stachon
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Dennis Wolf
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Andreas Zirlik
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | | | - Manfred Zehender
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Stephan Meckel
- Department of Neuroradiology, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Dominik von Elverfeldt
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Christoph Bode
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
| | - Michael Bock
- Department of Radiology, Medical Physics, University Medical Center Freiburg, Faculty of Medicine, Freiburg, Germany
| | - Constantin von Zur Mühlen
- Cardiology and Angiology I, Heart Center Freiburg University and Faculty of Medicine, Freiburg, Germany
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Abstract
Diagnostic and interventional cardiac catheterization is routinely used in the diagnosis and treatment of congenital heart disease. There are well-established concerns regarding the risk of radiation exposure to patients and staff, particularly in children given the cumulative effects of repeat exposure. Magnetic resonance imaging (MRI) offers the advantage of being able to provide better soft tissue visualization, tissue characterization, and quantification of ventricular volumes and vascular flow. Initial work using MRI catheterization employed fusion of x-ray and MRI techniques, with x-ray fluoroscopy to guide catheter placement and subsequent MRI assessment for anatomical and hemodynamic assessment. Image overlay of 3D previously acquired MRI datasets with live fluoroscopic imaging has also been used to guide catheter procedures.Hybrid x-ray and MRI-guided catheterization paved the way for clinical application and validation of this technique in the assessment of pulmonary vascular resistance and pharmacological stress studies. Purely MRI-guided catheterization also proved possible with passive catheter tracking. First-in-man MRI-guided cardiac catheter interventions were possible due to the development of MRI-compatible guidewires, but halted due to guidewire limitations.More recent developments in passive and active catheter tracking have led to improved visualization of catheters for MRI-guided catheterization. Improvements in hardware and software have also increased image quality and scanning times with better interactive tools for the operator in the MRI catheter suite to navigate through the anatomy as required in real time. This has expanded to MRI-guided electrophysiology studies and radiofrequency ablation in humans. Animal studies show promise for the utility of MRI-guided interventional catheterization. Ongoing investment and development of MRI-compatible guidewires will pave the way for MRI-guided diagnostic and interventional catheterization coming into the mainstream.
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Kamberger R, Göbel-Guéniot K, Gerlach J, Gruschke OG, Hennig J, LeVan P, Haas C, Korvink JG. Improved method for MR microscopy of brain tissue cultured with the interface method combined with Lenz lenses. Magn Reson Imaging 2018; 52:24-32. [PMID: 29857037 DOI: 10.1016/j.mri.2018.05.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 05/21/2018] [Accepted: 05/21/2018] [Indexed: 12/17/2022]
Abstract
MR in microscopy can non-invasively image the morphology of living tissue, which is of particular interest in studying the mammalian brain. Many studies use live animals for basic research on brain functions, disease pathogenesis, and drug development. However, in vitro systems are on the rise, due to advantages such as the absence of a blood-brain barrier, predictable pharmacokinetics, and reduced ethical restrictions. Hence, they present an inexpensive and adequate technique to answer scientific questions and to perform drug screenings. Some publications report the use of acute brain slices for MR microscopy studies, but these only permit single measurements over several hours. Repetitive MR measurements in longitudinal studies demand an MR-compatible setup which allows cultivation for several days or weeks, and hence properly functioning in vitro systems. Organotypic hippocampal slice cultures (OHSC) are a well-established and robust in vitro system which still exhibits most histological hallmarks of the hippocampal network in vivo. An MR compatible incubation platform is introduced in which OHSC are cultivated according to the interface method following Stoppini et al. In this cultivation method a tissue slice is placed onto a membrane with nutrition medium underneath and a gas atmosphere above, where the air-tissue interface perpendicular to the B0 field induces strong artefacts. We introduce a handling protocol that suppresses these artefacts and increases signal quality significantly to acquire high resolution images of tissue slices. An additional challenge is the lack of available of MR microscopy equipment suitable for small animal scanners. A Lenz lens with an attached capacitor can dramatically increase the SNR in these cases, and wirelessly bring the detection system in close proximity to the sample without compromising the OHSC system through the introduction of wired detectors. The resultant signal gain is demonstrated by imaging a PFA-fixed brain slice with a 72 mm diameter volume coil without a Lenz lens, and with a broadband and a self-resonant Lenz lens. In our setting, the self-resonant Lenz lens increases the SNR 10-fold over using the volume coil only.
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Affiliation(s)
- R Kamberger
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany
| | - K Göbel-Guéniot
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany; Medical Physics, Department of Radiology, Medical Center - University of Freiburg, Germany
| | - J Gerlach
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany; Experimental Epilepsy Laboratory, Department of Neurosurgery, Medical Center - University of Freiburg, Germany
| | - O G Gruschke
- Institute of Microstructure Technology, Karlsruhe Institute of Technology, Germany
| | - J Hennig
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany; Medical Physics, Department of Radiology, Medical Center - University of Freiburg, Germany
| | - P LeVan
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany; Medical Physics, Department of Radiology, Medical Center - University of Freiburg, Germany
| | - C Haas
- BrainLinks-BrainTools Cluster of Excellence, University of Freiburg, Germany; Experimental Epilepsy Laboratory, Department of Neurosurgery, Medical Center - University of Freiburg, Germany
| | - J G Korvink
- Institute of Microstructure Technology, Karlsruhe Institute of Technology, Germany.
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Jouda M, Kamberger R, Leupold J, Spengler N, Hennig J, Gruschke O, Korvink JG. A comparison of Lenz lenses and LC resonators for NMR signal enhancement. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2017; 47B:e21357. [PMID: 29541005 PMCID: PMC5839471 DOI: 10.1002/cmr.b.21357] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 09/11/2017] [Accepted: 10/26/2017] [Indexed: 06/09/2023]
Abstract
High signal-to-noise ratio (SNR) of the NMR signal has always been a key target that drives massive research effort in many fields. Among several parameters, a high filling factor of the MR coil has proven to boost the SNR. In case of small-volume samples, a high filling factor and thus a high SNR can be achieved through miniaturizing the MR coil. However, under certain circumstances, this can be impractical. In this paper, we present an extensive theoretical and experimental investigation of the inductively coupled LC resonator and the magnetic Lenz lens as two candidate approaches that can enhance the SNR in such circumstances. The results demonstrate that the narrow-band LC resonator is superior in terms of SNR, while the non-tuned nature of the Lenz lens makes it preferable in broadband applications.
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Affiliation(s)
- Mazin Jouda
- Karlsruhe Institute of Technology‐KITInstitute of Microstructure Technology‐IMTEggenstein‐LeopoldshafenGermany
| | - Robert Kamberger
- BrainLinks‐BrainTools Cluster of ExcellenceInstitute of Microsystems Technology‐IMTEKUniversity of FreiburgFreiburgGermany
| | - Jochen Leupold
- Department of RadiologyMedical PhysicsMedical Center ‐ University of FreiburgFaculty of MedicineUniversity of FreiburgFreiburgGermany
| | | | - Jürgen Hennig
- Department of RadiologyMedical PhysicsMedical Center ‐ University of FreiburgFaculty of MedicineUniversity of FreiburgFreiburgGermany
| | | | - Jan G. Korvink
- Karlsruhe Institute of Technology‐KITInstitute of Microstructure Technology‐IMTEggenstein‐LeopoldshafenGermany
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12
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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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Abstract
Interventional cardiovascular magnetic resonance (iCMR) promises to enable radiation-free catheterization procedures and to enhance contemporary image guidance for structural heart and electrophysiological interventions. However, clinical translation of exciting pre-clinical interventions has been limited by availability of devices that are safe to use in the magnetic resonance (MR) environment. We discuss challenges and solutions for clinical translation, including MR-conditional and MR-safe device design, and how to configure an interventional suite. We review the recent advances that have already enabled diagnostic MR right heart catheterization and simple electrophysiologic ablation to be performed in humans and explore future clinical applications.
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14
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Sarioglu B, Tumer M, Cindemir U, Camli B, Dundar G, Ozturk C, Yalcinkaya AD. An optically powered CMOS tracking system for 3 T magnetic resonance environment. IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS 2015; 9:12-20. [PMID: 24893369 DOI: 10.1109/tbcas.2014.2311474] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
In this work, a fully optical Complementary Metal Oxide Semiconductor (CMOS) based catheter tracking system designed for 3 T Magnetic Resonance Imaging (MRI) environment is presented. The system aims to solve the Radio Frequency (RF) induced heating problem present in conventional wired catheter tracking systems used in MRI. It is based on an integrated circuit, consisting of a receiver and an optical power supply unit. The optical power supply unit includes a single on-chip photodiode and a DC-DC converter that boosts the low photodiode voltage output to voltages greater than 1.5 V. Through an optically driven switch, the accumulated charge on an a storage capacitor is transferred to the rest of the system. This operation is novel in the way that it is fully optical and the switch control is done through modulation of the applied light. An on-chip local oscillator signal for the receiver is avoided by application of an RF signal that is generated by the MRI machine at the receiving period. The signals received by a micro-coil antenna are processed by the on-chip direct conversion receiver. The processed signal is then transferred, also optically, to the outside world for tracking purposes. The frequency encoding method is used for MRI tracking. Operation with various levels of external optical power does not generate noticeble temperature increase in the system. The overall system is successfully tested in a 3 T MRI machine to demonstrate its full operation.
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15
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Tümer M, Sarioglu B, Mutlu S, Ulgen Y, Yalcinkaya A, Ozturk C. Using a low-amplitude RF pulse at echo time (LARFET) for device localization in MRI. Med Biol Eng Comput 2014; 52:885-94. [PMID: 25173518 DOI: 10.1007/s11517-014-1184-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 08/13/2014] [Indexed: 11/28/2022]
Abstract
We describe a new method for frequency down-conversion of MR signals acquired with the radio-frequency projections method for device localization. A low-amplitude, off-center RF pulse applied simultaneously with the echo signal is utilized as the reference for frequency down-conversion. Because of the low-amplitude and large offset from the Larmor frequency, the RF pulse minimally interfered with magnetic resonance of protons. We conducted an experiment with the coil placed at different positions to verify this concept. The down-converted signal was transformed into optical signal and transmitted via fiber-optic cable to a receiver unit placed outside the scanner room. The position of the coil could then be determined by the frequency analysis of this down-converted signal and superimposed on previously acquired MR images for comparison. Because of minimal positional errors (≤ 0.8 mm), this new device localization method may be adequate for most interventional MRI applications.
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Affiliation(s)
- Murat Tümer
- Institute of Biomedical Engineering, Boğaziçi University, Istanbul, Turkey,
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16
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Ooi MB, Aksoy M, Maclaren J, Watkins RD, Bammer R. Prospective motion correction using inductively coupled wireless RF coils. Magn Reson Med 2013; 70:639-47. [PMID: 23813444 DOI: 10.1002/mrm.24845] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 05/22/2013] [Accepted: 05/24/2013] [Indexed: 11/06/2022]
Abstract
PURPOSE A novel prospective motion correction technique for brain MRI is presented that uses miniature wireless radio-frequency coils, or "wireless markers," for position tracking. METHODS Each marker is free of traditional cable connections to the scanner. Instead, its signal is wirelessly linked to the MR receiver via inductive coupling with the head coil. Real-time tracking of rigid head motion is performed using a pair of glasses integrated with three wireless markers. A tracking pulse-sequence, combined with knowledge of the markers' unique geometrical arrangement, is used to measure their positions. Tracking data from the glasses is then used to prospectively update the orientation and position of the image-volume so that it follows the motion of the head. RESULTS Wireless-marker position measurements were comparable to measurements using traditional wired radio-frequency tracking coils, with the standard deviation of the difference < 0.01 mm over the range of positions measured inside the head coil. Wireless-marker safety was verified with B1 maps and temperature measurements. Prospective motion correction was demonstrated in a 2D spin-echo scan while the subject performed a series of deliberate head rotations. CONCLUSION Prospective motion correction using wireless markers enables high quality images to be acquired even during bulk motions. Wireless markers are small, avoid radio-frequency safety risks from electrical cables, are not hampered by mechanical connections to the scanner, and require minimal setup times. These advantages may help to facilitate adoption in the clinic.
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Affiliation(s)
- Melvyn B Ooi
- Department of Radiology, Stanford University, Stanford, California, USA
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17
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Celik H, Mahcicek DI, Senel OK, Wright GA, Atalar E. Tracking the position and rotational orientation of a catheter using a transmit array system. IEEE TRANSACTIONS ON MEDICAL IMAGING 2013; 32:809-817. [PMID: 23412592 DOI: 10.1109/tmi.2013.2247047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A new method for detecting the rotational orientation and tracking the position of an inductively coupled radio frequency (ICRF) coil using a transmit array system is proposed. The method employs a conventional body birdcage coil, but the quadrature hybrid is eliminated so that the two excitation channels can be used separately. The transmit array system provides RF excitations such that the body birdcage coil creates linearly polarized and changing RF pulses instead of a conventional rotational forward-polarized excitation. The receive coils and their operations are not modified. Inductively coupled RF coils are constructed on catheters for detecting rotational orientation and for tracking purposes. Signals from the anatomy and from tissue close to the ICRF coil are different due to the new RF excitation scheme: the ICRF coil can be separated from the anatomy in real time, and after doing so, a color-coded image is reconstructed. More importantly, this novel method enables a real-time calculation of the absolute rotational orientation of an ICRF coil constructed on a catheter. Modified FLASH and TrueFISP sequences are used for the experiments. The acquired images from this technique show the feasibility of different applications, such as catheter tracking. Furthermore, applications where knowledge of the rotational orientation of the catheter is important, such as magnetic resonance-guided endoluminal-focused ultrasound, RF ablation, side-looking optical imaging, and catheters with side ports for needles, become feasible with this method.
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Affiliation(s)
- Haydar Celik
- Electrical and Electronics Engineering Department, Bilkent University, TR-06800 Ankara, Turkey.
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18
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Qian C, Zabow G, Koretsky A. Engineering novel detectors and sensors for MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2013; 229:67-74. [PMID: 23245489 PMCID: PMC4169702 DOI: 10.1016/j.jmr.2012.11.012] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/2012] [Revised: 11/07/2012] [Accepted: 11/08/2012] [Indexed: 06/01/2023]
Abstract
Increasing detection sensitivity and image contrast have always been major topics of research in MRI. In this perspective, we summarize two engineering approaches to make detectors and sensors that have potential to extend the capability of MRI. The first approach is to integrate miniaturized detectors with a wireless powered parametric amplifier to enhance the detection sensitivity of remotely coupled detectors. The second approach is to microfabricate contrast agents with encoded multispectral frequency shifts, whose properties can be specified and fine-tuned by geometry. These two complementary approaches will benefit from the rapid development in nanotechnology and microfabrication which should enable new opportunities for MRI.
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Affiliation(s)
- Chunqi Qian
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892
| | - Gary Zabow
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892
- Electromagnetics Division, National Institute of Standards and Technology, Boulder, CO, 80305
| | - Alan Koretsky
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, 20892
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19
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Takeda K. Microcoils and microsamples in solid-state NMR. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2012; 47-48:1-9. [PMID: 23083521 DOI: 10.1016/j.ssnmr.2012.09.002] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2012] [Revised: 09/13/2012] [Accepted: 09/14/2012] [Indexed: 06/01/2023]
Abstract
Recent reports on microcoils are reviewed. The first part of the review includes a discussion of how the geometries of the sample and coil affect the NMR signal intensity. In addition to derivation of the well-known result that the signal intensity increases as the coil size decreases, the prediction that dilution of a small sample with magnetically inert matter leads to better sensitivity if a tiny coil is not available is given. The second part of the review focuses on the issues specific to solid-state NMR. They include realization of magic-angle spinning (MAS) using a microcoil and harnessing of such strong pulses that are feasible only with a microcoil. Two strategies for microcoil MAS, the piggyback method and magic-angle coil spinning (MACS), are reviewed. In addition, MAS of flat, disk-shaped samples is discussed in the context of solid-state NMR of small-volume samples. Strong RF irradiation, which has been exploited in wide-line spectral excitation, multiple-quantum MAS (MQMAS), and dipolar decoupling experiments, has been accompanied by new challenges regarding the Bloch-Siegert effect, the minimum time resolution of the spectrometer, and the time scale of pulse transient effects. For a possible solution to the latter problem, recent reports on active compensation of pulse transients are described.
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Affiliation(s)
- Kazuyuki Takeda
- Division of Chemistry, Graduate School of Science, Kyoto University, 606-8502 Kyoto, Japan.
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20
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In vitro stent lumen visualisation of various common and newly developed femoral artery stents using MR angiography at 1.5 and 3 tesla. Eur Radiol 2012; 23:588-95. [PMID: 22898936 DOI: 10.1007/s00330-012-2625-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Revised: 07/18/2012] [Accepted: 07/18/2012] [Indexed: 10/28/2022]
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21
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Qian C, Murphy-Boesch J, Dodd S, Koretsky A. Sensitivity enhancement of remotely coupled NMR detectors using wirelessly powered parametric amplification. Magn Reson Med 2012; 68:989-96. [PMID: 22246567 DOI: 10.1002/mrm.23274] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2011] [Revised: 10/02/2011] [Accepted: 10/05/2011] [Indexed: 11/06/2022]
Abstract
A completely wireless detection coil with an integrated parametric amplifier has been constructed to provide local amplification and transmission of MR signals. The sample coil is one element of a parametric amplifier using a zero-bias diode that mixes the weak MR signal with a strong pump signal that is obtained from an inductively coupled external loop. The NMR sample coil develops current gain via reduction in the effective coil resistance. Higher gain can be obtained by adjusting the level of the pumping power closer to the oscillation threshold, but the gain is ultimately constrained by the bandwidth requirement of MRI experiments. A feasibility study here shows that on a NaCl/D(2) O phantom, (23) Na signals with 20 dB of gain can be readily obtained with a concomitant bandwidth of 144 kHz. This gain is high enough that the integrated coil with parametric amplifier, which is coupled inductively to external loops, can provide sensitivity approaching that of direct wire connection.
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Affiliation(s)
- Chunqi Qian
- Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorder and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
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22
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Saeed M, Hetts SW, English J, Wilson M. MR fluoroscopy in vascular and cardiac interventions (review). Int J Cardiovasc Imaging 2012; 28:117-37. [PMID: 21359519 PMCID: PMC3275732 DOI: 10.1007/s10554-010-9774-1] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/01/2010] [Accepted: 12/13/2010] [Indexed: 12/22/2022]
Abstract
Vascular and cardiac disease remains a leading cause of morbidity and mortality in developed and emerging countries. Vascular and cardiac interventions require extensive fluoroscopic guidance to navigate endovascular catheters. X-ray fluoroscopy is considered the current modality for real time imaging. It provides excellent spatial and temporal resolution, but is limited by exposure of patients and staff to ionizing radiation, poor soft tissue characterization and lack of quantitative physiologic information. MR fluoroscopy has been introduced with substantial progress during the last decade. Clinical and experimental studies performed under MR fluoroscopy have indicated the suitability of this modality for: delivery of ASD closure, aortic valves, and endovascular stents (aortic, carotid, iliac, renal arteries, inferior vena cava). It aids in performing ablation, creation of hepatic shunts and local delivery of therapies. Development of more MR compatible equipment and devices will widen the applications of MR-guided procedures. At post-intervention, MR imaging aids in assessing the efficacy of therapies, success of interventions. It also provides information on vascular flow and cardiac morphology, function, perfusion and viability. MR fluoroscopy has the potential to form the basis for minimally invasive image-guided surgeries that offer improved patient management and cost effectiveness.
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Affiliation(s)
- Maythem Saeed
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA 94107-1701, USA.
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23
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Quick HH. Interventional MRI in the cardiovascular system. Methods Mol Biol 2011; 771:421-38. [PMID: 21874491 DOI: 10.1007/978-1-61779-219-9_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/19/2023]
Abstract
Endovascular stent-graft placement for thoracic aortic disease such as aortic dissection or aortic aneurysms is usually performed under conventional X-ray guidance. The experimental concept of using magnetic resonance imaging (MRI) for image-based guidance of vascular instruments for this specific intervention potentially offers a number of features that - aside from not using ionizing radiation - may provide added diagnostic value to the interventional therapy. It allows not only pre-interventional evaluation and detailed anatomic diagnosis but also permits immediate post-interventional, anatomical, and functional delineation of procedure success that may serve as a baseline for future comparison during follow-up.
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Affiliation(s)
- Harald H Quick
- Institute of Medical Physics, Friedrich-Alexander-University Erlangen-Nürnberg, 91052 Erlangen, Germany.
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24
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Celik H, Atalar E. Reverse polarized inductive coupling to transmit and receive radiofrequency coil arrays. Magn Reson Med 2011; 67:446-56. [PMID: 21656566 DOI: 10.1002/mrm.23030] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Revised: 04/25/2011] [Accepted: 05/05/2011] [Indexed: 11/07/2022]
Abstract
In this study, the reverse polarization method is implemented using transmit and receive arrays to improve the visibility of the interventional devices. Linearly polarized signal sources--inductively and receptively coupled radiofrequency coils--are used in the experimental setups to demonstrate the ability of the method to separate these sources from a forward polarized anatomy signal. Two different applications of the reverse polarization method are presented here: (a) catheter tracking and (b) fiducial marker visualization, in both of which transmit and receive arrays are used. The performance of the reverse polarization method was further tested with phantom and volunteer studies, and the results proved the feasibility of this method with transmit and receive arrays.
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Affiliation(s)
- Haydar Celik
- National Research Center for Magnetic Resonance (UMRAM), Bilkent University, Ankara, Turkey
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25
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Kraemer NA, Immel E, Donker HCW, Melzer A, Ocklenburg C, Guenther RW, Buecker A, Krombach GA, Spuentrup E. Evaluation of an active vena cava filter for MR imaging in a swine model. Radiology 2010; 258:446-54. [PMID: 21079200 DOI: 10.1148/radiol.10092487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To evaluate the feasibility of magnetic resonance (MR) imaging-guided placement of an active vena cava filter (AVCF) in a swine model, the effectiveness of the system in filtering thrombi, and the detection of thrombi with MR imaging. MATERIALS AND METHODS This study was approved by the government committee on animal investigations. An AVCF tuned to the Larmor frequency of a 1.5-T MR unit was placed in the inferior vena cava (IVC) of seven pigs under real-time MR imaging guidance. Steady-state free precession sequences with four different flip angles (90°, 40°, 25°, and 15°), T1-weighted turbo spin-echo sequences with two flip angles (90° and 15°), and black-blood proton-density-weighted sequences with a flip angle of 90° were performed before and after filter placement. In six cases, extracorporeally produced thrombi were injected through the femoral access to test filter function. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed before and after filter deployment and compared by using the signed-rank test. RESULTS All AVCFs were successfully deployed. Significant differences (P < .05) in the SNR and CNR of the IVC were found before and after AVCF placement and between sequences with different flip angles. Intravenous thrombi were caught in all cases and clearly depicted with MR imaging. On black-blood proton-density-weighted images, high-signal-intensity thrombi inside the filter were clearly detectable without any overlaying artifacts. CONCLUSION MR imaging-guided deployment and monitoring of an AVCF is feasible. The AVCF enhances the SNR and CNR, resulting in clear depiction of thrombi inside the filter without the need for contrast material. Design modifications for improved intracaval fixation and retrieval of the prototype AVCF will be required.
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Affiliation(s)
- Nils A Kraemer
- Department of Diagnostic Radiology and Institute for Medical Statistics, University Hospital, RWTH Aachen University, Pauwelsstrasse 30, 52075 Aachen, Germany.
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26
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Abstract
Catheter ablation is a first-line treatment for many cardiac arrhythmias and is generally performed under X-ray fluoroscopy guidance. However, current techniques for ablating complex arrhythmias such as atrial fibrillation and ventricular tachycardia are associated with sub-optimal success rates and prolonged radiation exposure. Pre-procedure 3-D magnetic resonance imaging (MRI) has improved understanding of the anatomic basis of complex arrhythmias and is being used for planning and guidance of ablation procedures. A particular strength of MRI compared to other imaging modalities is the ability to visualize ablation lesions. Post-procedure MRI is now being applied to assess ablation lesion location and permanence with the goal of identifying factors leading to procedure success and failure. In the future, intra-procedure real-time MRI, together with the ability to image complex 3-D arrhythmogenic anatomy and target additional ablation to regions of incomplete lesion formation, may allow for more successful treatment of even complex arrhythmias without exposure to ionizing radiation. Development of clinical grade MRI-compatible electrophysiology devices is required to transition intra-procedure MRI from preclinical studies to more routine use in patients.
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27
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Gilbert G, Soulez G, Beaudoin G. Improved in-stent lumen visualization using intravascular MRI and a balanced steady-state free-precession sequence. Acad Radiol 2009; 16:1466-74. [PMID: 19836269 DOI: 10.1016/j.acra.2009.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2009] [Revised: 07/01/2009] [Accepted: 07/06/2009] [Indexed: 11/26/2022]
Abstract
RATIONALE AND OBJECTIVES To investigate the ability of an intravascular magnetic resonance (MR) loopless antenna to reduce the radiofrequency shielding of a vascular stent during signal reception as a way to improve the visualization of the in-stent lumen. METHODS AND MATERIALS Using a balanced steady-state free-precession (bSSFP) sequence and a dedicated vascular phantom, the signal-to-noise ratio (SNR) inside the lumen of a stent is evaluated as a function of the nominal flip angle and compared with the results obtained for a reference vessel without a stent. All experiments are performed using successively an intravascular loopless antenna and surface arrays coils. Using an optimized protocol, in vitro in-stent restenosis visualization and quantification experiments are performed to evaluate the validity of an approach using an intravascular antenna and cross-sectional images to depict a vascular lesion inside a stent. RESULTS The use of a loopless antenna effectively eliminates the radiofrequency shielding effect of the stent during signal reception. Furthermore, using a bSSFP sequence with a carefully chosen nominal flip angle, an equally good blood SNR can be obtained inside and outside the stent. Results of in vitro in-stent restenosis quantification measurements using the proposed method illustrate the benefits arising from the use of the intravascular antenna. CONCLUSION In the perspective of MR-guided vascular interventions, the presented results illustrate that the use of an intravascular antenna can significantly facilitate imaging inside a vascular stent. Potential applications include the monitoring of stent deployment as well as visualization and quantification of in-stent restenosis during an intervention.
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28
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Kolandaivelu A, Lardo AC, Halperin HR. Cardiovascular magnetic resonance guided electrophysiology studies. J Cardiovasc Magn Reson 2009; 11:21. [PMID: 19580654 PMCID: PMC2719626 DOI: 10.1186/1532-429x-11-21] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Accepted: 07/06/2009] [Indexed: 11/10/2022] Open
Abstract
Catheter ablation is a first line treatment for many cardiac arrhythmias and is generally performed under x-ray fluoroscopy guidance. However, current techniques for ablating complex arrhythmias such as atrial fibrillation and ventricular tachycardia are associated with suboptimal success rates and prolonged radiation exposure. Pre-procedure 3D CMR has improved understanding of the anatomic basis of complex arrhythmias and is being used for planning and guidance of ablation procedures. A particular strength of CMR compared to other imaging modalities is the ability to visualize ablation lesions. Post-procedure CMR is now being applied to assess ablation lesion location and permanence with the goal of indentifying factors leading to procedure success and failure. In the future, intra-procedure real-time CMR, together with the ability to image complex 3-D arrhythmogenic anatomy and target additional ablation to regions of incomplete lesion formation, may allow for more successful treatment of even complex arrhythmias without exposure to ionizing radiation. Development of clinical grade CMR compatible electrophysiology devices is required to transition intra-procedure CMR from pre-clinical studies to more routine use in patients.
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Affiliation(s)
| | - Albert C Lardo
- Johns Hopkins Hospital, Division of Cardiology, Baltimore, MD 21205, USA
| | - Henry R Halperin
- Johns Hopkins Hospital, Division of Cardiology, Baltimore, MD 21205, USA
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29
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Ciocan R, Lenkinski RE, Bernstein J, Bancu M, Marquis R, Ivanishev A, Kourtelidis F, Matsui A, Borenstein J, Frangioni JV. MRI contrast using solid-state, B1-distorting, microelectromechanical systems (MEMS) microresonant devices (MRDs). Magn Reson Med 2009; 61:860-6. [PMID: 19189289 DOI: 10.1002/mrm.21906] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Presently, signal generation in MRI depends on the concentration and relaxivity of protons or other MR-active nuclei, and contrast depends on local differences in signal. In this proof-of-principle study, we explore the use of nonchemical, solid-state devices for generating detectable signal and/or contrast in vitro and in vivo. We introduce the concept of microresonant devices (MRDs), which are micron-sized resonators fabricated using microelectromechanical systems (MEMS) technology. Fifteen-micrometer (15-microm)-thick, coil MRDs were designed to resonate at the 3T Larmor frequency of protons (127.7 MHz) and were fabricated using tantalum (Ta) oxide thin-film capacitors and copper-plated spiral inductors. The performance of MRDs having final diameters of 300, 500, and 1000 microm were characterized in saline using a radio frequency (RF) scanning microscope and a clinical 3T MR scanner. The measured B(1) fields of 300 microm to 1000 microm MRDs ranged from 3.25 microT to 3.98 microT, and their quality factors (Q) ranged from 3.9 to 7.2. When implanted subcutaneously in the flank of a mouse, only MRDs tuned to the resonant frequency of protons generated a measurable in vivo B(1) field. This study lays the foundation for a new class of solid-state contrast agents for MRI.
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Affiliation(s)
- Razvan Ciocan
- Division of Hematology/Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA
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30
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Ratnayaka K, Faranesh AZ, Guttman MA, Kocaturk O, Saikus CE, Lederman RJ. Interventional cardiovascular magnetic resonance: still tantalizing. J Cardiovasc Magn Reson 2008; 10:62. [PMID: 19114017 PMCID: PMC2637847 DOI: 10.1186/1532-429x-10-62] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Accepted: 12/29/2008] [Indexed: 12/30/2022] Open
Abstract
The often touted advantages of MR guidance remain largely unrealized for cardiovascular interventional procedures in patients. Many procedures have been simulated in animal models. We argue these opportunities for clinical interventional MR will be met in the near future. This paper reviews technical and clinical considerations and offers advice on how to implement a clinical-grade interventional cardiovascular MR (iCMR) laboratory. We caution that this reflects our personal view of the "state of the art."
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Affiliation(s)
- Kanishka Ratnayaka
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
- Cardiology Division, Children's National Medical Center, Washington, DC, USA
| | - Anthony Z Faranesh
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Michael A Guttman
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Ozgur Kocaturk
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Christina E Saikus
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Robert J Lederman
- Translational Medicine Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
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Bock M, Wacker FK. MR-guided intravascular interventions: techniques and applications. J Magn Reson Imaging 2008; 27:326-38. [PMID: 18219686 DOI: 10.1002/jmri.21271] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Magnetic resonance imaging (MRI) offers several advantages over other imaging modalities that make it an attractive imaging tool for diagnostic and therapeutic procedures. This tremendous potential of MRI has provided the rationale for increased attention toward MR-guided endovascular interventions. MR guidance has been used recently to navigate endovascular catheters and deliver stents, vena cava filters, embolization materials, and septum closure devices. However, its potential goes beyond just copying existing procedures toward the development of new minimally invasive techniques that cannot be performed with conventional guiding techniques. Because of technical limitations and safety issues associated with some of the currently available devices, a limited number of clinical studies have been performed so far. The overall success for this developing field requires considerable interdisciplinary research within both the interventional and the MR community. Only through a combined effort can this complex technology find its way into clinical practice. This review discusses the hardware and software improvements that have helped to advance endovascular interventions under MR imaging guidance from a pure research tool to become a clinical reality. In addition, technical and safety issues specific to endovascular MR image guidance will be described and practical applications will be shown that take advantage of the benefits of MR for endovascular interventions.
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Affiliation(s)
- Michael Bock
- Deutsches Krebsforschungszentrum, Department of Medical Physics in Radiology (E020), Heidelberg, Germany
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Raman VK, Lederman RJ. Interventional cardiovascular magnetic resonance imaging. Trends Cardiovasc Med 2007; 17:196-202. [PMID: 17662914 PMCID: PMC2291392 DOI: 10.1016/j.tcm.2007.05.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Revised: 05/01/2007] [Accepted: 05/03/2007] [Indexed: 11/26/2022]
Abstract
Magnetic resonance imaging provides structural and functional cardiovascular information with excellent soft tissue contrast. Real-time magnetic resonance imaging can guide transcatheter cardiovascular interventions in large animal models and may prove superior to x-ray and adjunct modalities for peripheral vascular, structural heart, and cardiac electrophysiology applications. We describe technical considerations, preclinical work, and early clinical studies in this emerging field.
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Affiliation(s)
- Venkatesh K Raman
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1538, USA
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Raman VK, Lederman RJ. Advances in interventional cardiovascular MRI. CURRENT CARDIOVASCULAR RISK REPORTS 2007. [DOI: 10.1007/s12170-007-0050-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Saborowski O, Saeed M. An overview on the advances in cardiovascular interventional MR imaging. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2007; 20:117-27. [PMID: 17487451 DOI: 10.1007/s10334-007-0074-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2006] [Revised: 03/19/2007] [Accepted: 03/20/2007] [Indexed: 10/23/2022]
Abstract
Interventional cardiovascular magnetic resonance imaging (iCMR) represents a new discipline whose systematic development will foster minimally invasive interventional procedures without radiation exposure. New generations of open, wide and short bore MR scanners and real time sequences made cardiovascular intervention possible. MR compatible endovascular catheters and guide-wires are needed for delivery of devices such as stents or atrial septal defect (ASD) closures. Catheter tracking is based on active and passive approaches. Currently performed MR-guided procedures are used to monitor, navigate and track endovascular catheters and to deliver local therapeutic agents to targets, such as infarcted myocardium and vascular walls. Heating of endovascular MR catheters, guide-wires and devices during imaging still presents high safety risks. MR contrast media improve the capabilities of MR imaging by enhancing blood signal, pathologic targets (such as myocardial infarctions and atherosclerotic plaques), endovascular catheters and by tracking injected therapeutic agents. Labeling injected soluble therapeutic agents, genes or cells with MR contrast media enables interventionalists to ensure the administration of the drugs in the target and to trace their distribution in the targets. The future clinical use of this iCMR technique requires (1) high spatial and temporal resolution imaging, (2) special catheters and devices and (3) effective therapeutic agents, genes or cells. These conditions are available at a low scale at the present time and need to be developed in the near future. Such progress will lead to improved patient care and minimize invasiveness.
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Affiliation(s)
- Olaf Saborowski
- Department of Radiology, University of California San Francisco, 513 Parnassus Avenue, HSW 207B, San Francisco, CA 94143-0628, USA
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Abstract
Because of its superior soft tissue imaging, MRI has become a valuable diagnostic tool in cardiovascular disease. These strengths make MRI attractive to guide therapeutic catheter-based procedures, both conventional and novel. We review how to configure an interventional MRI suite, how MRI catheter devices differ from conventional radiographic catheters, and finally developments in preclinical and investigational clinical applications.
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Affiliation(s)
- Venkatesh K Raman
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1538, USA
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Busch MHJ, Vollmann W, Grönemeyer DHW. Finite volume analysis of temperature effects induced by active MRI implants: 2. Defects on active MRI implants causing hot spots. Biomed Eng Online 2006; 5:35. [PMID: 16729878 PMCID: PMC1513583 DOI: 10.1186/1475-925x-5-35] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Accepted: 05/26/2006] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Active magnetic resonance imaging implants, for example stents, stent grafts or vena cava filters, are constructed as wireless inductively coupled transmit and receive coils. They are built as a resonator tuned to the Larmor frequency of a magnetic resonance system. The resonator can be added to or incorporated within the implant. This technology can counteract the shielding caused by eddy currents inside the metallic implant structure. This may allow getting diagnostic information of the implant lumen (in stent stenosis or thrombosis for example). The electro magnetic rf-pulses during magnetic resonance imaging induce a current in the circuit path of the resonator. A by material fatigue provoked partial rupture of the circuit path or a broken wire with touching surfaces can set up a relatively high resistance on a very short distance, which may behave as a point-like power source, a hot spot, inside the body part the resonator is implanted to. This local power loss inside a small volume can reach (1/4) of the total power loss of the intact resonating circuit, which itself is proportional to the product of the resonator volume and the quality factor and depends as well from the orientation of the resonator with respect to the main magnetic field and the imaging sequence the resonator is exposed to. METHODS First an analytical solution of a hot spot for thermal equilibrium is described. This analytical solution with a definite hot spot power loss represents the worst case scenario for thermal equilibrium inside a homogeneous medium without cooling effects. Starting with this worst case assumptions additional conditions are considered in a numerical simulation, which are more realistic and may make the results less critical. The analytical solution as well as the numerical simulations use the experimental experience of the maximum hot spot power loss of implanted resonators with a definite volume during magnetic resonance imaging investigations. The finite volume analysis calculates the time developing temperature maps for the model of a broken linear metallic wire embedded in tissue. Half of the total hot spot power loss is assumed to diffuse into both wire parts at the location of a defect. The energy is distributed from there by heat conduction. Additionally the effect of blood perfusion and blood flow is respected in some simulations because the simultaneous appearance of all worst case conditions, especially the absence of blood perfusion and blood flow near the hot spot, is very unlikely for vessel implants. RESULTS The analytical solution as worst case scenario as well as the finite volume analysis for near worst case situations show not negligible volumes with critical temperature increases for part of the modeled hot spot situations. MR investigations with a high rf-pulse density lasting below a minute can establish volumes of several cubic millimeters with temperature increases high enough to start cell destruction. Longer exposure times can involve volumes larger than 100 mm3. Even temperature increases in the range of thermal ablation are reached for substantial volumes. MR sequence exposure time and hot spot power loss are the primary factors influencing the volume with critical temperature increases. Wire radius, wire material as well as the physiological parameters blood perfusion and blood flow inside larger vessels reduce the volume with critical temperature increases, but do not exclude a volume with critical tissue heating for resonators with a large product of resonator volume and quality factor. CONCLUSION The worst case scenario assumes thermal equilibrium for a hot spot embedded in homogeneous tissue without any cooling due to blood perfusion or flow. The finite volume analysis can calculate the results for near and not close to worst case conditions. For both cases a substantial volume can reach a critical temperature increase in a short time. The analytical solution, as absolute worst case, points out that resonators with a small product of inductance volume and quality factor (Q V(ind) < 2 cm3) are definitely save. Stents for coronary vessels or resonators used as tracking devices for interventional procedures therefore have no risk of high temperature increases. The finite volume analysis shows for sure that also conditions not close to the worst case reach physiologically critical temperature increases for implants with a large product of inductance volume and quality factor (Q V(ind) > 10 cm3). Such resonators exclude patients from exactly the MRI investigation these devices are made for.
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Affiliation(s)
- Martin HJ Busch
- Grönemeyer Institute for Microtherapy, University of Witten/Herdecke, Universitätsstr. 142, D-44799 Bochum, Germany
| | - Wolfgang Vollmann
- Department of mathematics, physics and chemistry, TFH University of Applied Sciences, Luxemburger Straße 10, D-13353 Berlin, Germany
| | - Dietrich HW Grönemeyer
- Grönemeyer Institute for Microtherapy, University of Witten/Herdecke, Universitätsstr. 142, D-44799 Bochum, Germany
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Mekle R, Hofmann E, Scheffler K, Bilecen D. A polymer-based MR-compatible guidewire: a study to explore new prospects for interventional peripheral magnetic resonance angiography (ipMRA). J Magn Reson Imaging 2006; 23:145-55. [PMID: 16374877 DOI: 10.1002/jmri.20486] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To introduce a newly developed polymer-based and magnetic resonance (MR)-compatible guidewire and to explore its capabilities with respect to interventional peripheral magnetic resonance angiography (ipMRA) in a flow phantom. MATERIALS AND METHODS The guidewire is based on a polyetheretherketone (PEEK) polymer core, and small iron particles are embedded in its coating. A passive device tracking technique was designed utilizing a susceptibility artifact induced by the wire in images acquired with a balanced steady-state free precession (b-SSFP) sequence using small flip angles. The position of the guidewire tip was determined from image intensity maxima and overlayed onto a roadmap in near real-time. Guidewire tracking and balloon angioplasty of an artificial stenosis were attempted in two configurations of a flow phantom. RESULTS Successful passive guidewire tracking was performed for all phantom configurations. Robustness and accuracy of the tracking technique were sufficient for phantom studies. A balloon catheter was placed into the stenosis using the guidewire under complete MR guidance, and subsequent balloon angioplasty yielded improved flow conditions. CONCLUSION The new guidewire is well-suited for clinical application due to an absence of the risk of core fracture and its atraumatic flexible tip. It opens novel prospects for the realization of ipMRA in humans that need to be explored in further studies.
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Affiliation(s)
- Ralf Mekle
- MR-Physics, University of Basel/University Hospital, Basel, Switzerland.
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Affiliation(s)
- Robert J Lederman
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892-1538, USA.
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Venook RD, Hargreaves BA, Gold GE, Conolly SM, Scott GC. Automatic tuning of flexible interventional RF receiver coils. Magn Reson Med 2006; 54:983-93. [PMID: 16155871 DOI: 10.1002/mrm.20616] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Microcontroller-based circuitry was built and tested for automatically tuning flexible RF receiver coils at the touch of a button. This circuitry is robust to 10% changes in probe center frequency, is in line with the scanner, and requires less than 1 s to tune a simple probe. Images were acquired using this circuitry with a varactor-tunable 1-inch flexible probe in a phantom and in an in vitro porcine knee model. The phantom experiments support the use of automatic tuning by demonstrating 30% signal-to-noise ratio (SNR) losses for 5% changes in coil center frequency, in agreement with theoretical calculations. Comparisons between patellofemoral cartilage images obtained using a 3-inch surface coil and the surgically-implanted 1-inch flexible coil reveal a worst-case local SNR advantage of a factor of 4 for the smaller coil. This work confirms that surgically implanted coils can greatly improve resolution in small-field-of-view (FOV) applications, and demonstrates the importance and feasibility of automatically tuning such probes.
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Affiliation(s)
- Ross D Venook
- Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, CA 94305, USA.
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Bilgen M. Inductively-overcoupled coil design for high resolution magnetic resonance imaging. Biomed Eng Online 2006; 5:3. [PMID: 16401343 PMCID: PMC1363722 DOI: 10.1186/1475-925x-5-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2005] [Accepted: 01/09/2006] [Indexed: 11/10/2022] Open
Abstract
Background Maintaining the quality of magnetic resonance images acquired with the current implantable coil technology is challenging in longitudinal studies. To overcome this challenge, the principle of 'inductive overcoupling' is introduced as a method to tune and match a dual coil system. This system consists of an imaging coil built with fixed electrical elements and a matching coil equipped with tuning and matching capabilities. Overcoupling here refers to the condition beyond which the peak of the current in the imaging coil splits. Methods The combined coils are coupled inductively to operate like a transformer. Each coil circuit is electrically represented by equivalent lumped-elements. A theoretical analysis is given to identify the frequency response characteristics of the currents in each coil. The predictions from this analysis are translated into experiments and applied to locally image rat spinal cord at 9.4 T using an implantable coil as the imaging coil and an external volume coil as the matching coil. Results The theoretical analysis indicated that strong coupling between the coils divides the resonance peaks on the response curves of the currents. Once these newly generated peaks were tuned and matched to the desired frequency and impedance of operation, in vivo images were acquired from the rat spinal cord at high quality and high resolution. Conclusion After proper implementation, inductive overcoupling provides a unique opportunity for tuning and matching the coil system, and allows reliable and repeatable acquisitions of magnetic resonance data. This feature is likely to be useful in experimental studies, such as those aimed at longitudinally imaging the rat following spinal cord injury.
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Affiliation(s)
- Mehmet Bilgen
- Hoglund Brain Imaging Center, The University of Kansas Medical School, Kansas City, KS 66160, USA.
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Abstract
Magnetic resonance imaging (MRI), which provides superior soft-tissue imaging and no known harmful effects, has the potential as an alternative modality to guide various medical interventions. This review will focus on MR-guided endovascular interventions and present its current state and future outlook. In the first technical part, enabling technologies such as developments in fast imaging, catheter devices, and visualization techniques are examined. This is followed by a clinical survey that includes proof-of-concept procedures in animals and initial experience in human subjects. In preclinical experiments, MRI has already proven to be valuable. For example, MRI has been used to guide and track targeted cell delivery into or around myocardial infarctions, to guide atrial septal puncture, and to guide the connection of portal and systemic venous circulations. Several investigational MR-guided procedures have already been reported in patients, such as MR-guided cardiac catheterization, invasive imaging of peripheral artery atheromata, selective intraarterial MR angiography, and preliminary angioplasty and stent placement. In addition, MR-assisted transjugular intrahepatic portosystemic shunt procedures in patients have been shown in a novel hybrid double-doughnut x-ray/MRI system. Numerous additional investigational human MR-guided endovascular procedures are now underway in several medical centers around the world. There are also significant hurdles: availability of clinical-grade devices, device-related safety issues, challenges to patient monitoring, and acoustic noise during imaging. The potential of endovascular interventional MRI is great because as a single modality, it combines 3-dimensional anatomic imaging, device localization, hemodynamics, tissue composition, and function.
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Affiliation(s)
- Cengizhan Ozturk
- Cardiovascular Branch, Division of Intramural Research, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
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McVeigh ER, Guttman MA, Kellman P, Raval AN, Lederman RJ. Real-time, Interactive MRI for cardiovascular interventions. Acad Radiol 2005; 12:1121-7. [PMID: 16112512 PMCID: PMC2169205 DOI: 10.1016/j.acra.2005.05.024] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2005] [Revised: 05/29/2005] [Accepted: 02/15/2005] [Indexed: 11/25/2022]
Affiliation(s)
- Elliot R McVeigh
- Laboratory of Cardiac Energetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Building 10, Room B1D416, Bethesda, MD 20892-106, USA.
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Quick HH, Zenge MO, Kuehl H, Kaiser G, Aker S, Massing S, Bosk S, Ladd ME. Interventional magnetic resonance angiography with no strings attached: wireless active catheter visualization. Magn Reson Med 2005; 53:446-55. [PMID: 15678524 DOI: 10.1002/mrm.20347] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Active instrument visualization strategies for interventional MR angiography (MRA) require vascular instruments to be equipped with some type of radiofrequency (RF) coil or dipole RF antenna for MR signal detection. Such visualization strategies traditionally necessitate a connection to the scanner with either coaxial cable or laser fibers. In order to eliminate any wire connection, RF resonators that inductively couple their signal to MR surface coils were implemented into catheters to enable wireless active instrument visualization. Instrument background to contrast-to-noise ratio was systematically investigated as a function of the excitation flip angle. Signal coupling between the catheter RF coil and surface RF coils was evaluated qualitatively and quantitatively as a function of the catheter position and orientation with regard to the static magnetic field B0 and to the surface coils. In vivo evaluation of the instruments was performed in interventional MRA procedures on five pigs under MR guidance. Cartesian and projection reconstruction TrueFISP imaging enabled simultaneous visualization of the instruments and vascular morphology in real time. The implementation of RF resonators enabled robust visualization of the catheter curvature to the very tip. Additionally, the active visualization strategy does not require any wire connection to the scanner and thus does not hamper the interventionalist during the course of an intervention.
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Affiliation(s)
- Harald H Quick
- Department of Diagnostic and Interventional Radiology, University Hospital Essen, MR-Center, Essen, Germany.
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Abstract
Although x-ray fluoroscopy (XRF) has guided diagnostic and therapeutic transcatheter procedures for decades, certain limitations still exist. XRF still visualizes tissue poorly and relies on projection of shadows that do not convey depth information. Adjunctive echocardiography overcomes some of these limitations but still suffers suboptimal or unreliable imaging windows. Furthermore, ionizing radiation exposure in children imparts a cancer risk. An interventional platform using real-time magnetic resonance imaging (MRI) may offer superior image guidance without radiation. Although there are many remaining challenges, but real-time MRI has the potential to revolutionize transcatheter therapeutics.
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Affiliation(s)
- A N Raval
- Cardiovascular Branch, Division of Intramural Research, National Heart Lung and Blood Institute, National Institutes of Health, Building 10, Room 2c713, MSC 1538, Bethesda, MD 20892-1538, USA
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Busch MHJ, Vollmann W, Schnorr J, Grönemeyer DHW. Finite volume analysis of temperature effects induced by active MRI implants with cylindrical symmetry: 1. Properly working devices. Biomed Eng Online 2005; 4:25. [PMID: 15819973 PMCID: PMC1087857 DOI: 10.1186/1475-925x-4-25] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Accepted: 04/08/2005] [Indexed: 11/10/2022] Open
Abstract
Background Active Magnetic Resonance Imaging implants are constructed as resonators tuned to the Larmor frequency of a magnetic resonance system with a specific field strength. The resonating circuit may be embedded into or added to the normal metallic implant structure. The resonators build inductively coupled wireless transmit and receive coils and can amplify the signal, normally decreased by eddy currents, inside metallic structures without affecting the rest of the spin ensemble. During magnetic resonance imaging the resonators generate heat, which is additional to the usual one described by the specific absorption rate. This induces temperature increases of the tissue around the circuit paths and inside the lumen of an active implant and may negatively influence patient safety. Methods This investigation provides an overview of the supplementary power absorbed by active implants with a cylindrical geometry, corresponding to vessel implants such as stents, stent grafts or vena cava filters. The knowledge of the overall absorbed power is used in a finite volume analysis to estimate temperature maps around different implant structures inside homogeneous tissue under worst-case assumptions. The "worst-case scenario" assumes thermal heat conduction without blood perfusion inside the tissue around the implant and mostly without any cooling due to blood flow inside vessels. Results The additional power loss of a resonator is proportional to the volume and the quality factor, as well as the field strength of the MRI system and the specific absorption rate of the applied sequence. For properly working devices the finite volume analysis showed only tolerable heating during MRI investigations in most cases. Only resonators transforming a few hundred mW into heat may reach temperature increases over 5 K. This requires resonators with volumes of several ten cubic centimeters, short inductor circuit paths with only a few 10 cm and a quality factor above ten. Using MR sequences, for which the MRI system manufacturer declares the highest specific absorption rate of 4 W/kg, vascular implants with a realistic construction, size and quality factor do not show temperature increases over a critical value of 5 K. Conclusion The results show dangerous heating for the assumed "worst-case scenario" only for constructions not acceptable for vascular implants. Realistic devices are safe with respect to temperature increases. However, this investigation discusses only properly working devices. Ruptures or partial ruptures of the wires carrying the electric current of the resonance circuits or other defects can set up a power source inside an extremely small volume. The temperature maps around such possible "hot spots" should be analyzed in an additional investigation.
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Affiliation(s)
- Martin HJ Busch
- Research and Development Center for Microtherapy (EFMT), D-44799 Bochum, Germany
- Grönemeyer Institute for Microtherapy, University of Witten/Herdecke, D-44799 Bochum, Germany
| | | | - Jörg Schnorr
- Institut für Radiologie, Charité, Medizinische Fakultät, Humboldt-Universität zu Berlin, D-10117 Berlin, Germany
| | - Dietrich HW Grönemeyer
- Grönemeyer Institute for Microtherapy, University of Witten/Herdecke, D-44799 Bochum, Germany
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Busch M, Vollmann W, Bertsch T, Wetzler R, Bornstedt A, Schnackenburg B, Schnorr J, Kivelitz D, Taupitz M, Grönemeyer D. On the heating of inductively coupled resonators (stents) during MRI examinations. Magn Reson Med 2005; 54:775-82. [PMID: 16149073 DOI: 10.1002/mrm.20618] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Stents that have been implanted to preserve the results of vascular dilatation are frequently affected by in-stent restenosis, which ideally should be followed up by a noninvasive diagnostic modality. Active MRI stents can enable this kind of follow-up, while normal metallic stents can not. The prototype stents investigated in this study were designed as electric resonating circuits without a direct connection to the MR imager, and function as inductively coupled transmit coils. The model of a long solenoid coil is used to describe the additional power loss caused by such resonators. The theoretically estimated temperature increase is verified by measurements for different resonators and discussed for worst-case conditions. The RF power absorption of an active resonator is negligible compared to the total power absorbed during MRI. The local temperature increase observed for prototypes embedded in phantoms is in a range that excludes direct tissue damage. However, ruptures in the conducting structure of a resonator can cause hot spots, which may establish a high local temperature. This hazard can be reduced by designing resonators with a low quality (Q) factor or by setting the circuit slightly off resonance; however, this would lower the nominal amplification for which the resonator was designed.
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Affiliation(s)
- Martin Busch
- Grönemeyer Institut für Mikrotherapie, Universität Witten/Herdecke, Bochum, Germany.
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Feng L, Dumoulin CL, Dashnaw S, Darrow RD, Guhde R, Delapaz RL, Bishop PL, Pile-Spellman J. Transfemoral catheterization of carotid arteries with real-time MR imaging guidance in pigs. Radiology 2004; 234:551-7. [PMID: 15591433 DOI: 10.1148/radiol.2341031951] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
All procedures and protocols were approved by the institutional animal care and use committee of Columbia University. To determine whether transfemoral catheterization of the carotid arteries can be performed entirely with real-time magnetic resonance (MR) imaging guidance, the authors catheterized the carotid arteries in six domestic pigs by using active-tracking catheters and guidewires and MR tracking software created for neurovascular procedures. The carotid arteries were successfully catheterized 24 times, on average within 5 minutes after insertion of the catheter into the femoral artery. Results demonstrated the feasibility of performing transfemoral catheterization of the carotid arteries with active MR tracking devices in a conventional MR imaging unit.
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Affiliation(s)
- Lei Feng
- Department of Radiology, Columbia University, 177 Fort Washington Ave, MHB 8SK, New York, NY 10032, USA
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Walsh EG, Holton AD, Brott BC, Venugopalan R, Anayiotos AS. Magnetic resonance phase velocity mapping through NiTi stents in a flow phantom model. J Magn Reson Imaging 2004; 21:59-65. [PMID: 15611949 DOI: 10.1002/jmri.20238] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
PURPOSE To assess constant and pulsatile flow velocity within the lumen of a peripheral NiTi stent using phase velocity mapping for comparison with independent assessments of flow velocity in a phantom model. MATERIALS AND METHODS A 9 x 20-mm stent installed in flexible tubing was placed in a phantom filled with stationary fluid. Constant and pulsatile flow (produced by a pump programmed to produce a simulation of the carotid artery flow) was assessed using phase velocity mapping at 4.1 T (for constant flow) and at 1.5 T (for pulsatile flow). In all cases 256 x 256 gradient echo phase velocity maps were acquired. For the pulsatile flow condition, cine images with acquisition gated to the pump cycle were acquired with 40 msec temporal resolution across the simulated cardiac cycle. Computed flow volume rates were compared with fluid volume collection for the constant flow model, and with ultrasonic Doppler flow meter measurements for the pulsatile model. RESULTS The data showed that volume flow rate assessments by phase velocity mapping agreed with independent measurements within 10% to 15%. CONCLUSION Phase velocity mapping of the lumen of peripheral size NiTi stents is possible in an in vitro model.
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Affiliation(s)
- Edward G Walsh
- Department of Biomedical Engineering, University of Alabama at Birmingham, Birmingham, Alabama, USA
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Trost DW, Zhang HL, Prince MR, Winchester PA, Wang Y, Watts R, Sos TA. Three-dimensional MR angiography in imaging platinum alloy stents. J Magn Reson Imaging 2004; 20:975-80. [PMID: 15558574 DOI: 10.1002/jmri.20209] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To evaluate visualization inside platinum stents with three-dimensional contrast-enhanced magnetic resonance angiography (CE-MRA). MATERIALS AND METHODS Breath-hold three-dimensional gadolinium (Gd) MRA was performed on 18 patients with 22 platinum stents in the renal (n = 18), celiac (n = 1), superior mesenteric (n = 1), and iliac (n = 2) arteries. Electronic calibers were used to measure the lumen diameter within the stent and just distal to the stent to calculate percent stenosis. MRA accuracy was determined from the difference between percent stenosis measured on MRA and digital subtracted angiography (DSA). The patients were imaged at flip angles of 45 degrees , 60 degrees , 75 degrees , 90 degrees , and 150 degrees . RESULTS MRA demonstrated the stent lumen in all of the patients, with a mean difference between MRA and DSA of 21%. For stents oriented parallel to B0 (iliac arteries) the difference was only 10%, as compared to 22% for stents perpendicular to B0. The flip angle with the best agreement between MRA and DSA was 75 degrees (16%). CONCLUSION The lumen of a platinum stent can be imaged with three-dimensional CE-MRA, although grading of restenosis has limited accuracy. The best results were obtained with a flip angle of 75 degrees and for stents in the iliac arteries parallel to B0.
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Affiliation(s)
- David W Trost
- Department of Radiology, Weill Cornell Medical College, New York, New York 10022, USA
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Abstract
Minimally invasive interventional radiological procedures, such as balloon angioplasty, stent placement or coiling of aneurysms, play an increasingly important role in the treatment of patients suffering from vascular disease. The non-destructive nature of magnetic resonance imaging (MRI), its ability to combine the acquisition of high quality anatomical images and functional information, such as blood flow velocities, perfusion and diffusion, together with its inherent three dimensionality and tomographic imaging capacities, have been advocated as advantages of using the MRI technique for guidance of endovascular radiological interventions. Within this light, endovascular interventional MRI has emerged as an interesting and promising new branch of interventional radiology. In this review article, the authors will give an overview of the most important issues related to this field. In this context, we will focus on the prerequisites for endovascular interventional MRI to come to maturity. In particular, the various approaches for device tracking that were proposed will be discussed and categorized. Furthermore, dedicated MRI systems, safety and compatibility issues and promising applications that could become clinical practice in the future will be discussed.
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Affiliation(s)
- L W Bartels
- Department of Radiology, Image Sciences Institute, University Medical Center Utrecht, Heidelberglaan 100, Room E.01.335, 3584 CX Utrecht, The Netherlands.
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