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Dudysheva N, Mauconduit F, Abdeddaim R, Gapais PF, Hosseinnezhadian S, Dubois M, Amadon A, Boulant N, Hertz-Pannier L, Vignaud A. The restricted SAR protocol: A method to assess MRI coil prototypes in an unconditionally safe manner. Magn Reson Med 2024; 91:1723-1734. [PMID: 38084471 DOI: 10.1002/mrm.29962] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 10/24/2023] [Accepted: 11/17/2023] [Indexed: 02/03/2024]
Abstract
PURPOSE Testing an RF coil prototype on subjects involves laborious verifications to ensure its safety. In particular, it requires preliminary electromagnetic simulations and their validations on phantoms to accurately predict the specific absorption rate (SAR). For coil design validation with a simpler safety procedure, the restricted SAR (rS) mode is proposed, enabling representative first experiments in vivo. The goal of the developed approach is to accelerate the transition of a custom coil system from prototype to clinical use. METHODS The restricted specific absorption rate (SAR) (rS) mode imposes a radical limitation on the transmitted RF power based on a worst-case scenario of local RF power absorption. The limitations used are independent of the SAR spatial distribution, making this approach unconditionally safe. The developed rS protocol contains the sequences required for coil evaluation and satisfies the imposed rS conditions. It provides a quantitative characterization of the coil transmission and reception profiles and a qualitative evaluation of the anatomical images. Protocol validation was performed on commercial and pre-industrial prototype coils on a small cohort of healthy volunteers. RESULTS The proposed rS protocol enables coil evaluation within an acquisition time compatible with common clinical protocol duration. The total time of all evaluation steps does not exceed 17 min. At the same time, the global SAR remains 100 times less than the International Electrotechnical Commission safety limit for played sequences. CONCLUSION The rS protocol allows characterizing and comparing coil prototypes on volunteers without extensive electromagnetic calculations and phantom validations in an unconditionally safe way.
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Affiliation(s)
- Natalia Dudysheva
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
- Multiwave Imaging, Marseille, France
| | - Franck Mauconduit
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Redha Abdeddaim
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, Institut Marseille Imaging, Marseille, France
| | | | | | | | - Alexis Amadon
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Nicolas Boulant
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Lucie Hertz-Pannier
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
| | - Alexandre Vignaud
- Paris-Saclay University, CEA, CNRS, BAOBAB, NeuroSpin, Gif-sur-Yvette, France
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Nohava L, Czerny R, Tik M, Wurzer D, Laistler E, Frass-Kriegl R. Citizen science approach to assessing patient perception of MRI with flexible radiofrequency coils. Sci Rep 2024; 14:2811. [PMID: 38307928 PMCID: PMC10837436 DOI: 10.1038/s41598-024-53364-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 01/30/2024] [Indexed: 02/04/2024] Open
Abstract
Magnetic Resonance Imaging (MRI) is a major medical imaging modality, which is non-invasive and provides unique soft tissue contrast without ionizing radiation. The successful completion of MRI exams critically depends on patient compliance, and, thus patient comfort. The design, appearance and usability of local MRI radiofrequency (RF) coils potentially influences the patients' perception of the exam. However, systematic investigations and empirical evidence for these aspects are missing. A questionnaire specifically evaluating the impact of RF coils on patient comfort in MRI would be a valuable addition to clinical studies comparing the performance of novel flexible RF coils with standard rigid coils. This paper describes the development of such a questionnaire in the scope of a citizen science (CS) initiative conducted with a group of students at the upper secondary school level. In this work, the CS initiative is presented in the format of a case report and its impact on scientific projects and the students' education is outlined. The resulting questionnaire is made available in German and English so as to be directly applicable by researchers working on the clinical evaluation of novel RF coils or the comfort evaluation of specific hardware setups in general.
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Affiliation(s)
- Lena Nohava
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Raphaela Czerny
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Martin Tik
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Dagmar Wurzer
- Bundes(real)gymnasium BG/BRG Keimgasse, Mödling, Austria
| | - Elmar Laistler
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria
| | - Roberta Frass-Kriegl
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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Overson DK, Darnell D, Robb F, Song AW, Truong TK. Flexible multi-purpose integrated RF/shim coil array for MRI and localized B 0 shimming. Magn Reson Med 2024; 91:842-849. [PMID: 37849021 PMCID: PMC10842526 DOI: 10.1002/mrm.29891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 09/22/2023] [Accepted: 09/27/2023] [Indexed: 10/19/2023]
Abstract
PURPOSE To develop a flexible, lightweight, and multi-purpose integrated parallel reception, excitation, and shimming (iPRES) coil array that can conform to the subject's anatomy and perform MR imaging and localized B0 shimming in different anatomical regions with a high SNR, shimming performance, ease of positioning, and subject comfort. METHODS A four-channel flexible iPRES coil array was constructed by enabling RF and direct currents to flow on the same flexible coil elements for imaging and shimming, respectively. Shimming experiments were performed with the coil array wrapped around the knee or neck of healthy subjects to demonstrate its high shimming performance and versatility. Additionally, its SNR and shimming performance in the knee were compared to those obtained with the coil array wrapped around a larger rigid tube designed to fit most knee sizes. RESULTS Shimming with the coil array wrapped around the knee or neck resulted in an average reduction in B0 RMSE of 50.1% and 40.5% relative to first-order and second-order spherical harmonic shimming, respectively, and substantially reduced distortions in DWI images. In contrast, shimming the knee with the coil array wrapped around the rigid tube only provided a 29.6% reduction in B0 RMSE, whereas the SNR was reduced by 58.7%. CONCLUSION The flexible iPRES coil array can conform to different anatomical regions and perform imaging and localized B0 shimming with a higher SNR, shimming performance, ease of positioning, and comfort compared to a rigid iPRES coil array, which should be valuable for many applications throughout the human body.
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Affiliation(s)
- Devon Karl Overson
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, USA
- Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA
| | - Dean Darnell
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, USA
- Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA
| | | | - Allen W Song
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, USA
- Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA
| | - Trong-Kha Truong
- Brain Imaging and Analysis Center, Duke University, Durham, North Carolina, USA
- Medical Physics Graduate Program, Duke University, Durham, North Carolina, USA
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Obermann M, Nohava L, Frass-Kriegl R, Soanca O, Ginefri JC, Felblinger J, Clauser P, Baltzer PA, Laistler E. Panoramic Magnetic Resonance Imaging of the Breast With a Wearable Coil Vest. Invest Radiol 2023; 58:799-810. [PMID: 37227137 PMCID: PMC10581436 DOI: 10.1097/rli.0000000000000991] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2023] [Accepted: 04/21/2023] [Indexed: 05/26/2023]
Abstract
BACKGROUND Breast cancer, the most common malignant cancer in women worldwide, is typically diagnosed by x-ray mammography, which is an unpleasant procedure, has low sensitivity in women with dense breasts, and involves ionizing radiation. Breast magnetic resonance imaging (MRI) is the most sensitive imaging modality and works without ionizing radiation, but is currently constrained to the prone imaging position due to suboptimal hardware, therefore hampering the clinical workflow. OBJECTIVES The aim of this work is to improve image quality in breast MRI, to simplify the clinical workflow, shorten measurement time, and achieve consistency in breast shape with other procedures such as ultrasound, surgery, and radiation therapy. MATERIALS AND METHODS To this end, we propose "panoramic breast MRI"-an approach combining a wearable radiofrequency coil for 3 T breast MRI (the "BraCoil"), acquisition in the supine position, and a panoramic visualization of the images. We demonstrate the potential of panoramic breast MRI in a pilot study on 12 healthy volunteers and 1 patient, and compare it to the state of the art. RESULTS With the BraCoil, we demonstrate up to 3-fold signal-to-noise ratio compared with clinical standard coils and acceleration factors up to 6 × 4. Panoramic visualization of supine breast images reduces the number of slices to be viewed by a factor of 2-4. CONCLUSIONS Panoramic breast MRI allows for high-quality diagnostic imaging and facilitated correlation to other diagnostic and interventional procedures. The developed wearable radiofrequency coil in combination with dedicated image processing has the potential to improve patient comfort while enabling more time-efficient breast MRI compared with clinical coils.
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Chai S, Yan X. Miniature and flexible Bazooka balun for high-field MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 356:107577. [PMID: 37897924 PMCID: PMC10842505 DOI: 10.1016/j.jmr.2023.107577] [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: 05/18/2023] [Revised: 10/10/2023] [Accepted: 10/23/2023] [Indexed: 10/30/2023]
Abstract
Flexible coils offer improved patient comfort and better imaging quality. However, rigid and bulky baluns in RF coils limit flexibility and manufacturing. A miniaturized and flexible balun design was proposed to address this issue. It replaced rigid components with an ultra-flexible rubber tube and a flexible coaxial capacitor. Simulations validated the concept, and bench tests confirmed its performance, including a measured common-mode rejection ratio of -15.8 dB. The flexible balun was integrated into a 4-channel coil array, evaluating impedance changes caused by the "hand effect." Compared to coils without the balun, the flexible coil with the proposed balun showed improved robustness in impedance matching and inter-element couplings. Transmit efficiency of the flexible coil with the balun was compared to coils without a balun and with a rigid, shielded cable trap. Results demonstrated that the proposed balun circuit maintained high transmit efficiency. Overall, the flexible balun design offers a promising solution for improving the flexibility and performance of RF coil arrays in MRI applications.
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Affiliation(s)
- Shuyang Chai
- Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN 37232, USA; Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Xinqiang Yan
- Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN 37232, USA; 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.
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Nohava L, Obermann M, Frass-Kriegl R, Soanca O, Laistler E. A modular system of flexible receive-only coil arrays for 3 T Magnetic Resonance Imaging. Z Med Phys 2023:S0939-3889(23)00070-3. [PMID: 37258388 DOI: 10.1016/j.zemedi.2023.05.002] [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: 02/15/2023] [Revised: 04/18/2023] [Accepted: 05/08/2023] [Indexed: 06/02/2023]
Abstract
Flexible form-fitting radiofrequency coils provide high signal-to-noise ratio (SNR) for magnetic resonance imaging (MRI), and in array configuration large anatomical areas of interest can be covered. We propose a modular system - "ModFlex"- of flexible lightweight 4-channel coaxial coil arrays for 3 T MRI. We investigated the performance difference between commercial reference coils and 8- and 16-channel ModFlex receive-only array systems. In vivo, six anatomical targets in four regions of interest - the neck, the ankle, the spine and the hip - were imaged with the novel coil array system. The versatility of ModFlex and the robustness of the coil characteristics for different use cases is demonstrated. We measured an SNR gain for 4 out of 6 and similar SNR for 2 out of 6 anatomical target regions as compared to commercial reference coils. Parallel imaging capabilities are comparable to standard coils in hip and neck imaging, but ModFlex outperforms standard coils in ankle and spine imaging. High SNR combined with high acceleration possibilities enables faster imaging workflows and/or high-resolution MR acquisitions. The coil's versatility is beneficial for use cases with varying subject sizes and could improve patient comfort.
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Affiliation(s)
- Lena Nohava
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
| | - Michael Obermann
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
| | - Roberta Frass-Kriegl
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
| | - Onisim Soanca
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
| | - Elmar Laistler
- High Field MR Center, Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria.
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Baren JP, Rowbotham E, Robinson P. Acromioclavicular Joint Injury and Repair. Semin Musculoskelet Radiol 2022; 26:597-610. [DOI: 10.1055/s-0042-1750726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
AbstractThe acromioclavicular (AC) joint is commonly injured in athletes participating in contact and overhead throwing sports. Injuries range from simple sprains to complete ligamentous disruption, and they are classified by the established Rockwood grading system. High-grade injuries are associated with fractures around the AC joint and disruption of the superior shoulder suspensory complex, a ring of osseous and ligamentous structures at the superior aspect of the shoulder. Radiographs are the mainstay of imaging of the AC joint, with magnetic resonance imaging reserved for high-grade injuries to aid classification and plan surgical management. Low-grade AC joint injuries tend to be managed conservatively, but a wide range of surgical procedures have been described for higher grade injuries and fractures around the AC joint. This review illustrates the anatomy of the AC joint and surrounding structures, the imaging features of AC joint injury, and the most commonly performed methods of reconstruction and their complications.
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Affiliation(s)
- James P. Baren
- Department of Musculoskeletal Radiology, Leeds Teaching Hospitals, Leeds, United Kingdom
| | - Emma Rowbotham
- Department of Musculoskeletal Radiology, Leeds Teaching Hospitals, Leeds, United Kingdom
- NIHR Leeds Biomedical Research Centre, Leeds Teaching Hospitals Trust, University of Leeds, Leeds, United Kingdom
| | - Philip Robinson
- Department of Musculoskeletal Radiology, Leeds Teaching Hospitals, Leeds, United Kingdom
- NIHR Leeds Biomedical Research Centre, Leeds Teaching Hospitals Trust, University of Leeds, Leeds, United Kingdom
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Priovoulos N, Roos T, Ipek Ö, Meliado EF, Nkrumah RO, Klomp DWJ, van der Zwaag W. A local multi-transmit coil combined with a high-density receive array for cerebellar fMRI at 7 T. NMR IN BIOMEDICINE 2021; 34:e4586. [PMID: 34231292 PMCID: PMC8519055 DOI: 10.1002/nbm.4586] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 06/09/2021] [Accepted: 06/22/2021] [Indexed: 06/13/2023]
Abstract
The human cerebellum is involved in a wide array of functions, ranging from motor control to cognitive control, and as such is of great neuroscientific interest. However, its function is underexplored in vivo, due to its small size, its dense structure and its placement at the bottom of the brain, where transmit and receive fields are suboptimal. In this study, we combined two dense coil arrays of 16 small surface receive elements each with a transmit array of three antenna elements to improve BOLD sensitivity in the human cerebellum at 7 T. Our results showed improved B1+ and SNR close to the surface as well as g-factor gains compared with a commercial coil designed for whole-head imaging. This resulted in improved signal stability and large gains in the spatial extent of the activation close to the surface (<3.5 cm), while good performance was retained deeper in the cerebellum. Modulating the phase of the transmit elements of the head coil to constructively interfere in the cerebellum improved the B1+ , resulting in a temporal SNR gain. Overall, our results show that a dedicated transmit array along with the SNR gains of surface coil arrays can improve cerebellar imaging, at the cost of a decreased field of view and increased signal inhomogeneity.
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Affiliation(s)
- Nikos Priovoulos
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
| | - Thomas Roos
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
| | - Özlem Ipek
- Department of Biomedical Engineering, School of Biomedical Engineering & Imaging SciencesKing's College LondonLondonUK
| | - Ettore F. Meliado
- Image Sciences InstituteUniversity Medical Center UtrechtUtrechtNetherlands
| | - Richard O. Nkrumah
- Department of Biomedical Engineering, School of Biomedical Engineering & Imaging SciencesKing's College LondonLondonUK
| | - Dennis W. J. Klomp
- Image Sciences InstituteUniversity Medical Center UtrechtUtrechtNetherlands
| | - Wietske van der Zwaag
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
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Vazquez F, Marrufo O, Solis-Najera SE, Martin R, Rodriguez AO. External Waveguide Magnetic Resonance Imaging for lower limbs at 3 T. Med Phys 2021; 49:158-168. [PMID: 34633673 DOI: 10.1002/mp.15281] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 09/01/2021] [Accepted: 09/21/2021] [Indexed: 11/09/2022] Open
Abstract
INTRODUCTION We report a method based on the travelling-wave MRI approach, in order to acquire images of human lower limbs with an external waveguide at 3 T. METHOD We use a parallel-plate waveguide and an RF surface coil for reception, while a whole-body birdcage is used for transmission. The waveguide and the surface coil are located right outside the magnet, in the MR conditional devices zone. We ran numerical simulations to investigate the B1 field generated by the surface coil located at one of the waveguides, as well as a saline-solution phantom positioned on the opposite side (150 cm away) inside the magnet. RESULTS We obtained phantom images by varying the distance between the coil and the phantom, in order to investigate the signal-to-noise ratio and to validate our numerical simulations. Lower limb images of a healthy volunteer were also acquired, demonstrating the viability of this approach. Standard pulse sequences were used and no physical modifications were made to the MR imager. CONCLUSIONS These numerical and experimental results show that travelling-wave MRI can produce high-quality images with only a simple waveguide and an RF coil located outside the magnet. This can be particularly favorable when acquiring images of lower limbs requiring a larger field of view.
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Affiliation(s)
- F Vazquez
- Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Mexico City, 04510, Mexico
| | - O Marrufo
- Department of Neuroimage, Instituto Nacional de Neurologia y Neurocirugia MVS, Mexico City, 14269, Mexico
| | - S E Solis-Najera
- Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Mexico City, 04510, Mexico
| | - R Martin
- Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Mexico City, 04510, Mexico
| | - A O Rodriguez
- Department of Electrical Engineering, Universidad Autonoma Metropolitama Iztapalapa, Mexico City, 09340, Mexico
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Motovilova E, Tan ET, Taracila V, Vincent JM, Grafendorfer T, Shin J, Potter HG, Robb FJL, Sneag DB, Winkler SA. Stretchable self-tuning MRI receive coils based on liquid metal technology (LiquiTune). Sci Rep 2021; 11:16228. [PMID: 34376703 PMCID: PMC8355233 DOI: 10.1038/s41598-021-95335-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2021] [Accepted: 07/23/2021] [Indexed: 01/14/2023] Open
Abstract
Magnetic resonance imaging systems rely on signal detection via radiofrequency coil arrays which, ideally, need to provide both bendability and form-fitting stretchability to conform to the imaging volume. However, most commercial coils are rigid and of fixed size with a substantial mean offset distance of the coil from the anatomy, which compromises the spatial resolution and diagnostic image quality as well as patient comfort. Here, we propose a soft and stretchable receive coil concept based on liquid metal and ultra-stretchable polymer that conforms closely to a desired anatomy. Moreover, its smart geometry provides a self-tuning mechanism to maintain a stable resonance frequency over a wide range of elongation levels. Theoretical analysis and numerical simulations were experimentally confirmed and demonstrated that the proposed coil withstood the unwanted frequency detuning typically observed with other stretchable coils (0.4% for the proposed coil as compared to 4% for a comparable control coil). Moreover, the signal-to-noise ratio of the proposed coil increased by more than 60% as compared to a typical, rigid, commercial coil.
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Affiliation(s)
- Elizaveta Motovilova
- grid.5386.8000000041936877XDepartment of Radiology, Weill Cornell Medicine, New York, NY 10065 USA ,grid.239915.50000 0001 2285 8823Department of Radiology, Hospital for Special Surgery, New York, NY 10021 USA
| | - Ek Tsoon Tan
- grid.239915.50000 0001 2285 8823Department of Radiology, Hospital for Special Surgery, New York, NY 10021 USA
| | - Victor Taracila
- grid.418143.b0000 0001 0943 0267GE Healthcare, Aurora, OH USA
| | - Jana M. Vincent
- grid.418143.b0000 0001 0943 0267GE Healthcare, Aurora, OH USA
| | | | - James Shin
- grid.5386.8000000041936877XDepartment of Radiology, Weill Cornell Medicine, New York, NY 10065 USA
| | - Hollis G. Potter
- grid.239915.50000 0001 2285 8823Department of Radiology, Hospital for Special Surgery, New York, NY 10021 USA
| | | | - Darryl B. Sneag
- grid.239915.50000 0001 2285 8823Department of Radiology, Hospital for Special Surgery, New York, NY 10021 USA
| | - Simone A. Winkler
- grid.5386.8000000041936877XDepartment of Radiology, Weill Cornell Medicine, New York, NY 10065 USA
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11
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Nohava L, Czerny R, Roat S, Obermann M, Kuehne A, Frass-Kriegl R, Felblinger J, Ginefri JC, Laistler E. Flexible Multi-Turn Multi-Gap Coaxial RF Coils: Design Concept and Implementation for Magnetic Resonance Imaging at 3 and 7 Tesla. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:1267-1278. [PMID: 33439836 DOI: 10.1109/tmi.2021.3051390] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Magnetic resonance has become a backbone of medical imaging but suffers from inherently low sensitivity. This can be alleviated by improved radio frequency (RF) coils. Multi-turn multi-gap coaxial coils (MTMG-CCs) introduced in this work are flexible, form-fitting RF coils extending the concept of the single-turn single-gap CC by introducing multiple cable turns and/or gaps. It is demonstrated that this enables free choice of the coil diameter, and thus, optimizing it for the application to a certain anatomical site, while operating at the self-resonance frequency. An equivalent circuit for MTMG-CCs is modeled to predict their resonance frequency. Possible configurations regarding size, number of turns and gaps, and cable types for different B 0 field strengths are calculated. Standard copper wire loop coils (SCs) and flexible CCs made from commercial coaxial cable were fabricated as receive-only coils for 3 T and transmit/receive coils at 7 T with diameters between 4 and 15 cm. Electromagnetic simulations are used to investigate the currents on MTMG-CCs, and demonstrate comparable specific absorption rate of 7 T CCs and SCs. Signal-to-noise ratio (SNR), transmit efficiency, and active detuning performance of CCs were compared in bench tests and MR experiments. For the form-fitted receive-only CCs at 3 T no significant SNR degradation was found as compared to flat SCs on a balloon phantom. Form-fitted transmit/receive CCs at 7 T showed higher transmit efficiency and SNR. MTMG-CCs can be sized to optimize sensitivity, are flexible and lightweight, and could therefore enable the fabrication of wearable coils with improved patient comfort.
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12
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Port A, Luechinger R, Brunner DO, Pruessmann KP. Elastomer coils for wearable MR detection. Magn Reson Med 2021; 85:2882-2891. [PMID: 33433044 DOI: 10.1002/mrm.28662] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 11/20/2020] [Accepted: 12/07/2020] [Indexed: 01/06/2023]
Abstract
PURPOSE To explore the use of conductive elastomer for MR signal detection and the utility of this approach for wearable detector arrays. METHODS An elastomer filled with silver microparticles was used to form stretchable radiofrequency coils for MR detection. Their electrical performance in terms of the Qunloaded and Q ratio was assessed in the relaxed state and under repeated strain up to 40%. In a phantom imaging study, the signal-to-noise ratio yield of conductive elastomer coils was compared with that of a reference copper coil. Four elastomer coils were integrated with a stretchable textile substrate to form a wearable array for knee imaging. The array was employed for multiple-angle and kinematic knee imaging in vivo. RESULTS The elastomer coils proved highly stretchable and mechanically robust. Upon repeated stretching by 20%, a medium-sized coil element settled at Qunloaded of 42 in the relaxed state and 32 at full strain, reflecting sample-noise dominance. The signal-to-noise ratio of elastomer coils was found to be 8% to 16% lower than that achieved with a conventional copper coil. Multiple-angle and kinematic knee imaging with the wearable array yielded high-quality results indicating robustness of detection performance against stretching and warping of the array. CONCLUSION Conductive elastomer is a viable material for MR detection. Coils made from this material reconcile high stretchability and adequate electrical performance with ease of manufacturing. Conductive elastomer also offers inherent restoring forces and is readily washable and sanitizable, making it an excellent basis of wearable detector front ends.
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Affiliation(s)
- Andreas Port
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Roger Luechinger
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - David O Brunner
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
| | - Klaas P Pruessmann
- Institute for Biomedical Engineering, ETH Zurich and University of Zurich, Zurich, Switzerland
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Ahmad SF, Kim YC, Choi IC, Kim HD. Recent Progress in Birdcage RF Coil Technology for MRI System. Diagnostics (Basel) 2020; 10:diagnostics10121017. [PMID: 33261167 PMCID: PMC7759766 DOI: 10.3390/diagnostics10121017] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 11/23/2020] [Accepted: 11/26/2020] [Indexed: 11/16/2022] Open
Abstract
The radio frequency (RF) coil is one of the key components of the magnetic resonance imaging (MRI) system. It has a significant impact on the performance of the nuclear magnetic resonance (NMR) detection. Among numerous practical designs of RF coils for NMR imaging, the birdcage RF coil is the most popular choice from low field to ultra-high field MRI systems. In the transmission mode, it can establish a strong and homogeneous transverse magnetic field B1 for any element at its Larmor frequency. Similarly, in the reception mode, it exhibits extremely high sensitivity for the detection of even faint NMR signals from the volume of interest. Despite the sophisticated 3D structure of the birdcage coil, the developments in the design, analysis, and implementation technologies during the past decade have rendered the development of the birdcage coils quite reasonable. This article provides a detailed review of the recent progress in the birdcage RF coil technology for the MRI system.
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Affiliation(s)
- Sheikh Faisal Ahmad
- Institute of Advanced Convergence Technology, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea; (S.F.A.); (Y.C.K.); (I.C.C.)
| | - Young Cheol Kim
- Institute of Advanced Convergence Technology, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea; (S.F.A.); (Y.C.K.); (I.C.C.)
| | - Ick Chang Choi
- Institute of Advanced Convergence Technology, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea; (S.F.A.); (Y.C.K.); (I.C.C.)
| | - Hyun Deok Kim
- School of Electronics Engineering, College of IT Engineering, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Korea
- Correspondence: ; Tel.: +82-53-940-8678
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Abstract
OBJECTIVE. The Adaptive Image Receive (AIR) radiofrequency coil is an emergent technology that is lightweight and flexible and exhibits electrical characteristics that overcome many of the limitations of traditional rigid coil designs. The purpose of this study was to apply the AIR coil for whole-brain imaging and compare the performance of a prototype AIR coil array with the performance of conventional head coils. SUBJECTS AND METHODS. A phantom and 15 healthy adult participants were imaged. A prototype 16-channel head AIR coil was compared with conventional 8-and 32-channel head coils using clinically available MRI sequences. During consensus review, two board-certified neuroradiologists graded the AIR coil compared with an 8-channel coil and a 32-channel coil on a 5-point ordinal scale in multiple categories. One- and two-sided Wilcoxon signed rank tests were performed. Noise covariance matrices and geometry factor (g-factor) maps were calculated. RESULTS. The signal-to-noise ratio, structural sharpness, and overall image quality scores of the prototype 16-channel AIR coil were better than those of the 8-channel coil but were not as good as those of the 32-channel coil. Noise covariance matrices showed stable performance of the AIR coil across participants. The median g-factors for the 16-channel AIR coil were, overall, less than those of the 8-channel coil but were greater than those of the 32-channel coil. CONCLUSION. On average, the prototype 16-channel head AIR coil outperformed a conventional 8-channel head coil but did not perform as well as a conventional 32-channel head coil. This study shows the feasibility of the novel AIR coil technology for imaging the brain and provides insight for future coil design improvements.
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Collick BD, Behzadnezhad B, Hurley SA, Mathew NK, Behdad N, Lindsay SA, Robb F, Stormont RS, McMillan AB. Rapid development of application-specific flexible MRI receive coils. Phys Med Biol 2020; 65:19NT01. [PMID: 32975219 PMCID: PMC8064628 DOI: 10.1088/1361-6560/abaffb] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Over the last 30 years, there have been dramatic changes in phased array coil technology leading to increasing channel density and parallel imaging functionality. Current receiver array coils are rigid and often mismatched to patient's size. Recently there has been a move towards flexible coil technology, which is more conformal to the human anatomy. Despite the advances of so-called flexible surface coil arrays, these coils are still relatively rigid and limited in terms of design conformability, compromising signal-to-noise ratio (SNR) for flexibility, and are not designed for optimum parallel imaging performance. The purpose of this study is to report on the development and characterization of a 15-channel flexible foot and ankle coil, rapidly designed and constructed using highly decoupled radio-frequency (RF) coil elements. Coil performance was evaluated by performing SNR and g-factor measurements. In vivo testing was performed in a healthy volunteer using both the 15-channel coil and a commercially available 8-channel foot coil. The highly decoupled elements used in this design allow for extremely rapid development and prototyping of application-specific coils for different patient sizes (adult vs child) with minimal additional design consideration in terms of coil overlap and geometry. Image quality was comparable to a commercially available RF coil.
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Affiliation(s)
- B D Collick
- Department of Radiology, University of Wisconsin, Madison, WI 53705, United States of America. Author B D Collick and author B Behzadnezhad contributed equally to this work
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Brunnquell CL, Hoff MN, Balu N, Nguyen XV, Oztek MA, Haynor DR. Making Magnets More Attractive: Physics and Engineering Contributions to Patient Comfort in MRI. Top Magn Reson Imaging 2020; 29:167-174. [PMID: 32541257 DOI: 10.1097/rmr.0000000000000246] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Patient comfort is an important factor of a successful magnetic resonance (MR) examination, and improvements in the patient's MR scanning experience can contribute to improved image quality, diagnostic accuracy, and efficiency in the radiology department, and therefore reduced cost. Magnet designs that are more open and accessible, reduced auditory noise of MR examinations, light and flexible radiofrequency (RF) coils, and faster motion-insensitive imaging techniques can all significantly improve the patient experience in MR imaging. In this work, we review the design, development, and implementation of these physics and engineering approaches to improve patient comfort.
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Affiliation(s)
- Christina L Brunnquell
- Department of Radiology, University of Washington, Seattle, WA Department of Radiology, The Ohio State University Wexler Medical Center, Columbus, OH
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Detector clothes for MRI: A wearable array receiver based on liquid metal in elastic tubes. Sci Rep 2020; 10:8844. [PMID: 32483259 PMCID: PMC7264329 DOI: 10.1038/s41598-020-65634-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Accepted: 05/06/2020] [Indexed: 11/08/2022] Open
Abstract
In modern magnetic resonance imaging, signal detection is performed by dense arrays of radiofrequency resonators. Tight-fitting arrays boost the sensitivity and speed of imaging. However, current devices are rigid and cage-like at the expense of patient comfort. They also constrain posture, limiting the examination of joints. For better ergonomics and versatility, detectors should be flexible, adapt to individual anatomy, and follow posture. Towards this goal, the present work proposes a novel design based on resonators formed by liquid metal in polymer tubes. Textile integration creates lightweight, elastic devices that are worn like pieces of clothing. A liquid-metal array tailored to the human knee is shown to deliver competitive image quality while self-adapting to individual anatomy and adding the ability to image flexion of the joint. Relative to other options for stretchable conductors, liquid metal in elastic tubes stands out by reconciling excellent electrical and mechanical properties with ease of manufacturing.
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Movahedian Attar F, Kirilina E, Haenelt D, Pine KJ, Trampel R, Edwards LJ, Weiskopf N. Mapping Short Association Fibers in the Early Cortical Visual Processing Stream Using In Vivo Diffusion Tractography. Cereb Cortex 2020; 30:4496-4514. [PMID: 32297628 PMCID: PMC7325803 DOI: 10.1093/cercor/bhaa049] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Short association fibers (U-fibers) connect proximal cortical areas and constitute the majority of white matter connections in the human brain. U-fibers play an important role in brain development, function, and pathology but are underrepresented in current descriptions of the human brain connectome, primarily due to methodological challenges in diffusion magnetic resonance imaging (dMRI) of these fibers. High spatial resolution and dedicated fiber and tractography models are required to reliably map the U-fibers. Moreover, limited quantitative knowledge of their geometry and distribution makes validation of U-fiber tractography challenging. Submillimeter resolution diffusion MRI—facilitated by a cutting-edge MRI scanner with 300 mT/m maximum gradient amplitude—was used to map U-fiber connectivity between primary and secondary visual cortical areas (V1 and V2, respectively) in vivo. V1 and V2 retinotopic maps were obtained using functional MRI at 7T. The mapped V1–V2 connectivity was retinotopically organized, demonstrating higher connectivity for retinotopically corresponding areas in V1 and V2 as expected. The results were highly reproducible, as demonstrated by repeated measurements in the same participants and by an independent replication group study. This study demonstrates a robust U-fiber connectivity mapping in vivo and is an important step toward construction of a more complete human brain connectome.
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Affiliation(s)
- Fakhereh Movahedian Attar
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany
| | - Evgeniya Kirilina
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany.,Department of Education and Psychology, Center for Cognitive Neuroscience Berlin, Free University Berlin, 14195 Berlin, Germany
| | - Daniel Haenelt
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany
| | - Kerrin J Pine
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany
| | - Robert Trampel
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany
| | - Luke J Edwards
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany
| | - Nikolaus Weiskopf
- Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany.,Felix Bloch Institute for Solid State Physics, Faculty of Physics and Earth Sciences, Leipzig University, 04109 Leipzig, Germany
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