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Rahimi F, Nurzed B, Eigentler TW, Berangi M, Oberacker E, Kuehne A, Ghadjar P, Millward JM, Schuhmann R, Niendorf T. Helmet Radio Frequency Phased Array Applicators Enhance Thermal Magnetic Resonance of Brain Tumors. Bioengineering (Basel) 2024; 11:733. [PMID: 39061815 PMCID: PMC11273942 DOI: 10.3390/bioengineering11070733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2024] [Revised: 06/29/2024] [Accepted: 07/05/2024] [Indexed: 07/28/2024] Open
Abstract
Thermal Magnetic Resonance (ThermalMR) integrates Magnetic Resonance Imaging (MRI) diagnostics and targeted radio-frequency (RF) heating in a single theranostic device. The requirements for MRI (magnetic field) and targeted RF heating (electric field) govern the design of ThermalMR applicators. We hypothesize that helmet RF applicators (HPA) improve the efficacy of ThermalMR of brain tumors versus an annular phased RF array (APA). An HPA was designed using eight broadband self-grounded bow-tie (SGBT) antennae plus two SGBTs placed on top of the head. An APA of 10 equally spaced SGBTs was used as a reference. Electromagnetic field (EMF) simulations were performed for a test object (phantom) and a human head model. For a clinical scenario, the head model was modified with a tumor volume obtained from a patient with glioblastoma multiforme. To assess performance, we introduced multi-target evaluation (MTE) to ensure whole-brain slice accessibility. We implemented time multiplexed vector field shaping to optimize RF excitation. Our EMF and temperature simulations demonstrate that the HPA improves performance criteria critical to MRI and enhances targeted RF and temperature focusing versus the APA. Our findings are a foundation for the experimental implementation and application of a HPA en route to ThermalMR of brain tumors.
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Affiliation(s)
- Faezeh Rahimi
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
- FG Theoretische Elektrotechnik, Technical University of Berlin, 10587 Berlin, Germany;
| | - Bilguun Nurzed
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
- Technische Universität Berlin, Chair of Medical Engineering, 10587 Berlin, Germany;
- Berliner Hochschule für Technik, 13353 Berlin, Germany
| | - Thomas W. Eigentler
- Technische Universität Berlin, Chair of Medical Engineering, 10587 Berlin, Germany;
| | - Mostafa Berangi
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
- MRI.TOOLS GmbH, 13125 Berlin, Germany;
| | - Eva Oberacker
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
| | | | - Pirus Ghadjar
- Department Radiation Oncology, Charité–Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin and Humboldt-Universität zu Berlin, Augustenburger Platz 1, 13353 Berlin, Germany;
| | - Jason M. Millward
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
- Experimental and Clinical Research Center, Joint Cooperation between Charité Unversitätsmedizin and the Max-Delbrück Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
| | - Rolf Schuhmann
- FG Theoretische Elektrotechnik, Technical University of Berlin, 10587 Berlin, Germany;
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility, Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany; (B.N.); (M.B.); (E.O.); (J.M.M.)
- MRI.TOOLS GmbH, 13125 Berlin, Germany;
- Experimental and Clinical Research Center, Joint Cooperation between Charité Unversitätsmedizin and the Max-Delbrück Center for Molecular Medicine in the Helmholtz Association, 13125 Berlin, Germany
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Giannakopoulos II, Georgakis IP, Sodickson DK, Lattanzi R. Computational methods for the estimation of ideal current patterns in realistic human models. Magn Reson Med 2024; 91:760-772. [PMID: 37800398 DOI: 10.1002/mrm.29864] [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: 05/15/2023] [Revised: 08/25/2023] [Accepted: 08/28/2023] [Indexed: 10/07/2023]
Abstract
PURPOSE To introduce a method for the estimation of the ideal current patterns (ICP) that yield optimal signal-to-noise ratio (SNR) for realistic heterogeneous tissue models in MRI. THEORY AND METHODS The ICP were calculated for different surfaces that resembled typical radiofrequency (RF) coil formers. We constructed numerical electromagnetic (EM) bases to accurately represent EM fields generated by RF current sources located on the current-bearing surfaces. Using these fields as excitations, we solved the volume integral equation and computed the EM fields in the sample. The fields were appropriately weighted to calculate the optimal SNR and the corresponding ICP. We demonstrated how to qualitatively use ICP to guide the design of a coil array to maximize SNR inside a head model. RESULTS In agreement with previous analytic work, ICP formed large distributed loops for voxels in the middle of the sample and alternated between a single loop and a figure-eight shape for a voxel 3-cm deep in the sample's cortex. For the latter voxel, a surface quadrature loop array inspired by the shape of the ICP reached87 . 5 % $$ 87.5\% $$ of the optimal SNR at 3T, whereas a single loop placed above the voxel reached only55 . 7 % $$ 55.7\% $$ of the optimal SNR. At 7T, the performance of the two designs decreased to79 . 7 % $$ 79.7\% $$ and49 . 8 % $$ 49.8\% $$ , respectively, suggesting that loops could be suboptimal at ultra-high field MRI. CONCLUSION ICP can be calculated for human tissue models, potentially guiding the design of application-specific RF coil arrays.
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Affiliation(s)
- Ilias I Giannakopoulos
- The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
| | | | - Daniel K Sodickson
- The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
| | - Riccardo Lattanzi
- The Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
- Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University Grossman School of Medicine, New York, New York, USA
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Nurzed B, Kuehne A, Aigner CS, Schmitter S, Niendorf T, Eigentler TW. Radiofrequency antenna concepts for human cardiac MR at 14.0 T. MAGMA (NEW YORK, N.Y.) 2023; 36:257-277. [PMID: 36920549 PMCID: PMC10140016 DOI: 10.1007/s10334-023-01075-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 02/23/2023] [Accepted: 02/27/2023] [Indexed: 04/28/2023]
Abstract
OBJECTIVE To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx). MATERIALS AND METHODS RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B1+) uniformity and efficiency in the heart of the human voxel model. B1+ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR10g) were examined at 7.0 T and 14.0 T. RESULTS At 14.0 T static pTx revealed a minimum B1+ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B1+ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B1+ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR10g < 5.25 W/kg. DISCUSSION MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.
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Affiliation(s)
- Bilguun Nurzed
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
| | | | | | | | - Thoralf Niendorf
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany.
- MRI.TOOLS GmbH, Berlin, Germany.
- Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
| | - Thomas Wilhelm Eigentler
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
- Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
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Sappo CR, Gallego GL, Grissom WA, Yan X. On the design and manufacturing of miniaturized microstripline power splitters for driving multicoil transmit arrays with arbitrary ratios at 7 T. NMR IN BIOMEDICINE 2022; 35:e4793. [PMID: 35772938 PMCID: PMC11193150 DOI: 10.1002/nbm.4793] [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: 12/11/2021] [Revised: 06/02/2022] [Accepted: 06/26/2022] [Indexed: 06/15/2023]
Abstract
The purpose of the current study was to implement unequal microstrip power splitters for parallel transmission at 7 T that are optimized for size and loss and that can be configured for a wide range of power ratios. The splitters will enable the use of more transmit coils without a corresponding increase in the number of transmit channels or amplifiers to control specific absorption rate, shorten RF pulses, and shim inhomogeneous RF fields. Wilkinson unequal power splitters based on a novel microstrip network design were optimized to minimize their size under 8 cm in length and 9 cm in width, enabling them to be included in coil housing or cascaded in multiple stages. Splitters were designed and constructed for a wide range of output power ratios at 298 MHz. Simulations and bench tests were performed for each ratio, and a methodology was established to adapt the designs to other ratios and frequencies. The designs and code are open source and can be reproduced as is or reconfigured. The single-stage designs achieved good matches and isolations between output ports (worst isolation -15.9 dB, worst match -15.1 dB). A two-stage cascaded (one input to four outputs) power splitter with 1:2.5, 1:10, 1:3, and 1:6 ratio outputs was constructed. The worst isolation between output ports was -19.7 dB in simulation and the worst match of the three ports was -17.8 dB. The measured ratios for one- and two-stage boards were within 10% of the theoretical ratios. The power-handling capability of the smallest trace was approximately 70 W. Power loss for the one- and two-stage boards ranged from 1% to 3% in simulation compared with 5.1% to 7.2% on the bench. It was concluded that Wilkinson unequal microstrip power splitters can be implemented with a small board size (low height) and low loss, and across a wide range of output power ratios. The splitters can be cascaded in multiple stages while maintaining the expected ratios and low loss. This will enable the construction of large fixed transmit array-compression matrices with low loss.
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Affiliation(s)
- Charlotte R Sappo
- Vanderbilt University Institute of Imaging Science, Nashville, TN, United States
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
| | - Gabriela L Gallego
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
| | - William A Grissom
- Vanderbilt University Institute of Imaging Science, Nashville, TN, United States
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
- Department of Radiology, Vanderbilt University, Nashville, TN, United States
- Department of Electrical and Computer Engineering, Vanderbilt University, Nashville, TN, United States
| | - Xinqiang Yan
- Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, United States
- Department of Radiology, Vanderbilt University, Nashville, TN, United States
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Georgakis IP, Villena JF, Polimeridis AG, Lattanzi R. Novel Numerical Basis Sets for Electromagnetic Field Expansion in Arbitrary Inhomogeneous Objects. IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION 2022; 70:8227-8241. [PMID: 37124164 PMCID: PMC10147338 DOI: 10.1109/tap.2022.3177566] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
We investigated how to construct low-order subspace basis sets to accurately represent electromagnetic fields generated within inhomogeneous arbitrary objects by radio-frequency sources external to a Huygen's surface. The basis generation relies on the singular value decomposition of Green's functions integro-differential operators which makes it feasible to derive a reduced-order yet stable model. We present a detailed study of the theoretical and numerical requisites for generating such basis, and show how it can be used to calculate performance limits in magnetic resonance imaging applications. Finally, we propose a novel numerical framework for the computation of characteristic modes of arbitrary inhomogeneous objects. We validated accuracy and convergence properties of the numerical basis against a complete analytical basis in the case of a uniform spherical object. We showed that the discretization of the Huygens's surface has a minimal effect on the accuracy of the calculations, which mainly depended on the electromagnetic solver resolution and order of approximation.
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Affiliation(s)
- Ioannis P Georgakis
- Center for Advanced Imaging Innovation and Research (CAIR), Department of Radiology, New York University Grossman School of Medicine, NY, USA
| | | | | | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAIR), Department of Radiology, New York University Grossman School of Medicine, NY, USA
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Eigentler TW, Kuehne A, Boehmert L, Dietrich S, Els A, Waiczies H, Niendorf T. 32-Channel self-grounded bow-tie transceiver array for cardiac MR at 7.0T. Magn Reson Med 2021; 86:2862-2879. [PMID: 34169546 DOI: 10.1002/mrm.28885] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2021] [Revised: 04/20/2021] [Accepted: 05/18/2021] [Indexed: 12/17/2022]
Abstract
PURPOSE Design, implementation, evaluation, and application of a 32-channel Self-Grounded Bow-Tie (SGBT) transceiver array for cardiac MR (CMR) at 7.0T. METHODS The array consists of 32 compact SGBT building blocks. Transmission field ( B 1 + ) shimming and radiofrequency safety assessment were performed with numerical simulations and benchmarked against phantom experiments. In vivo B 1 + efficiency mapping was conducted with actual flip angle imaging. The array's applicability for accelerated high spatial resolution 2D FLASH CINE imaging of the heart was examined in a volunteer study (n = 7). RESULTS B 1 + shimming provided a uniform field distribution suitable for female and male subjects. Phantom studies demonstrated an excellent agreement between simulated and measured B 1 + efficiency maps (7% mean difference). The SGBT array afforded a spatial resolution of (0.8 × 0.8 × 2.5) mm3 for 2D CINE FLASH which is by a factor of 12 superior to standardized cardiovascular MR (CMR) protocols. The density of the SGBT array supports 1D acceleration of up to R = 4 (mean signal-to-noise ratio (whole heart) ≥ 16.7, mean contrast-to-noise ratio ≥ 13.5) without impairing image quality significantly. CONCLUSION The compact SGBT building block facilitates a modular high-density array that supports accelerated and high spatial resolution CMR at 7.0T. The array provides a technological basis for future clinical assessment of parallel transmission techniques.
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Affiliation(s)
- Thomas Wilhelm Eigentler
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| | | | - Laura Boehmert
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Sebastian Dietrich
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Antje Els
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | | | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (B.U.F.F.), Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.,MRI.TOOLS GmbH, Berlin, Germany.,Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max Delbrück Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany
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Francavilla MA, Lefkimmiatis S, Villena JF, G Polimeridis A. Maxwell parallel imaging. Magn Reson Med 2021; 86:1573-1585. [PMID: 33733495 DOI: 10.1002/mrm.28718] [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: 08/20/2020] [Revised: 01/15/2021] [Accepted: 01/15/2021] [Indexed: 11/09/2022]
Abstract
PURPOSE To develop a general framework for parallel imaging (PI) with the use of Maxwell regularization for the estimation of the sensitivity maps (SMs) and constrained optimization for the parameter-free image reconstruction. THEORY AND METHODS Certain characteristics of both the SMs and the images are routinely used to regularize the otherwise ill-posed optimization-based joint reconstruction from highly accelerated PI data. In this paper, we rely on a fundamental property of SMs-they are solutions of Maxwell equations-we construct the subspace of all possible SM distributions supported in a given field-of-view, and we promote solutions of SMs that belong in this subspace. In addition, we propose a constrained optimization scheme for the image reconstruction, as a second step, once an accurate estimation of the SMs is available. The resulting method, dubbed Maxwell parallel imaging (MPI), works for both 2D and 3D, with Cartesian and radial trajectories, and minimal calibration signals. RESULTS The effectiveness of MPI is illustrated for various undersampling schemes, including radial, variable-density Poisson-disc, and Cartesian, and is compared against the state-of-the-art PI methods. Finally, we include some numerical experiments that demonstrate the memory footprint reduction of the constructed Maxwell basis with the help of tensor decomposition, thus allowing the use of MPI for full 3D image reconstructions. CONCLUSION The MPI framework provides a physics-inspired optimization method for the accurate and efficient image reconstruction from arbitrary accelerated scans.
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