51
|
Zivkovic I, de Castro CA, Webb A. Design and characterization of an eight-element passively fed meander-dipole array with improved specific absorption rate efficiency for 7 T body imaging. NMR IN BIOMEDICINE 2019; 32:e4106. [PMID: 31131944 PMCID: PMC6771742 DOI: 10.1002/nbm.4106] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 03/14/2019] [Accepted: 04/02/2019] [Indexed: 06/09/2023]
Abstract
OBJECTIVE To evaluate the transmit efficiency and specific absorption rate (SAR) efficiency of a new eight-element passively fed meander-dipole antenna array designed for body MRI at 7 T, and to compare these values with a conventional directly fed meander-dipole array. METHODS The main radiating element of the passively fed dipole is printed on one side of a dielectric substrate and is capacitively coupled to a shorter feeding element (connected to the coaxial cable) printed on the opposite side of the substrate. The transmit (B1+ ) field and SAR were simulated on a phantom and on a human voxel model for both a passively fed and a directly fed single element. Two eight-channel arrays containing, respectively, directly and passively fed meander dipoles were then simulated, and experimental B1+ maps and T2 -weighted spin echo images of the prostate were obtained in vivo for four healthy volunteers. RESULTS In simulations, the mean transmit efficiency (B1+ per square root input power) value in the prostate was ~ 12.5% lower, and the maximum 10 g average SAR was 44% lower for the array containing passively fed dipoles, resulting in ~ 15% higher SAR efficiency for the passively fed array. In vivo RF-shimmed turbo spin echo images were acquired from both arrays, and showed image SNRs within 5% of one another. CONCLUSION A passive-feeding network for meander-dipole antennas has been shown to be a simple method to increase the SAR efficiency of a multi-element array used for body imaging at high fields. We hypothesize that the main reason for the increase in SAR efficiency is the storage of the strong conservative electric field in the dielectric between the feeding element and the radiating element of the dipole. The passive-feeding approach can be generalized to other dipole geometries and configurations.
Collapse
Affiliation(s)
- Irena Zivkovic
- C.J. Gorter Center for High Field MRI, Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| | | | - Andrew Webb
- C.J. Gorter Center for High Field MRI, Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| |
Collapse
|
52
|
A Platform for 4-Channel Parallel Transmission MRI at 3 T: Demonstration of Reduced Radiofrequency Heating in a Test Object Containing an Implanted Wire. J Med Biol Eng 2019. [DOI: 10.1007/s40846-019-00478-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
|
53
|
Erturk MA, Li X, Van de Moortele PF, Ugurbil K, Metzger GJ. Evolution of UHF Body Imaging in the Human Torso at 7T: Technology, Applications, and Future Directions. Top Magn Reson Imaging 2019; 28:101-124. [PMID: 31188271 PMCID: PMC6587233 DOI: 10.1097/rmr.0000000000000202] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/13/2023]
Abstract
The potential value of ultrahigh field (UHF) magnetic resonance imaging (MRI) and spectroscopy to biomedical research and in clinical applications drives the development of technologies to overcome its many challenges. The increased difficulties of imaging the human torso compared with the head include its overall size, the dimensions and location of its anatomic targets, the increased prevalence and magnitude of physiologic effects, the limited availability of tailored RF coils, and the necessary transmit chain hardware. Tackling these issues involves addressing notoriously inhomogeneous transmit B1 (B1) fields, limitations in peak B1, larger spatial variations of the static magnetic field B0, and patient safety issues related to implants and local RF power deposition. However, as research institutions and vendors continue to innovate, the potential gains are beginning to be realized. Solutions overcoming the unique challenges associated with imaging the human torso are reviewed as are current studies capitalizing on the benefits of UHF in several anatomies and applications. As the field progresses, strategies associated with the RF system architecture, calibration methods, RF pulse optimization, and power monitoring need to be further integrated into the MRI systems making what are currently complex processes more streamlined. Meanwhile, the UHF MRI community must seize the opportunity to build upon what have been so far proof of principle and feasibility studies and begin to further explore the true impact in both research and the clinic.
Collapse
Affiliation(s)
- M Arcan Erturk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN
| | | | | | | | | |
Collapse
|
54
|
Abstract
Radiofrequency (RF) coils are an essential part of the magnetic resonance (MR) system. To exploit the inherently higher signal-to-noise ratio at ultrahigh magnetic fields (UHF), research sites were forced to build up expertise in RF coil development, as the number of commercially available RF coils were limited. In addition, an integrated transmit body RF coil, which is well-established at MR systems of lower field strength, is still missing at UHF due to technical and physical constraints. This review article provides a brief recapitulation of RF characteristics and RF coils in general to introduce terminology and RF-related parameters, and will then provide an extensive overview of current state-of-the-art RF coils used for MRI from head to toe at 7 Tesla. Finally, a section on RF safety will briefly discuss challenges in performing a safety assessment for custom-designed RF coils, and issues arising from the interaction of the RF field and potentially implanted medical devices.
Collapse
Affiliation(s)
- Oliver Kraff
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
- High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| |
Collapse
|
55
|
Rietsch SHG, Brunheim S, Orzada S, Voelker MN, Maderwald S, Bitz AK, Gratz M, Ladd ME, Quick HH. Development and evaluation of a 16-channel receive-only RF coil to improve 7T ultra-high field body MRI with focus on the spine. Magn Reson Med 2019; 82:796-810. [PMID: 30924181 DOI: 10.1002/mrm.27731] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2018] [Revised: 01/02/2019] [Accepted: 01/27/2019] [Indexed: 12/21/2022]
Abstract
PURPOSE A 16-channel receive (16Rx) radiofrequency (RF) array for 7T ultra-high field body MR imaging is presented. The coil is evaluated in conjunction with a 16-channel transmit/receive (16TxRx) coil and additionally with a 32-channel transmit/receive (32TxRx) remote body coil for RF transmit and serving as receive references. METHODS The 16Rx array consists of 16 octagonal overlapping loops connected to custom-built detuning boards with preamplifiers. Performance metrics like noise correlation, g-factors, and signal-to-noise ratio gain were compared between 4 different RF coil configurations. In vivo body imaging was performed in volunteers using radiofrequency shimming, time interleaved acquisition of modes (TIAMO), and 2D spatially selective excitation using parallel transmit (pTx) in the spine. RESULTS Lower g-factors were obtained when using the 16Rx coil in addition to the 16TxRx array coil configuration versus the 16TxRx array alone. Distinct signal-to-noise ratio gain using the 16Rx coil could be demonstrated in the spine region both for a comparison with the 16TxRx coil (>50% gain) in vivo and the 32TxRx coil (>240% gain) in a phantom. The 16Rx coil was successfully applied to improve anatomical imaging in the abdomen and 2D spatially selective excitation in the spine of volunteers. CONCLUSION The novel 16-channel Rx-array as an add-on to multichannel TxRx RF coil configurations provides increased signal-to-noise ratio, lower g-factors, and thus improves 7T ultra-high field body MR imaging.
Collapse
Affiliation(s)
- Stefan H G Rietsch
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Sascha Brunheim
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Maximilian N Voelker
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Andreas K Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, University of Applied Sciences Aachen, Aachen, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Faculty of Physics and Astronomy and Faculty of Medicine, University of Heidelberg, Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High-Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| |
Collapse
|
56
|
Krikken E, Steensma BR, Voogt IJ, Luijten PR, Klomp DW, Raaijmakers AJ, Wijnen JP. Homogeneous B 1+ for bilateral breast imaging at 7 T using a five dipole transmit array merged with a high density receive loop array. NMR IN BIOMEDICINE 2019; 32:e4039. [PMID: 30489661 PMCID: PMC6587506 DOI: 10.1002/nbm.4039] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 09/24/2018] [Accepted: 10/12/2018] [Indexed: 06/09/2023]
Abstract
To explore the use of five meandering dipole antennas in a multi-transmit setup, combined with a high density receive array for breast imaging at 7 T for improved penetration depth and more homogeneous B1 field. Five meandering dipole antennas and 30 receiver loops were positioned on two cups around the breasts. Finite difference time domain simulations were performed to evaluate RF safety limits of the transmit setup. Scattering parameters of the transmit setup and coupling between the antennas and the detuned loops were measured. In vivo parallel imaging performance was investigated for various acceleration factors. After RF shimming, a B1 map, a T1 -weighted image, and a T2 -weighted image were acquired to assess B1 efficiency, uniformity in contrast weighting, and imaging performance in clinical applications. The maximum achievable local SAR10g value was 7.0 W/kg for 5 × 1 W accepted power. The dipoles were tuned and matched to a maximum reflection of -11.8 dB, and a maximum inter-element coupling of -14.2 dB. The maximum coupling between the antennas and the receive loops was -18.2 dB and the mean noise correlation for the 30 receive loops 7.83 ± 8.69%. In vivo measurements showed an increased field of view, which reached to the axilla, and a high transmit efficiency. This coil enabled the acquisition of T1 -weighted images with a high spatial resolution of 0.7 mm3 isotropic and T2 -weighted spin echo images with uniformly weighted contrast.
Collapse
Affiliation(s)
- Erwin Krikken
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Bart R. Steensma
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Ingmar J. Voogt
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Peter R. Luijten
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Dennis W.J. Klomp
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| | - Alexander J.E. Raaijmakers
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
- Department of Biomedical EngineeringEindhoven University of TechnologyEindhovenThe Netherlands
| | - Jannie P. Wijnen
- Department of RadiologyUniversity Medical Center UtrechtUtrechtThe Netherlands
| |
Collapse
|
57
|
Santini T, Zhao Y, Wood S, Krishnamurthy N, Kim J, Farhat N, Alkhateeb S, Martins T, Koo M, Zhao T, Aizenstein HJ, Ibrahim TS. In-vivo and numerical analysis of the eigenmodes produced by a multi-level Tic-Tac-Toe head transmit array for 7 Tesla MRI. PLoS One 2018; 13:e0206127. [PMID: 30481187 PMCID: PMC6258503 DOI: 10.1371/journal.pone.0206127] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Accepted: 10/08/2018] [Indexed: 11/18/2022] Open
Abstract
Radio-frequency (RF) field inhomogeneities and higher levels of specific absorption rate (SAR) still present great challenges in ultrahigh-field (UHF) MRI. In this study, an in-depth analysis of the eigenmodes of a 20-channel transmit Tic-Tac-Toe (TTT) RF array for 7T neuro MRI is presented. The eigenmodes were calculated for five different Z levels (along the static magnetic field direction) of the coil. Four eigenmodes were obtained for each Z level (composed of 4 excitation ports), and they were named based on the characteristics of their field distributions: quadrature, opposite-phase, anti-quadrature, and zero-phase. Corresponding finite-difference time-domain (FDTD) simulations were performed and experimental B1+ field maps were acquired using a homogeneous spherical phantom and human head (in-vivo). The quadrature mode is the most efficient and it excites the central brain regions; the opposite-phase mode excites the brain peripheral regions; anti-quadrature mode excites the head periphery; and the zero-phase mode excites cerebellum and temporal lobes. Using this RF array, up to five eigenmodes (from five different Z levels) can be simultaneously excited. The superposition of these modes has the potential to produce homogeneous excitation with full brain coverage and low levels of SAR at 7T MRI.
Collapse
Affiliation(s)
- Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Yujuan Zhao
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Sossena Wood
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Narayanan Krishnamurthy
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Junghwan Kim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Nadim Farhat
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Salem Alkhateeb
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Tiago Martins
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Minseok Koo
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
| | - Tiejun Zhao
- Siemens Medical Solutions, Pittsburgh, PA, United States of America
| | - Howard J. Aizenstein
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
- Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh, PA, United States of America
| | - Tamer S. Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA, United States of America
- Department of Psychiatry, University of Pittsburgh Medical Center, Pittsburgh, PA, United States of America
- * E-mail:
| |
Collapse
|
58
|
Solomakha G, Leeuwen CV, Raaijmakers A, Simovski C, Popugaev A, Abdeddaim R, Melchakova I, Glybovski S. The dual‐mode dipole: A new array element for 7T body imaging with reduced SAR. Magn Reson Med 2018; 81:1459-1469. [PMID: 30226636 DOI: 10.1002/mrm.27485] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 07/05/2018] [Accepted: 07/14/2018] [Indexed: 01/13/2023]
Abstract
PURPOSE To design and test an RF-coil based on two orthogonal eigenmodes in a pair of coupled dipoles, for 7 Tesla body imaging with improved SAR, called dual-mode dipole. METHODS The proposed coil consists of two dipoles and creates two orthogonal field distributions in a sample (the even and odd modes). A coupler used to excite the modes was miniaturized with the conductor track routing technique. Numerical simulations of the dual-mode dipole in the presence of a homogeneous phantom were performed. Moreover, an array of such coils was simulated with a voxel body model. For comparison, a fractionated dipole combined with a surface loop coil was also simulated. Both coils were tested in a 7 Tesla MRI system on a phantom. Subsequently four dual-mode dipoles or dipole/loop combinations were used for a comparison of imaging performance in a human volunteer. RESULTS Using the even mode of the dual-mode dipole showed 70% SAR reduction in comparison to the fractionated dipole while having the same B 1 + in the prostate region. The odd mode of the dual-mode dipole showed a performance comparable to the surface loop both for SAR and B1 efficiency. The obtained results showed that the proposed coil while creating lower SAR gave images of the same quality as the reference coil. CONCLUSIONS It was demonstrated that the array of dual-mode dipoles provided the same SNR and prostate imaging quality as the reference array, while demonstrating lower SAR. This is due to a smoother current distribution over a sample surface.
Collapse
Affiliation(s)
- Georgiy Solomakha
- Department of Nanophotonics and Metamaterials ITMO University Saint Petersburg Russian Federation
| | - Carel van Leeuwen
- Department of Radiology University Medical Center Utrecht Utrecht The Netherlands
| | - Alexander Raaijmakers
- Department of Radiology University Medical Center Utrecht Utrecht The Netherlands
- Department of Biomedical Engineering Eindhoven University of Technology Eindhoven The Netherlands
| | - Constantin Simovski
- Department of Electronics and Nanoengineering Aalto University, School of Electrical Engineering Espoo Finland
| | - Alexander Popugaev
- RF and SatCom Systems Fraunhofer Institute for Integrated Circuits IIS Erlangen Germany
| | - Redha Abdeddaim
- Aix Marseille University, CNRS, Centrale Marseille, Institut Fresnel Marseille France
| | - Irina Melchakova
- Department of Nanophotonics and Metamaterials ITMO University Saint Petersburg Russian Federation
| | - Stanislav Glybovski
- Department of Nanophotonics and Metamaterials ITMO University Saint Petersburg Russian Federation
| |
Collapse
|
59
|
Steensma BR, Voogt I, van der Werf AJ, van den Berg CA, Luijten PR, Klomp DW, Raaijmakers AJ. Design of a forward view antenna for prostate imaging at 7 T. NMR IN BIOMEDICINE 2018; 31:e3993. [PMID: 30022543 PMCID: PMC6175442 DOI: 10.1002/nbm.3993] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 06/07/2018] [Accepted: 06/08/2018] [Indexed: 05/19/2023]
Abstract
PURPOSE To design a forward view antenna for prostate imaging at 7 T, which is placed between the legs of the subject in addition to a dipole array. MATERIALS AND METHODS The forward view antenna is realized by placing a cross-dipole antenna at the end of a small rectangular waveguide. Quadrature drive of the cross-dipole can excite a circularly polarized wave propagating along the axial direction to and from the prostate region. Functioning of the forward view antenna is validated by comparing measurements and simulations. Antenna performance is evaluated by numerical simulations and measurements at 7 T. RESULTS Simulations of B1+ on a phantom are in good correspondence with measurements. Simulations on a human model indicate that the signal-to-noise ratio (SNR), specific absorption rate (SAR) efficiency and SAR increase when adding the forward view antenna to a previously published dipole array. The SNR increases by up to 18% when adding the forward view antenna as a receive antenna to an eight-channel dipole array in vivo. CONCLUSIONS A design for a forward view antenna is presented and evaluated. SNR improvements up to 18% are demonstrated when adding the forward view antenna to a dipole array.
Collapse
Affiliation(s)
| | - Ingmar Voogt
- University Medical Center UtrechtUtrechtthe Netherlands
| | | | | | | | | | | |
Collapse
|
60
|
Jaeschke SH, Robson MD, Hess AT. Cardiac gating using scattering of an 8-channel parallel transmit coil at 7T. Magn Reson Med 2018; 80:633-640. [PMID: 29230860 PMCID: PMC5947608 DOI: 10.1002/mrm.27038] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 10/27/2017] [Accepted: 11/17/2017] [Indexed: 12/24/2022]
Abstract
PURPOSE To establish a cardiac signal from scattering matrix or scattering coefficient measurements made on a 7T 8-channel parallel transmit (pTx) system, and to evaluate its use for cardiac gating. METHODS Measurements of the scattering matrix and scattering coefficients were acquired using a monitoring pulse sequence and during a standard cine acquisition, respectively. Postprocessing used an independent component analysis and gating feature identification. The effect of the phase of the excitation radiofrequency (RF) field ( B1+ shim) on the cardiac signal was simulated for multiple B1+ shim configurations, and cine images were reconstructed from both the scattering coefficients and electrocardiogram (ECG). RESULTS The cardiac motion signal was successfully identified in all subjects with a mean signal-to-noise ratio of 33.1 and 5.7 using the scattering matrix and scattering coefficient measurements, respectively. The dominant gating feature in the cardiac signal was a peak aligned with end-systole that occurred on average at 311 and 391 ms after the ECG trigger, with a mean standard deviation of 13.4 and 18.1 ms relative to ECG when using the scattering matrix and scattering coefficients measurements, respectively. The scattering coefficients showed a dependence on B1+ shim with some shim configurations not showing any cardiac signal. Cine images were successfully reconstructed using the scattering coefficients with minimal differences compared to those using ECG. CONCLUSION We have shown that the scattering of a pTx RF coil can be used to estimate a cardiac signal, and that scattering matrix and coefficients can be used to cardiac gate MRI acquisitions with the scattering matrix providing a superior cardiac signal. Magn Reson Med 80:633-640, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Collapse
Affiliation(s)
- Sven H.F. Jaeschke
- University of Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe HospitalOxfordUnited Kingdom
| | - Matthew D. Robson
- University of Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe HospitalOxfordUnited Kingdom
| | - Aaron T. Hess
- University of Oxford Centre for Clinical Magnetic Resonance Research, John Radcliffe HospitalOxfordUnited Kingdom
| |
Collapse
|
61
|
Garwood M, Uğurbil K. RF pulse methods for use with surface coils: Frequency-modulated pulses and parallel transmission. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2018; 291:84-93. [PMID: 29705035 PMCID: PMC5943143 DOI: 10.1016/j.jmr.2018.01.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Accepted: 01/24/2018] [Indexed: 06/08/2023]
Abstract
The first use of a surface coil to obtain a 31P NMR spectrum from an intact rat by Ackerman and colleagues initiated a revolution in magnetic resonance imaging (MRI) and spectroscopy (MRS). Today, we take it for granted that one can detect signals in regions external to an RF coil; at the time, however, this concept was most unusual. In the approximately four decade long period since its introduction, this simple idea gave birth to an increasing number of innovations that has led to transformative changes in the way we collect data in an in vivo magnetic resonance experiment, particularly with MRI of humans. These innovations include spatial localization and/or encoding based on the non-uniform B1 field generated by the surface coil, leading to new spectroscopic localization methods, image acceleration, and unique RF pulses that deal with B1 inhomogeneities and even reduce power deposition. Without the surface coil, many of the major technological advances that define the extraordinary success of MRI in clinical diagnosis and in biomedical research, as exemplified by projects like the Human Connectome Project, would not have been possible.
Collapse
Affiliation(s)
- Michael Garwood
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA.
| | - Kamil Uğurbil
- Center for Magnetic Resonance Research and Department of Radiology, University of Minnesota, Minneapolis, MN 55455 USA
| |
Collapse
|
62
|
Rietsch SHG, Orzada S, Maderwald S, Brunheim S, Philips BWJ, Scheenen TWJ, Ladd ME, Quick HH. 7T ultra-high field body MR imaging with an 8-channel transmit/32-channel receive radiofrequency coil array. Med Phys 2018; 45:2978-2990. [PMID: 29679498 DOI: 10.1002/mp.12931] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Revised: 03/20/2018] [Accepted: 03/30/2018] [Indexed: 12/11/2022] Open
Abstract
PURPOSE In this work, a combined body coil array with eight transmit/receive (Tx/Rx) meander elements and with 24 receive-only (Rx) loops (8Tx/32Rx) was developed and evaluated in comparison with an 8-channel transmit/receive body array (8Tx/Rx) based on meander elements serving as the reference standard. METHODS Systematic evaluation of the RF array was performed on a body-sized phantom. Body imaging at 7T was performed in six volunteers in the body regions pelvis, abdomen, and heart. Coil characteristics such as signal-to-noise ratio, acceleration capability, g-factors, S-parameters, noise correlation, and B1+ maps were assessed. Safety was ensured by numerical simulations using a coil model validated by dosimetric field measurements. RESULTS Meander elements and loops are intrinsically well decoupled with a maximum coupling value of -20.5 dB. Safe use of the 8Tx/32Rx array could be demonstrated. High gain in signal-to-noise ratio (33% in the subject's center) could be shown for the 8Tx/32Rx array compared to the 8Tx/Rx array. Improvement in acceleration capability in all investigations could be demonstrated. For example, the 8Tx/32Rx array provides lower g-factors in the right-left and anterior-posterior directions with R = 3 undersampling as compared to the 8Tx/Rx array using R = 2. Both arrays are very similar regarding their RF transmit performance. Excellent image quality in the investigated body regions could be achieved with the 8Tx/32Rx array. CONCLUSION In this work, we show that a combination of eight meander elements and 24 loop receive elements is possible without impeding transmit performance. Improved SNR and g-factor performance compared to an RF array without these loops is demonstrated. Body MRI at 7T with the 8Tx/32Rx array could be accomplished in the heart, abdomen, and pelvis with excellent image quality.
Collapse
Affiliation(s)
- Stefan H G Rietsch
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, 45147, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany
| | - Sascha Brunheim
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, 45147, Essen, Germany
| | - Bart W J Philips
- Department of Radiology and Nuclear Medicine, Medical Center, Radboud University, 6525GA, Nijmegen, The Netherlands
| | - Tom W J Scheenen
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany.,Department of Radiology and Nuclear Medicine, Medical Center, Radboud University, 6525GA, Nijmegen, The Netherlands
| | - Mark E Ladd
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany.,Medical Physics in Radiology, German Cancer Research Center, 69120, Heidelberg, Germany.,Faculty of Physics and Astronomy and Faculty of Medicine, University of Heidelberg, 69120, Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, 45141, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, 45147, Essen, Germany
| |
Collapse
|
63
|
Laader A, Beiderwellen K, Kraff O, Maderwald S, Ladd ME, Forsting M, Umutlu L. Non-enhanced versus low-dose contrast-enhanced renal magnetic resonance angiography at 7 T: a feasibility study. Acta Radiol 2018; 59:296-304. [PMID: 28691526 DOI: 10.1177/0284185117718399] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Background Considering the currently reported association between a repetitive application and cumulative dosage of Gadolinium (Gd)-based contrast agents and Gd-deposition in brain tissue as well as the risk for the advent of nephrogenic systemic fibrosis (NSF), techniques allowing for a dose reduction become an important key aspect aside from non-enhanced magnetic resonance angiography (MRA) techniques. Thus, this study was focused on the reduction and/or complete omission of contrast agent for renal MRA at 7T. Purpose To evaluate the performance of time-of-flight MRA versus low-dose contrast-enhanced (CE) renal MRA at 7T. Material and Methods Ten healthy volunteers were examined on a 7T MR system comprising a TOF MRA and three-dimensional (3D) fast low angle shot spoiled gradient-echo sequence (FLASH) MRA after administration of one-quarter of clinical dose of gadobutrol. Qualitative image analysis was performed including overall image quality, artery delineation and presence of artifacts. Contrast ratio (CR), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the renal arteries were calculated. Results TOF MRA and low-CE MRA achieved comparable overall ratings, with slightly superior delineation of the main renal arteries in TOF MRA (TOF = 3.10 ± 0.75, low-CE = 2.95 ± 0.75). Segmental branches outside and inside the parenchyma were delineated significantly better on TOF MRA. Quantitative analysis demonstrated the superiority of TOF MRA, yielding higher scores for CR, SNR, and CNR. Conclusion The initial results of our study demonstrate the feasibility and comparable diagnostic performance of TOF and low-dose CE renal MRA at 7T.
Collapse
Affiliation(s)
- Anja Laader
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| | - Karsten Beiderwellen
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| | - Oliver Kraff
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| | - Stefan Maderwald
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| | - Mark E Ladd
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
- German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Michael Forsting
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
- Erwin L Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Essen, Germany
| |
Collapse
|
64
|
Barry RL, Vannesjo SJ, By S, Gore JC, Smith SA. Spinal cord MRI at 7T. Neuroimage 2018; 168:437-451. [PMID: 28684332 PMCID: PMC5894871 DOI: 10.1016/j.neuroimage.2017.07.003] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2016] [Revised: 06/30/2017] [Accepted: 07/02/2017] [Indexed: 11/25/2022] Open
Abstract
Magnetic resonance imaging (MRI) of the human spinal cord at 7T has been demonstrated by a handful of research sites worldwide, and the spinal cord remains one of the areas in which higher fields and resolution could have high impact. The small diameter of the cord (∼1 cm) necessitates high spatial resolution to minimize partial volume effects between gray and white matter, and so MRI of the cord can greatly benefit from increased signal-to-noise ratio and contrasts at ultra-high field (UHF). Herein we review the current state of UHF spinal cord imaging. Technical challenges to successful UHF spinal cord MRI include radiofrequency (B1) nonuniformities and a general lack of optimized radiofrequency coils, amplified physiological noise, and an absence of methods for robust B0 shimming along the cord to mitigate image distortions and signal losses. Numerous solutions to address these challenges have been and are continuing to be explored, and include novel approaches for signal excitation and acquisition, dynamic shimming and specialized shim coils, and acquisitions with increased coverage or optimal slice angulations.
Collapse
Affiliation(s)
- Robert L Barry
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA; Department of Radiology, Harvard Medical School, Boston, MA, USA.
| | - S Johanna Vannesjo
- Oxford Centre for Functional MRI of the Brain (FMRIB), Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Samantha By
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA
| | - John C Gore
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| | - Seth A Smith
- Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Biomedical Engineering, Vanderbilt University, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
| |
Collapse
|
65
|
|
66
|
Uğurbil K. Imaging at ultrahigh magnetic fields: History, challenges, and solutions. Neuroimage 2018; 168:7-32. [PMID: 28698108 PMCID: PMC5758441 DOI: 10.1016/j.neuroimage.2017.07.007] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 07/05/2017] [Accepted: 07/07/2017] [Indexed: 01/06/2023] Open
Abstract
Following early efforts in applying nuclear magnetic resonance (NMR) spectroscopy to study biological processes in intact systems, and particularly since the introduction of 4 T human scanners circa 1990, rapid progress was made in imaging and spectroscopy studies of humans at 4 T and animal models at 9.4 T, leading to the introduction of 7 T and higher magnetic fields for human investigation at about the turn of the century. Work conducted on these platforms has provided numerous technological solutions to challenges posed at these ultrahigh fields, and demonstrated the existence of significant advantages in signal-to-noise ratio and biological information content. Primary difference from lower fields is the deviation from the near field regime at the radiofrequencies (RF) corresponding to hydrogen resonance conditions. At such ultrahigh fields, the RF is characterized by attenuated traveling waves in the human body, which leads to image non-uniformities for a given sample-coil configuration because of destructive and constructive interferences. These non-uniformities were initially considered detrimental to progress of imaging at high field strengths. However, they are advantageous for parallel imaging in signal reception and transmission, two critical technologies that account, to a large extend, for the success of ultrahigh fields. With these technologies and improvements in instrumentation and imaging methods, today ultrahigh fields have provided unprecedented gains in imaging of brain function and anatomy, and started to make inroads into investigation of the human torso and extremities. As extensive as they are, these gains still constitute a prelude to what is to come given the increasingly larger effort committed to ultrahigh field research and development of ever better instrumentation and techniques.
Collapse
Affiliation(s)
- Kamil Uğurbil
- Center for Magnetic Resonance Research (CMRR), University of Minnesota Medical School, Minneapolis, MN 55455, USA.
| |
Collapse
|
67
|
Alon L, Lattanzi R, Lakshmanan K, Brown R, Deniz CM, Sodickson DK, Collins CM. Transverse slot antennas for high field MRI. Magn Reson Med 2018; 80:1233-1242. [PMID: 29388250 PMCID: PMC5985532 DOI: 10.1002/mrm.27095] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Revised: 12/28/2017] [Accepted: 12/28/2017] [Indexed: 11/23/2022]
Abstract
Purpose Introduce a novel coil design using an electrically long transversely oriented slot in a conductive sheet. Theory and Methods Theoretical considerations, numerical simulations, and experimental measurements are presented for transverse slot antennas as compared with electric dipole antennas. Results Simulations show improved central and average transmit and receive efficiency, as well as larger coverage in the transverse plane, for a single slot as compared to a single dipole element. Experiments on a body phantom confirm the simulation results for a slot antenna relative to a dipole, demonstrating a large region of relatively high sensitivity and homogeneity. Images in a human subject also show a large imaging volume for a single slot and six slot antenna array. High central transmit efficiency was observed for slot arrays relative to dipole arrays. Conclusion Transverse slots can exhibit improved sensitivity and larger field of view compared with traditional conductive dipoles. Simulations and experiments indicate high potential for slot antennas in high field MRI. Magn Reson Med 80:1233–1242, 2018. © 2018 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Collapse
Affiliation(s)
- Leeor Alon
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,RF Test Labs, Inc., New York, New York, USA
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA
| | - Karthik Lakshmanan
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA
| | - Ryan Brown
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA
| | - Cem M Deniz
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA.,RF Test Labs, Inc., New York, New York, USA
| | - Daniel K Sodickson
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA
| | - Christopher M Collins
- Center for Advanced Imaging Innovation and Research (CAI2R), and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, New York, USA.,NYU WIRELESS, New York University Tandon School of Engineering, Brooklyn, New York, USA
| |
Collapse
|
68
|
Li X, Auerbach EJ, Van de Moortele PF, Ugurbil K, Metzger GJ. Quantitative single breath-hold renal arterial spin labeling imaging at 7T. Magn Reson Med 2018; 79:815-825. [PMID: 28488274 PMCID: PMC5680158 DOI: 10.1002/mrm.26742] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2016] [Revised: 04/10/2017] [Accepted: 04/11/2017] [Indexed: 12/18/2022]
Abstract
PURPOSE To evaluate the feasibility of quantitative single breath-hold renal arterial spin labeling (ASL) imaging at 7T. METHODS A single-shot fast spin echo FAIR (flow-sensitive alternating inversion recovery) method was used to perform two studies. First, a multi-delay perfusion study was performed to estimate the spin labeling temporal bolus width achievable with a local transceiver array coil at 7T. Second, with a conservatively defined bolus width, a quantitative perfusion study was performed using the single subtraction approach. To address issues of B1+ inhomogeneity/efficiency and excessive short-term specific absorption rates, various strategies were used, such as dynamic radiofrequency shimming and optimization. RESULTS A conservative temporal bolus width of 600 ms determined from the multi-delay study was applied for single-subtraction imaging to measure the renal blood flow in the cortex and medulla: 303 ± 31.8 and 91.3 ± 15.2 (mL/100 g/min), respectively. The estimated spatial and temporal signal-to-noise ratios of renal perfusion measurements were 3.8 ± 0.7 and 2.4 ± 0.6 for the cortex, and 2.2 ± 0.6 and 1.4 ± 0.2 for the medulla. CONCLUSION With proper management of field strength specific challenges, quantitative renal ASL imaging can be achieved at 7T within a single breath-hold. Magn Reson Med 79:815-825, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Xiufeng Li
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, United States
| | - Edward J. Auerbach
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, United States
| | | | - Kamil Ugurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, United States
| | - Gregory J. Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, United States
| |
Collapse
|
69
|
Herrmann T, Liebig T, Mallow J, Bruns C, Stadler J, Mylius J, Brosch M, Svedja JT, Chen Z, Rennings A, Scheich H, Plaumann M, Hauser MJB, Bernarding J, Erni D. Metamaterial-based transmit and receive system for whole-body magnetic resonance imaging at ultra-high magnetic fields. PLoS One 2018; 13:e0191719. [PMID: 29370245 PMCID: PMC5784978 DOI: 10.1371/journal.pone.0191719] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2017] [Accepted: 01/10/2018] [Indexed: 11/24/2022] Open
Abstract
Magnetic resonance imaging (MRI) at ultra-high fields (UHF), such as 7 T, provides an enhanced signal-to-noise ratio and has led to unprecedented high-resolution anatomic images and brain activation maps. Although a variety of radio frequency (RF) coil architectures have been developed for imaging at UHF conditions, they usually are specialized for small volumes of interests (VoI). So far, whole-body coil resonators are not available for commercial UHF human whole-body MRI systems. The goal of the present study was the development and validation of a transmit and receive system for large VoIs that operates at a 7 T human whole-body MRI system. A Metamaterial Ring Antenna System (MRAS) consisting of several ring antennas was developed, since it allows for the imaging of extended VoIs. Furthermore, the MRAS not only requires lower intensities of the irradiated RF energy, but also provides a more confined and focused injection of excitation energy on selected body parts. The MRAS consisted of several antennas with 50 cm inner diameter, 10 cm width and 0.5 cm depth. The position of the rings was freely adjustable. Conformal resonant right-/left-handed metamaterial was used for each ring antenna with two quadrature feeding ports for RF power. The system was successfully implemented and demonstrated with both a silicone oil and a water-NaCl-isopropanol phantom as well as in vivo by acquiring whole-body images of a crab-eating macaque. The potential for future neuroimaging applications was demonstrated by the acquired high-resolution anatomic images of the macaque's head. Phantom and in vivo measurements of crab-eating macaques provided high-resolution images with large VoIs up to 40 cm in xy-direction and 45 cm in z-direction. The results of this work demonstrate the feasibility of the MRAS system for UHF MRI as proof of principle. The MRAS shows a substantial potential for MR imaging of larger volumes at 7 T UHF. This new technique may provide new diagnostic potential in spatially extended pathologies such as searching for spread-out tumor metastases or monitoring systemic inflammatory processes.
Collapse
Affiliation(s)
- Tim Herrmann
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
| | - Thorsten Liebig
- General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany
| | - Johannes Mallow
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
| | - Christian Bruns
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
| | - Jörg Stadler
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
| | - Judith Mylius
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
| | - Michael Brosch
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
- Center for Behavioral Brain Sciences, Magdeburg, Germany
| | - Jan Taro Svedja
- General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany
| | - Zhichao Chen
- General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany
| | - Andreas Rennings
- General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany
| | - Henning Scheich
- Leibniz Institute for Neurobiology (LIN), Magdeburg, Germany
- Center for Behavioral Brain Sciences, Magdeburg, Germany
| | - Markus Plaumann
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
| | - Marcus J B Hauser
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
| | - Johannes Bernarding
- Institute of Biometrics and Medical Informatics, Otto-von-Guericke University Magdeburg, Magdeburg, Germany
- Center for Behavioral Brain Sciences, Magdeburg, Germany
| | - Daniel Erni
- General and Theoretical Electrical Engineering (ATE), University of Duisburg-Essen, and CENIDE-Center for Nanointegration Duisburg-Essen, Duisburg, Germany
| |
Collapse
|
70
|
Paška J, Cloos MA, Wiggins GC. A rigid, stand-off hybrid dipole, and birdcage coil array for 7 T body imaging. Magn Reson Med 2017; 80:822-832. [PMID: 29250833 DOI: 10.1002/mrm.27048] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 10/23/2017] [Accepted: 11/24/2017] [Indexed: 11/11/2022]
Abstract
PURPOSE To design a robust and patient friendly radiofrequency coil array (8-channel transmit and 16-channel receive) for cross-sectional body imaging at 7 T, and to improve our understanding of the combination of dipole and loop like elements for ultra high field strengths. METHODS The hybrid coil array was optimized in eletromagnetic simulations. Considered array candidates were the dipole, loop and birdcage array. The winning design was constructed and the signal-to-noise (SNR) was compared to a close fitting array at 3 T. Transmit and receive properties for different body sizes were assessed, and multi-parametric maps were acquired with the Plug-and-Play MRF method. RESULTS The winning design consists of a dipole array for transceive combined with a birdcage array for receive only. The central SNR improved by a factor of 3 as compared to a 3 T system with a local receive array. A transmit efficiency between 2.4 and 3.9 μT/kW, a specific absorption rate efficiency of 0.25 to 0.53 μT/W/kg, and a high SNR was achieved in the center for the targeted patient population. CONCLUSION The constructed coil array is easy to handle, safe, and patient friendly, allowing further development of abdominal imaging at 7 T. Quantitative MRI in the abdomen is possible with Plug-and-Play MRF using the designed coil array. Magn Reson Med 80:822-832, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Jan Paška
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| | - Martijn A Cloos
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| | - Graham C Wiggins
- Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, New York, New York, USA.,Center for Advanced Imaging Innovation and Research (CAI2R), Department of Radiology, New York University School of Medicine, New York, New York, USA
| |
Collapse
|
71
|
Laader A, Beiderwellen K, Kraff O, Maderwald S, Wrede K, Ladd ME, Lauenstein TC, Forsting M, Quick HH, Nassenstein K, Umutlu L. 1.5 versus 3 versus 7 Tesla in abdominal MRI: A comparative study. PLoS One 2017; 12:e0187528. [PMID: 29125850 PMCID: PMC5695282 DOI: 10.1371/journal.pone.0187528] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Accepted: 10/21/2017] [Indexed: 01/04/2023] Open
Abstract
Objectives The aim of this study was to investigate and compare the feasibility as well as potential impact of altered magnetic field properties on image quality and potential artifacts of 1.5 Tesla, 3 Tesla and 7 Tesla non-enhanced abdominal MRI. Materials and methods Magnetic Resonance (MR) imaging of the upper abdomen was performed in 10 healthy volunteers on a 1.5 Tesla, a 3 Tesla and a 7 Tesla MR system. The study protocol comprised a (1) T1-weighted fat-saturated spoiled gradient-echo sequence (2D FLASH), (2) T1-weighted fat-saturated volumetric interpolated breath hold examination sequence (3D VIBE), (3) T1-weighted 2D in and opposed phase sequence, (4) True fast imaging with steady-state precession sequence (TrueFISP) and (5) T2-weighted turbo spin-echo (TSE) sequence. For comparison reasons field of view and acquisition times were kept comparable for each correlating sequence at all three field strengths, while trying to achieve the highest possible spatial resolution. Qualitative and quantitative analyses were tested for significant differences. Results While 1.5 and 3 Tesla MRI revealed comparable results in all assessed features and sequences, 7 Tesla MRI yielded considerable differences in T1 and T2 weighted imaging. Benefits of 7 Tesla MRI encompassed an increased higher spatial resolution and a non-enhanced hyperintense vessel signal at 7 Tesla, potentially offering a more accurate diagnosis of abdominal parenchymatous and vasculature disease. 7 Tesla MRI was also shown to be more impaired by artifacts, including residual B1 inhomogeneities, susceptibility and chemical shift artifacts, resulting in reduced overall image quality and overall image impairment ratings. While 1.5 and 3 Tesla T2w imaging showed equivalently high image quality, 7 Tesla revealed strong impairments in its diagnostic value. Conclusions Our results demonstrate the feasibility and overall comparable imaging ability of T1-weighted 7 Tesla abdominal MRI towards 3 Tesla and 1.5 Tesla MRI, yielding a promising diagnostic potential for non-enhanced Magnetic Resonance Angiography (MRA). 1.5 Tesla and 3 Tesla offer comparably high-quality T2w imaging, showing superior diagnostic quality over 7 Tesla MRI.
Collapse
Affiliation(s)
- Anja Laader
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
- * E-mail:
| | - Karsten Beiderwellen
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
| | - Oliver Kraff
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
| | - Stefan Maderwald
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
| | - Karsten Wrede
- Department of Neurosurgery, University Hospital Essen, Hufelandstr. 55, Essen, Germany
| | - Mark E. Ladd
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
- German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg, Germany
| | - Thomas C. Lauenstein
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
- Institute of Radiology, Evangelisches Krankenhaus Düsseldorf, Kirchfeldstr. 40, Düsseldorf, Germany
| | - Michael Forsting
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
| | - Harald H. Quick
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
- High Field and Hybrid MR Imaging, University Hospital Essen, Hufelandstr. 55, Essen, Germany
| | - Kai Nassenstein
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
| | - Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Hufelandstr. 55, Essen, Germany
- Erwin L. Hahn Institute for Magnetic Resonance Imaging, University Duisburg-Essen, Kokereiallee 7, Essen, Germany
| |
Collapse
|
72
|
Vaidya MV, Deniz CM, Collins CM, Sodickson DK, Lattanzi R. Manipulating transmit and receive sensitivities of radiofrequency surface coils using shielded and unshielded high-permittivity materials. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2017; 31:355-366. [PMID: 29110240 DOI: 10.1007/s10334-017-0657-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Revised: 09/29/2017] [Accepted: 10/02/2017] [Indexed: 10/18/2022]
Abstract
OBJECTIVE To use high-permittivity materials (HPM) positioned near radiofrequency (RF) surface coils to manipulate transmit/receive field patterns. MATERIALS AND METHODS A large HPM pad was placed below the RF coil to extend the field of view (FOV). The resulting signal-to-noise ratio (SNR) was compared with that of other coil configurations covering the same FOV in simulations and experiments at 7 T. Transmit/receive efficiency was evaluated when HPM discs with or without a partial shield were positioned at a distance from the coil. Finally, we evaluated the increase in transmit homogeneity for a four-channel array with HPM discs interposed between adjacent coil elements. RESULTS Various configurations of HPM increased SNR, transmit/receive efficiency, excitation/reception sensitivity overlap, and FOV when positioned near a surface coil. For a four-channel array driven in quadrature, shielded HPM discs enhanced the field below the discs as well as at the center of the sample as compared with other configurations with or without unshielded HPM discs. CONCLUSION Strategically positioning HPM at a distance from a surface coil or array can increase the overlap between excitation/reception sensitivities, and extend the FOV of a single coil for reduction of the number of channels in an array while minimally affecting the SNR.
Collapse
Affiliation(s)
- Manushka V Vaidya
- Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA. .,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA. .,NYU WIRELESS, 2 Metro Tech Center, Brooklyn, NY, 11201, USA.
| | - Cem M Deniz
- Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA.,NYU WIRELESS, 2 Metro Tech Center, Brooklyn, NY, 11201, USA
| | - Christopher M Collins
- Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA.,NYU WIRELESS, 2 Metro Tech Center, Brooklyn, NY, 11201, USA
| | - Daniel K Sodickson
- Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA.,NYU WIRELESS, 2 Metro Tech Center, Brooklyn, NY, 11201, USA
| | - Riccardo Lattanzi
- Center for Advanced Imaging Innovation and Research and the Bernard and Irene Schwartz Center for Biomedical Imaging, Department of Radiology, New York University School of Medicine, 660 First Ave, Fourth Floor, New York, NY, 10016, USA.,The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, 550 First Avenue, New York, NY, 10016, USA.,NYU WIRELESS, 2 Metro Tech Center, Brooklyn, NY, 11201, USA
| |
Collapse
|
73
|
Winkler SA, Picot PA, Thornton MM, Rutt BK. Direct SAR mapping by thermoacoustic imaging: A feasibility study. Magn Reson Med 2017; 78:1599-1606. [PMID: 27779779 PMCID: PMC5405009 DOI: 10.1002/mrm.26517] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2016] [Revised: 09/01/2016] [Accepted: 09/27/2016] [Indexed: 11/09/2022]
Abstract
PURPOSE To develop a new method capable of directly measuring specific absorption rate (SAR) deposited in tissue using the thermoacoustic signal induced by short radiofrequency (RF) pulse excitation. THEORY A detailed model based on the thermoacoustic wave generation and propagation is presented. METHODS We propose a new concept for direct measurement of SAR, to be used as a safety assessment/monitoring tool for MRI. The concept involves the use of short bursts of RF energy and the measurement of the resulting thermoacoustic excitation pattern by an array of ultrasound transducers, followed by image reconstruction to yield the 3D SAR distribution. We developed a simulation framework to model this thermoacoustic SAR mapping concept and verified the concept in vitro. RESULTS Simulations show good agreement between reconstructed and original SAR distributions with an error of 4.2, 7.2, and 8.4% of the mean SAR values in axial, sagittal, and coronal planes and support the feasibility of direct experimental mapping of SAR distributions in vivo. The in vitro experiments show good agreement with theory (r2 = 0.52). CONCLUSIONS A novel thermoacoustic method for in vivo mapping of local SAR patterns in MRI has been proposed and verified in simulation and in a phantom experiment. Magn Reson Med 78:1599-1606, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Simone A. Winkler
- Department of Radiology, Stanford University, Stanford, California, USA
| | | | | | - Brian K. Rutt
- Department of Radiology, Stanford University, Stanford, California, USA
| |
Collapse
|
74
|
Ipek Ö. Radio-frequency coils for ultra-high field magnetic resonance. Anal Biochem 2017; 529:10-16. [DOI: 10.1016/j.ab.2017.03.022] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 03/24/2017] [Accepted: 03/27/2017] [Indexed: 10/19/2022]
|
75
|
Raval SB, Britton CA, Zhao T, Krishnamurthy N, Santini T, Gorantla VS, Ibrahim TS. Ultra-high field upper extremity peripheral nerve and non-contrast enhanced vascular imaging. PLoS One 2017; 12:e0175629. [PMID: 28662061 PMCID: PMC5490941 DOI: 10.1371/journal.pone.0175629] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2016] [Accepted: 03/29/2017] [Indexed: 01/05/2023] Open
Abstract
OBJECTIVE The purpose of this study was to explore the efficacy of Ultra-high field [UHF] 7 Tesla [T] MRI as compared to 3T MRI in non-contrast enhanced [nCE] imaging of structural anatomy in the elbow, forearm, and hand [upper extremity]. MATERIALS AND METHOD A wide range of sequences including T1 weighted [T1] volumetric interpolate breath-hold exam [VIBE], T2 weighted [T2] double-echo steady state [DESS], susceptibility weighted imaging [SWI], time-of-flight [TOF], diffusion tensor imaging [DTI], and diffusion spectrum imaging [DSI] were optimized and incorporated with a radiofrequency [RF] coil system composed of a transverse electromagnetic [TEM] transmit coil combined with an 8-channel receive-only array for 7T upper extremity [UE] imaging. In addition, Siemens optimized protocol/sequences were used on a 3T scanner and the resulting images from T1 VIBE and T2 DESS were compared to that obtained at 7T qualitatively and quantitatively [SWI was only qualitatively compared]. DSI studio was utilized to identify nerves based on analysis of diffusion weighted derived fractional anisotropy images. Images of forearm vasculature were extracted using a paint grow manual segmentation method based on MIPAV [Medical Image Processing, Analysis, and Visualization]. RESULTS High resolution and high quality signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]-images of the hand, forearm, and elbow were acquired with nearly homogeneous 7T excitation. Measured [performed on the T1 VIBE and T2 DESS sequences] SNR and CNR values were almost doubled at 7T vs. 3T. Cartilage, synovial fluid and tendon structures could be seen with higher clarity in the 7T T1 and T2 weighted images. SWI allowed high resolution and better quality imaging of large and medium sized arteries and veins, capillary networks and arteriovenous anastomoses at 7T when compared to 3T. 7T diffusion weighted sequence [not performed at 3T] demonstrates that the forearm nerves are clearly delineated by fiber tractography. The proper digital palmar arteries and superficial palmar arch could also be clearly visualized using TOF nCE 7T MRI. CONCLUSION Ultra-high resolution neurovascular imaging in upper extremities is possible at 7T without use of renal toxic intravenous contrast. 7T MRI can provide superior peripheral nerve [based on fiber anisotropy and diffusion coefficient parameters derived from diffusion tensor/spectrum imaging] and vascular [nCE MRA and vessel segmentation] imaging.
Collapse
Affiliation(s)
- Shailesh B. Raval
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
| | - Cynthia A. Britton
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
| | - Tiejun Zhao
- Siemens Medical Solutions, New York, United States of America
| | - Narayanan Krishnamurthy
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
| | - Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
| | - Vijay S. Gorantla
- Department of Plastic Surgery, Pittsburgh, Pittsburgh, United States of America
- * E-mail: (TSI); (VSG)
| | - Tamer S. Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pittsburgh, United States of America
- * E-mail: (TSI); (VSG)
| |
Collapse
|
76
|
O'Reilly TPA, Ruytenberg T, Webb AG. Modular transmit/receive arrays using very-high permittivity dielectric resonator antennas. Magn Reson Med 2017. [PMID: 28635034 PMCID: PMC5811774 DOI: 10.1002/mrm.26784] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PURPOSE Dielectric resonator antenna (DRAs) are compact structures that exhibit low coupling between adjacent elements and therefore can be used as MRI transmit arrays. In this study, we use very high permittivity materials to construct modular flexible transceive arrays of a variable numbers of elements for operation at 7T. METHODS DRAs were constructed using rectangular blocks of ceramic (lead zirconate titanate, εr = 1070) with the transverse electric (TE)01 mode tuned to 298 MHz. Finite-difference time-domain simulations were used to determine the B1 and specific absorption rate distributions. B1+ maps were acquired in a phantom to validate the simulations. Performance was compared to an equally sized surface coil. In vivo images were acquired of the wrist (four elements), ankle (seven elements), and calf muscle (16 elements). RESULTS Coupling between DRAs spaced 5 mm apart on a phantom was -18.2 dB compared to -9.1 dB for equivalently spaced surface coils. DRAs showed a higher B1+ intensity close to the antenna but a lower penetration depth compared to the surface coil. CONCLUSION DRAs show very low coupling compared to equally sized surface coils and can be used in transceive arrays without requiring decoupling networks. The penetration depth of the current DRA geometry means they are ideally suited to imaging of extremities. Magn Reson Med 79:1781-1788, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Collapse
Affiliation(s)
- Thomas P A O'Reilly
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Thomas Ruytenberg
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - Andrew G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| |
Collapse
|
77
|
Chen Z, Solbach K, Erni D, Rennings A. Field Distribution and Coupling Investigation of an Eight-Channel RF Coil Consisting of Different Dipole Coil Elements for 7 T MRI. IEEE Trans Biomed Eng 2017; 64:1297-1304. [DOI: 10.1109/tbme.2016.2602441] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
78
|
Buonincontri G, Schulte RF, Cosottini M, Tosetti M. Spiral MR fingerprinting at 7T with simultaneous B1 estimation. Magn Reson Imaging 2017; 41:1-6. [PMID: 28414052 DOI: 10.1016/j.mri.2017.04.003] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 04/11/2017] [Accepted: 04/11/2017] [Indexed: 11/29/2022]
Abstract
Magnetic resonance fingerprinting is an efficient, new approach for quantitative imaging with MR. We aimed to extend this technique to cases with B1+ inhomogeneities within the imaging volume. Previous approaches have used abrupt changes in flip angles to estimate the B1+ field simultaneously with T1 and T2, using a Cartesian approach in a small-animal scanner at 4.7T. Here, we evaluated whether a similar approach would be suitable for imaging human brains using spiral readouts with a 7T scanner. We found that our modified scheme could significantly reduce the adverse effects of B1+ inhomogeneities even in extreme cases, reducing both the bias and the variance in T2 estimations by an order of magnitude when compared to literature methods. Acquisitions used less than 1.5W/kg SAR and could be performed in 12s per slice. In conclusion, our approach can be used to perform quantitative imaging of the brain at 7T in a short time, simultaneously estimating the B1+ profile.
Collapse
Affiliation(s)
| | | | - Mirco Cosottini
- Department of Translational Research and New Technologies in Medicine and Surgery, University of Pisa, Pisa, Italy; IMAGO7 Foundation, Pisa, Italy
| | - Michela Tosetti
- IRCCS Stella Maris Foundation, Pisa, Italy; IMAGO7 Foundation, Pisa, Italy
| |
Collapse
|
79
|
Rietsch SHG, Orzada S, Bitz AK, Gratz M, Ladd ME, Quick HH. Parallel transmit capability of various RF transmit elements and arrays at 7T MRI. Magn Reson Med 2017; 79:1116-1126. [PMID: 28394080 DOI: 10.1002/mrm.26704] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 02/13/2017] [Accepted: 03/16/2017] [Indexed: 12/28/2022]
Abstract
PURPOSE In this work, 22 configurations for remote radiofrequency (RF) coil arrays consisting of different transmit element designs for 7 Tesla (T) ultrahigh-field MRI are compared by numerical simulations. METHODS Investigated transmit RF element types are rectangular loops, micro striplines, micro striplines with meanders, 250-mm shielded dipoles with meanders, and lambda over two dipoles with and without shield. These elements are combined in four different configurations of circumferential RF body arrays with four or eight transmit elements each. Comparisons included coupling behavior, degrees of freedom offered by the individual transmit patterns, and metrics like power and specific absorption rate efficiency. RESULTS Coupling between neighboring RF elements is elevated (up to -7 dB) for all arrays with eight elements, whereas it is below -25 dB for arrays with only four elements. The cumulative sum of singular values points out highest degrees of freedom for the central transversal, reduced values in the central coronal, and minimum values in the sagittal slice. Concerning power and SAR efficiency, eight lambda over two dipoles are most advantageous. CONCLUSIONS Among the investigated remote arrays and parameters, a combination of eight dipoles appears to be most favorable for potential use in 7T body MRI. Magn Reson Med 79:1116-1126, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- Stefan H G Rietsch
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany
| | - Andreas K Bitz
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Electromagnetic Theory and Applied Mathematics, Faculty of Electrical Engineering and Information Technology, University of Applied Sciences Aachen, Aachen, Germany
| | - Marcel Gratz
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| | - Mark E Ladd
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen, Germany.,High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany
| |
Collapse
|
80
|
O'Reilly TPA, Webb AG, Brink WM. Practical improvements in the design of high permittivity pads for dielectric shimming in neuroimaging at 7T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 270:108-114. [PMID: 27434779 DOI: 10.1016/j.jmr.2016.07.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 06/15/2016] [Accepted: 07/08/2016] [Indexed: 06/06/2023]
Abstract
Improvements are proposed for practical design and use of high permittivity materials in high field neuroimaging in three different areas: (i) a simple formula to predict the permittivity of tri-component aqueous-based perovskite suspensions with relative permittivities between 110 and 300, (ii) characterization of addition of a hydroxyethyl-cellulose gelling agent to improve the long-term stability and material properties of "dielectric pads", and (iii) investigation of the integration of, for example, headphones into the dielectric pads to increase patient comfort within tightly-fitting receive coil arrays.
Collapse
Affiliation(s)
- T P A O'Reilly
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
| | - A G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands.
| | - W M Brink
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands
| |
Collapse
|
81
|
Webb AG, Van de Moortele PF. The technological future of 7 T MRI hardware. NMR IN BIOMEDICINE 2016; 29:1305-1315. [PMID: 25974894 DOI: 10.1002/nbm.3315] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 02/07/2015] [Accepted: 04/07/2015] [Indexed: 06/04/2023]
Abstract
In this article we present our projections of future hardware developments on 7 T human MRI systems. These include compact cryogen-light magnets, improved gradient performance, integrated RF-receive and direct current shimming coil arrays, new RF technology with adaptive impedance matching, patient-specific specific absorption rate estimation and monitoring, and increased integration of physiological monitoring systems. Copyright © 2015 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- A G Webb
- C. J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
| | - P F Van de Moortele
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota Medical School, Minneapolis, MN, USA
| |
Collapse
|
82
|
Raaijmakers AJE, Luijten PR, van den Berg CAT. Dipole antennas for ultrahigh-field body imaging: a comparison with loop coils. NMR IN BIOMEDICINE 2016; 29:1122-1130. [PMID: 26278544 DOI: 10.1002/nbm.3356] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Revised: 04/10/2015] [Accepted: 06/08/2015] [Indexed: 06/04/2023]
Abstract
Although the potential of dipole antennas for ultrahigh-field (UHF) MRI is largely recognized, they are still relatively unknown to the larger part of the MRI community. This article intends to provide electromagnetic insight into the general operating principles of dipole antennas by numerical simulations. The major part focuses on a comparison study of dipole antennas and loop coils at frequencies of 128, 298 and 400 MHz. This study shows that dipole antennas are only efficient radiofrequency (RF) coils in the presence of a dielectric and/or conducting load. In addition, the conservative electric fields (E-fields) at the ends of a dipole are negligible in comparison with the induced E-fields in the center. Like loop coils, long dipole antennas perform better than short dipoles for deeply located imaging targets and vice versa. When the optimal element is chosen for each depth, loop coils have higher B1 (+) efficiency for shallow depths, whereas dipole antennas have higher B1 (+) efficiency for large depths. The cross-over point depth decreases with increasing frequency: 11.6, 6.2 and 5.0 cm for 128, 298 and 400 MHz, respectively. For single elements, loop coils demonstrate a better B1 (+) /√SARmax ratio for any target depth and any frequency. However, one example study shows that, in an array setup with loop coil overlap for decoupling, this relationship is not straightforward. The overlapping loop coils may generate increased specific absorption rate (SAR) levels under the overlapping parts of the loops, depending on the drive phase settings. Copyright © 2015 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
| | - P R Luijten
- UMC Utrecht, Department of Radiology, Utrecht, the Netherlands
| | | |
Collapse
|
83
|
Niendorf T, Paul K, Oezerdem C, Graessl A, Klix S, Huelnhagen T, Hezel F, Rieger J, Waiczies H, Frahm J, Nagel AM, Oberacker E, Winter L. W(h)ither human cardiac and body magnetic resonance at ultrahigh fields? technical advances, practical considerations, applications, and clinical opportunities. NMR IN BIOMEDICINE 2016; 29:1173-97. [PMID: 25706103 DOI: 10.1002/nbm.3268] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 12/26/2014] [Accepted: 01/13/2015] [Indexed: 05/12/2023]
Abstract
The objective of this study was to document and review advances and groundbreaking progress in cardiac and body MR at ultrahigh fields (UHF, B0 ≥ 7.0 T) with the goal to attract talent, clinical adopters, collaborations and resources to the biomedical and diagnostic imaging communities. This review surveys traits, advantages and challenges of cardiac and body MR at 7.0 T. The considerations run the gamut from technical advances to clinical opportunities. Key concepts, emerging technologies, practical considerations, frontier applications and future directions of UHF body and cardiac MR are provided. Examples of UHF cardiac and body imaging strategies are demonstrated. Their added value over the kindred counterparts at lower fields is explored along with an outline of research promises. The achievements of cardiac and body UHF-MR are powerful motivators and enablers, since extra speed, signal and imaging capabilities may be invested to overcome the fundamental constraints that continue to hamper traditional cardiac and body MR applications. If practical obstacles, concomitant physics effects and technical impediments can be overcome in equal measure, sophisticated cardiac and body UHF-MR will help to open the door to new MRI and MRS approaches for basic research and clinical science, with the lessons learned at 7.0 T being transferred into broad clinical use including diagnostics and therapy guiding at lower fields. Copyright © 2015 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Berlin, Germany
| | - Katharina Paul
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Celal Oezerdem
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Andreas Graessl
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Sabrina Klix
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Till Huelnhagen
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Fabian Hezel
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | | | | | - Jens Frahm
- Biomedizinische NMR Forschungs GmbH, am Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
- DZHK (German Centre for Cardiovascular Research), Partner Site, Göttingen, Germany
| | - Armin M Nagel
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Eva Oberacker
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Lukas Winter
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrueck Center for Molecular Medicine, Berlin, Germany
| |
Collapse
|
84
|
Kim J, Krishnamurthy N, Santini T, Zhao Y, Zhao T, Bae KT, Ibrahim TS. Experimental and numerical analysis of B1(+) field and SAR with a new transmit array design for 7T breast MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 269:55-64. [PMID: 27240143 PMCID: PMC4979605 DOI: 10.1016/j.jmr.2016.04.012] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 04/20/2016] [Accepted: 04/21/2016] [Indexed: 05/15/2023]
Abstract
Developing a radiofrequency (RF) coil system that produces a uniform B1(+) field (circularly polarized component of the transverse magnetic field responsible for excitation) and low specific absorption rate (SAR) is critical for high performance ultrahigh field human imaging. In this study, we provide the design of a new eight channel radiofrequency (RF) transmit (Tx) array for breast MRI at 7T. A numerical analysis utilizing an in-house finite difference time domain (FDTD) package was carried out in (1) four breast models, (2) homogeneous spherical model and (3) full body model to calculate the B1(+) intensity (μT) and homogeneity represented by coefficient of variation (CoV=standard deviation/mean) in the proposed RF array design. The numerical results were compared with that measured in breast phantom (Bphantom) and homogeneous spherical phantom at 7T MRI and showed very good agreement. Average and peak SARs were also calculated in the four breast models and the temperature rises due to the operation of the RF array were also measured in the Bphantom. The proposed RF array; which can operate in a single or multi transmit modes, demonstrates homogeneous RF field excitation with acceptable local/average SAR levels for breast MRI at 7T.
Collapse
Affiliation(s)
- Junghwan Kim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | | | - Tales Santini
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Yujuan Zhao
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Tiejun Zhao
- MR Research Support, Siemens Healthcare, Pittsburgh, PA 15213, USA
| | - Kyongtae Ty Bae
- Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213, USA; Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Tamer S Ibrahim
- Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15261, USA; Department of Radiology, University of Pittsburgh, Pittsburgh, PA 15213, USA.
| |
Collapse
|
85
|
Hurshkainen AA, Derzhavskaya TA, Glybovski SB, Voogt IJ, Melchakova IV, van den Berg CAT, Raaijmakers AJE. Element decoupling of 7T dipole body arrays by EBG metasurface structures: Experimental verification. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 269:87-96. [PMID: 27262656 DOI: 10.1016/j.jmr.2016.05.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Revised: 05/07/2016] [Accepted: 05/25/2016] [Indexed: 06/05/2023]
Abstract
Metasurfaces are artificial electromagnetic boundaries or interfaces usually implemented as two-dimensional periodic structures with subwavelength periodicity and engineered properties of constituent unit cells. The electromagnetic bandgap (EBG) effect in metasurfaces prevents all surface modes from propagating in a certain frequency band. While metasurfaces provide a number of important applications in microwave antennas and antenna arrays, their features are also highly suitable for MRI applications. In this work we perform a proof-of-principle experiment to study finite structures based on mushroom-type EBG metasurfaces and employ them for suppression of inter-element coupling in dipole transceive array coils for body imaging at 7T. We firstly show experimentally that employment of mushroom structures leads to reduction of coupling between adjacent closely-spaced dipole antenna elements of a 7T transceive body array, which reduces scattering losses in neighboring channels. The studied setup consists of two active fractionated dipole antennas previously designed by the authors for body imaging at 7T. These are placed on top of a body-mimicking phantom and equipped with the manufactured finite-size periodic structure tuned to have EBG properties at the Larmor frequency of 298MHz. To improve the detection range of the B1+ field distribution of the top elements, four additional elements were positioned along the bottom side of the phantom. Bench measurements of a scattering matrix showed that coupling between the two top elements can be considerably reduced depending on the distance to the EBG structure. On the other hand, the measurements performed on a 7T MRI machine indicated redistribution of the B1+ field due to interaction between the dipoles with the structure. When the structure is located just over two closely spaced dipoles, one can reach a very high isolation improvement of -14dB accompanied by a strong field redistribution. In contrast, when put at a certain height over the antennas the structure provides a moderate isolation improvement together with a slight increase of B1+ level. This study provides a tool for the decoupling of dipole antennas in ultrahigh field transceive arrays, possibly resulting in denser element placement and/or larger subject-element spacing.
Collapse
Affiliation(s)
- Anna A Hurshkainen
- Department of Nanophotonics and Metamaterials, ITMO University, 197101 St. Petersburg, Russia.
| | - Tatyana A Derzhavskaya
- Department of Nanophotonics and Metamaterials, ITMO University, 197101 St. Petersburg, Russia.
| | - Stanislav B Glybovski
- Department of Nanophotonics and Metamaterials, ITMO University, 197101 St. Petersburg, Russia.
| | - Ingmar J Voogt
- University Medical Center Utrecht, 3584 CX, Netherlands.
| | - Irina V Melchakova
- Department of Nanophotonics and Metamaterials, ITMO University, 197101 St. Petersburg, Russia.
| | | | | |
Collapse
|
86
|
Budinger TF, Bird MD, Frydman L, Long JR, Mareci TH, Rooney WD, Rosen B, Schenck JF, Schepkin VD, Sherry AD, Sodickson DK, Springer CS, Thulborn KR, Uğurbil K, Wald LL. Toward 20 T magnetic resonance for human brain studies: opportunities for discovery and neuroscience rationale. MAGMA (NEW YORK, N.Y.) 2016; 29:617-39. [PMID: 27194154 PMCID: PMC5538368 DOI: 10.1007/s10334-016-0561-4] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Revised: 04/06/2016] [Accepted: 04/11/2016] [Indexed: 12/16/2022]
Abstract
An initiative to design and build magnetic resonance imaging (MRI) and spectroscopy (MRS) instruments at 14 T and beyond to 20 T has been underway since 2012. This initiative has been supported by 22 interested participants from the USA and Europe, of which 15 are authors of this review. Advances in high temperature superconductor materials, advances in cryocooling engineering, prospects for non-persistent mode stable magnets, and experiences gained from large-bore, high-field magnet engineering for the nuclear fusion endeavors support the feasibility of a human brain MRI and MRS system with 1 ppm homogeneity over at least a 16-cm diameter volume and a bore size of 68 cm. Twelve neuroscience opportunities are presented as well as an analysis of the biophysical and physiological effects to be investigated before exposing human subjects to the high fields of 14 T and beyond.
Collapse
Affiliation(s)
- Thomas F Budinger
- Lawrence Berkeley National Laboratory, University of California, Berkeley, CA, USA.
| | - Mark D Bird
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Lucio Frydman
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
- Weizmann Institute, Rehovot, Israel
| | - Joanna R Long
- McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | - Thomas H Mareci
- McKnight Brain Institute, University of Florida, Gainesville, FL, USA
| | | | - Bruce Rosen
- Massachusetts General Hospital, Harvard Medical School, Harvard, MA, USA
| | - John F Schenck
- General Electric Corporate Research, Schenectady, NY, USA
| | - Victor D Schepkin
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - A Dean Sherry
- University of Texas Southwestern Medical Center, Dallas, TX, USA
| | | | | | | | | | - Lawrence L Wald
- Massachusetts General Hospital, Harvard Medical School, Harvard, MA, USA
| |
Collapse
|
87
|
Rietsch SHG, Quick HH, Orzada S. Impact of different meander sizes on the RF transmit performance and coupling of microstrip line elements at 7 T. Med Phys 2016; 42:4542-52. [PMID: 26233183 DOI: 10.1118/1.4923177] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE In this work, the transmit performance and interelement coupling characteristics of radio frequency (RF) antenna microstrip line elements are examined in simulations and measurements. METHODS The initial point of the simulations is a microstrip line element loaded with a phantom. Meander structures are then introduced at the end of the element. The size of the meanders is increased in fixed steps and the magnetic field is optimized. In continuative simulations, the coupling between identical elements is evaluated for different element spacing and loading conditions. Verification of the simulation results is accomplished in measurements of the coupling between two identical elements for four different meander sizes. Image acquisition on a 7 T magnetic resonance imaging (MRI) system provides qualitative and quantitative comparisons to confirm the simulation results. RESULTS Simulations point out an optimum range of meander sizes concerning coupling in all chosen geometric setups. Coupling measurement results are in good agreement with the simulations. Qualitative and quantitative comparisons of the acquired MRI images substantiate the coupling results. CONCLUSIONS The coupling between coil elements in RF antenna arrays consisting of the investigated element types can be optimized under consideration of the central magnetic field strength or efficiency depending on the desired application.
Collapse
Affiliation(s)
- Stefan H G Rietsch
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen 45141, Germany and High Field and Hybrid MR Imaging, University Hospital Essen, Essen 45147, Germany
| | - Harald H Quick
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen 45141, Germany and High Field and Hybrid MR Imaging, University Hospital Essen, Essen 45147, Germany
| | - Stephan Orzada
- Erwin L. Hahn Institute for MR Imaging, University of Duisburg-Essen, Essen 45141, Germany
| |
Collapse
|
88
|
Electrodynamics and radiofrequency antenna concepts for human magnetic resonance at 23.5 T (1 GHz) and beyond. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:641-56. [PMID: 27097905 DOI: 10.1007/s10334-016-0559-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2015] [Revised: 04/04/2016] [Accepted: 04/06/2016] [Indexed: 10/21/2022]
Abstract
OBJECTIVE This work investigates electrodynamic constraints, explores RF antenna concepts and examines the transmission fields (B 1 (+) ) and RF power deposition of dipole antenna arrays for (1)H magnetic resonance of the human brain at 1 GHz (23.5 T). MATERIALS AND METHODS Electromagnetic field (EMF) simulations are performed in phantoms with average tissue simulants for dipole antennae using discrete frequencies [300 MHz (7.0 T) to 3 GHz (70.0 T)]. To advance to a human setup EMF simulations are conducted in anatomical human voxel models of the human head using a 20-element dipole array operating at 1 GHz. RESULTS Our results demonstrate that transmission fields suitable for (1)H MR of the human brain can be achieved at 1 GHz. An increase in transmit channel density around the human head helps to enhance B 1 (+) in the center of the brain. The calculated relative increase in specific absorption rate at 23.5 versus 7.0 T was below 1.4 (in-phase phase setting) and 2.7 (circular polarized phase setting) for the dipole antennae array. CONCLUSION The benefits of multi-channel dipole antennae at higher frequencies render MR at 23.5 T feasible from an electrodynamic standpoint. This very preliminary finding opens the door on further explorations that might be catalyzed into a 20-T class human MR system.
Collapse
|
89
|
de Boer A, Hoogduin JM, Blankestijn PJ, Li X, Luijten PR, Metzger GJ, Raaijmakers AJE, Umutlu L, Visser F, Leiner T. 7 T renal MRI: challenges and promises. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2016; 29:417-33. [PMID: 27008461 PMCID: PMC4891364 DOI: 10.1007/s10334-016-0538-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Revised: 02/02/2016] [Accepted: 02/15/2016] [Indexed: 01/07/2023]
Abstract
The progression to 7 Tesla (7 T) magnetic resonance imaging (MRI) yields promises of substantial increase in signal-to-noise (SNR) ratio. This increase can be traded off to increase image spatial resolution or to decrease acquisition time. However, renal 7 T MRI remains challenging due to inhomogeneity of the radiofrequency field and due to specific absorption rate (SAR) constraints. A number of studies has been published in the field of renal 7 T imaging. While the focus initially was on anatomic imaging and renal MR angiography, later studies have explored renal functional imaging. Although anatomic imaging remains somewhat limited by inhomogeneous excitation and SAR constraints, functional imaging results are promising. The increased SNR at 7 T has been particularly advantageous for blood oxygen level-dependent and arterial spin labelling MRI, as well as sodium MR imaging, thanks to changes in field-strength-dependent magnetic properties. Here, we provide an overview of the currently available literature on renal 7 T MRI. In addition, we provide a brief overview of challenges and opportunities in renal 7 T MR imaging.
Collapse
Affiliation(s)
- Anneloes de Boer
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Johannes M Hoogduin
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands.
| | - Peter J Blankestijn
- Department of Nephrology, University Medical Centre Utrecht, Utrecht, The Netherlands
| | - Xiufeng Li
- Department of Radiology, Centre for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Peter R Luijten
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Gregory J Metzger
- Department of Radiology, Centre for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, MN, USA
| | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| | - Lale Umutlu
- Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, Essen, Germany
| | - Fredy Visser
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands.,Philips Healthcare, Best, The Netherlands
| | - Tim Leiner
- Department of Radiology, University Medical Centre Utrecht, Post box 85500, 3508 GA, Utrecht, The Netherlands
| |
Collapse
|
90
|
Raaijmakers AJ, Italiaander M, Voogt IJ, Luijten PR, Hoogduin JM, Klomp DW, van den Berg CA. The fractionated dipole antenna: A new antenna for body imaging at 7
T
esla. Magn Reson Med 2016; 75:1366-74. [DOI: 10.1002/mrm.25596] [Citation(s) in RCA: 143] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2014] [Revised: 12/09/2014] [Accepted: 12/10/2014] [Indexed: 11/11/2022]
|
91
|
Ertürk MA, Raaijmakers AJE, Adriany G, Uğurbil K, Metzger GJ. A 16-channel combined loop-dipole transceiver array for 7 Tesla body MRI. Magn Reson Med 2016; 77:884-894. [PMID: 26887533 DOI: 10.1002/mrm.26153] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 12/21/2015] [Accepted: 01/17/2016] [Indexed: 12/17/2022]
Abstract
PURPOSE To develop a 16-channel transceive body imaging array at 7.0 T with improved transmit, receive, and specific absorption rate (SAR) performance by combining both loop and dipole elements and using their respective and complementary near and far field characteristics. METHODS A 16-channel radiofrequency (RF) coil array consisting of eight loop-dipole blocks (16LD) was designed and constructed. Transmit and receive performance was quantitatively investigated in phantom and human model simulations, and experiments on five healthy volunteers inside the prostate. Comparisons were made with 16-channel microstrip line (16ML) and 10-channel fractionated dipole antenna (10DA) arrays. The 16LD was used to acquire anatomic and functional images of the prostate, kidneys, and heart. RESULTS The 16LD provided > 14% improvements in the signal-to-noise ratio (SNR), peak B1+, B1+ transmit, and SAR efficiencies over the 16ML and 10DA in simulations inside the prostate. Experimentally, the 16LD had > 20% higher SNR and B1+ transmit efficiency compared with other arrays, and achieved up to 51.8% higher peak B1+ compared with 10DA. CONCLUSION Combining loop and dipole elements provided a body imaging array with high channel count and density while limiting inter-element coupling. The 16LD improved both near and far-field performance compared with existing 7.0T body arrays and provided high-quality MRI of the prostate kidneys and heart. Magn Reson Med 77:884-894, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
Collapse
Affiliation(s)
- M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| |
Collapse
|
92
|
Schmitter S, Schnell S, Uğurbil K, Markl M, Van de Moortele PF. Towards high-resolution 4D flow MRI in the human aorta using kt-GRAPPA and B1+ shimming at 7T. J Magn Reson Imaging 2016; 44:486-99. [PMID: 26841070 DOI: 10.1002/jmri.25164] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2015] [Accepted: 01/05/2016] [Indexed: 01/27/2023] Open
Abstract
PURPOSE To evaluate the feasibility of aortic 4D flow magnetic resonance imaging (MRI) at 7T with improved spatial resolution using kt-GRAPPA acceleration while restricting acquisition time and to address radiofrequency (RF) excitation heterogeneities with B1+ shimming. MATERIALS AND METHODS 4D flow MRI data were obtained in the aorta of eight subjects using a 16-channel transmit/receive coil array at 7T. Flow quantification and acquisition time were compared for a kt-GRAPPA accelerated (R = 5) and a standard GRAPPA (R = 2) accelerated protocol. The impact of different dynamic B1+ shimming strategies on flow quantification was investigated. Two kt-GRAPPA accelerated protocols with 1.2 × 1.2 × 1.2 mm(3) and 1.8 × 1.8 × 2.4 mm(3) spatial resolution were compared. RESULTS Using kt-GRAPPA, we achieved a 4.3-fold reduction in net acquisition time resulting in scan times of about 10 minutes. No significant effect on flow quantification was observed compared to standard GRAPPA with R = 2. Optimizing the B1+ fields for the aorta impacted significantly (P < 0.05) the flow quantification while specific B1+ settings were required for respiration navigators. The high-resolution protocol yielded similar flow quantification, but allowed the depiction of branching vessels. CONCLUSION 7T in combination with B1+ shimming allows for high-resolution 4D flow MRI acquisitions in the human aorta, while kt-GRAPPA limits total scan times without affecting flow quantification. J. Magn. Reson. Imaging 2016;44:486-499.
Collapse
Affiliation(s)
- Sebastian Schmitter
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Susanne Schnell
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Kâmil Uğurbil
- Center for Magnetic Resonance Research, Department of Radiology, University of Minnesota, Minneapolis, Minnesota, USA
| | - Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
- Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, Illinois, USA
| | | |
Collapse
|
93
|
Vaidya MV, Collins CM, Sodickson DK, Brown R, Wiggins GC, Lattanzi R. Dependence of B1+ and B1- Field Patterns of Surface Coils on the Electrical Properties of the Sample and the MR Operating Frequency. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2016; 46:25-40. [PMID: 27795697 PMCID: PMC5082994 DOI: 10.1002/cmr.b.21319] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
In high field MRI, the spatial distribution of the radiofrequency magnetic ( B1) field is usually affected by the presence of the sample. For hardware design and to aid interpretation of experimental results, it is important both to anticipate and to accurately simulate the behavior of these fields. Fields generated by a radiofrequency surface coil were simulated using dyadic Green's functions, or experimentally measured over a range of frequencies inside an object whose electrical properties were varied to illustrate a variety of transmit [Formula: see text] and receive [Formula: see text] field patterns. In this work, we examine how changes in polarization of the field and interference of propagating waves in an object can affect the B1 spatial distribution. Results are explained conceptually using Maxwell's equations and intuitive illustrations. We demonstrate that the electrical conductivity alters the spatial distribution of distinct polarized components of the field, causing "twisted" transmit and receive field patterns, and asymmetries between [Formula: see text] and [Formula: see text]. Additionally, interference patterns due to wavelength effects are observed at high field in samples with high relative permittivity and near-zero conductivity, but are not present in lossy samples due to the attenuation of propagating EM fields. This work provides a conceptual framework for understanding B1 spatial distributions for surface coils and can provide guidance for RF engineers.
Collapse
Affiliation(s)
- Manushka V Vaidya
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Christopher M Collins
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Daniel K Sodickson
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Ryan Brown
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| | - Graham C Wiggins
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAI R) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016
| | - Riccardo Lattanzi
- Department of Radiology, Center for Advanced Imaging Innovation and Research (CAIR) and Bernard and Irene Schwartz Center for Biomedical Imaging, New York University School of Medicine, New York, NY 10016; The Sackler Institute of Graduate Biomedical Sciences, New York University School of Medicine, New York, NY 10016; NYU WIRELESS, Polytechnic Institute of New York University, Brooklyn, NY 11201
| |
Collapse
|
94
|
Webb AG, Aussenhofer SA. Evaluation of plasma-based transmit coils for magnetic resonance. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2015; 261:49-53. [PMID: 26529202 DOI: 10.1016/j.jmr.2015.09.012] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 09/22/2015] [Accepted: 09/23/2015] [Indexed: 06/05/2023]
Abstract
In this work a new concept for designing transmit coils for magnetic resonance using a plasma is introduced. Unlike conventional coils, a plasma can be turned on and off, eliminating electrical interactions between coils, and enabling radiofrequency-invisibility when desired. A surfatron has been designed to produce a surface-mode wave which propagates along the inner surface of a commercial fluorescent lighting tube. NMR spectra and images have been produced using the plasma as the transmit coil and a copper-based monopole to receive the signal. The transmit efficiency of the plasma tube was estimated, and is currently much lower than that of an equivalently-sized metal-based structure: however, there are many potential methods for increasing the efficiency using a custom-built plasma tube.
Collapse
Affiliation(s)
- A G Webb
- C.J. Gorter Center for High Field MRI, Leiden University Medical Center, The Netherlands.
| | - S A Aussenhofer
- C.J. Gorter Center for High Field MRI, Leiden University Medical Center, The Netherlands; NORAS MRI products GmbH, Leibnizstrasse 4, 97204 Hoechberg, Germany
| |
Collapse
|
95
|
Ertürk MA, Tian J, Van de Moortele PF, Adriany G, Metzger GJ. Development and evaluation of a multichannel endorectal RF coil for prostate MRI at 7T in combination with an external surface array. J Magn Reson Imaging 2015; 43:1279-87. [PMID: 26584144 DOI: 10.1002/jmri.25099] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Revised: 09/18/2015] [Accepted: 09/21/2015] [Indexed: 11/05/2022] Open
Abstract
PURPOSE To develop and evaluate a sterilizable multichannel endorectal coil (ERC) for use in combination with an external surface array (ESA) for high-resolution anatomical and functional studies of the prostate at 7T. MATERIALS AND METHODS A two-loop ERC (ERC-2L) and a microstrip-loop ERC (ERC-ML) were compared at 7T in terms of transmit and receive performance. The best-performing ERC was evaluated alone and in combination with the ESA through 1) simulations on both phantom and an anatomically correct numerical human model to assess B1+ transmit and specific absorption rate (SAR) efficiencies, and 2) phantom experiments to calculate B1+ transmit efficiency and signal-to-noise ratio (SNR). Phantom studies were also performed to look at heating when using the ERC as a transmitter and for comparing the new coil against a single-channel balloon-type ERC (ERC-b). High-resolution magnetic resonance imaging (MRI) acquisitions were performed on a single healthy subject using the two-channel ERC combined with the ESA. RESULTS Compared to the ERC-ML, the ERC-2L demonstrated 20% higher SAR efficiency and higher SNR 3 cm from the coil. The presence of a tuned and detuned ERC-2L did not alter the peak local SAR of the ESA alone; however, the detuned ERC-2L had 45% less peak local SAR around the rectum compared to the tuned ERC-2L. The receive-only version of the ERC-2L improved the SNR 4.7-fold and 1.3-fold compared to the ESA and ERC-b, respectively. In combination with the ESA, the ERC-2L supported in-plane voxel-size of 0.36 × 0.36 mm(2) in T2 -weighted anatomic imaging. CONCLUSION The reusable ERC-2L combined with an ESA offers a high SNR imaging platform for translational studies of the prostate at 7T. J. Magn. Reson. Imaging 2016;43:1279-1287.
Collapse
Affiliation(s)
- M Arcan Ertürk
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Jinfeng Tian
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | | | - Gregor Adriany
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| | - Gregory J Metzger
- Center for Magnetic Resonance Research, University of Minnesota Medical School, Minneapolis, Minnesota, USA
| |
Collapse
|
96
|
van de Bank BL, Orzada S, Smits F, Lagemaat MW, Rodgers CT, Bitz AK, Scheenen TWJ. Optimized (31)P MRS in the human brain at 7 T with a dedicated RF coil setup. NMR IN BIOMEDICINE 2015; 28:1570-8. [PMID: 26492089 PMCID: PMC4744789 DOI: 10.1002/nbm.3422] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2015] [Revised: 09/02/2015] [Accepted: 09/06/2015] [Indexed: 05/03/2023]
Abstract
The design and construction of a dedicated RF coil setup for human brain imaging ((1)H) and spectroscopy ((31)P) at ultra-high magnetic field strength (7 T) is presented. The setup is optimized for signal handling at the resonance frequencies for (1)H (297.2 MHz) and (31)P (120.3 MHz). It consists of an eight-channel (1)H transmit-receive head coil with multi-transmit capabilities, and an insertable, actively detunable (31)P birdcage (transmit-receive and transmit only), which can be combined with a seven-channel receive-only (31)P array. The setup enables anatomical imaging and (31)P studies without removal of the coil or the patient. By separating transmit and receive channels and by optimized addition of array signals with whitened singular value decomposition we can obtain a sevenfold increase in SNR of (31)P signals in the occipital lobe of the human brain compared with the birdcage alone. These signals can be further enhanced by 30 ± 9% using the nuclear Overhauser effect by B1-shimmed low-power irradiation of water protons. Together, these features enable acquisition of (31)P MRSI at high spatial resolutions (3.0 cm(3) voxel) in the occipital lobe of the human brain in clinically acceptable scan times (~15 min).
Collapse
Affiliation(s)
- Bart L van de Bank
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Stephan Orzada
- Erwin L. Hahn Institute, University Hospital Duisburg-Essen, Essen, Germany
| | - Frits Smits
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Miriam W Lagemaat
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
| | - Christopher T Rodgers
- Oxford Centre for Clinical Magnetic Resonance Research (OCMR), University of Oxford, John Radcliffe Hospital, Oxford, UK
| | - Andreas K Bitz
- Erwin L. Hahn Institute, University Hospital Duisburg-Essen, Essen, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Tom W J Scheenen
- Department of Radiology and Nuclear Medicine, Radboud University Medical Center, Nijmegen, The Netherlands
- Erwin L. Hahn Institute, University Hospital Duisburg-Essen, Essen, Germany
| |
Collapse
|
97
|
Ni D, Zhang J, Bu W, Zhang C, Yao Z, Xing H, Wang J, Duan F, Liu Y, Fan W, Feng X, Shi J. PEGylated NaHoF4 nanoparticles as contrast agents for both X-ray computed tomography and ultra-high field magnetic resonance imaging. Biomaterials 2015; 76:218-25. [PMID: 26546914 DOI: 10.1016/j.biomaterials.2015.10.063] [Citation(s) in RCA: 69] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2015] [Revised: 10/16/2015] [Accepted: 10/26/2015] [Indexed: 12/30/2022]
Abstract
It is well-known that multimodal imaging can integrate the advantages of different imaging modalities by overcoming their individual limitations. As ultra-high field magnetic resonance imaging (MRI) will be inevitably used in future MRI/X-ray computed tomography (CT) scanner, it is highly expected to develop high-performance nano-contrast agents for ultra-high field MR and CT dual-modality imaging, which has not been reported yet. Moreover, specific behavior of nano-contrast agents for ultra-high field MRI is a challenging work and still remains unknown. Herein, a novel type of NaHoF4 nanoparticles (NPs) with varied particle sizes were synthesized and explored as high-performance dual-modality contrast agents for ultra-high field MR and CT imaging. The specific X-ray absorption and MR relaxivity enhancements with varied nanoparticle diameters (3 nm, 7 nm, 13 nm and 29 nm) under different magnetic field (1.5/3.0/7.0 T) are investigated. Based on experimental results and theoretical analysis, the Curie and dipolar relaxation mechanisms of NaHoF4 NPs are firstly separated. Our results will greatly promote the future medical translational development of the NaHoF4 nano-contrast agents for ultra-high field MR/CT dual-modality imaging applications.
Collapse
Affiliation(s)
- Dalong Ni
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Jiawen Zhang
- Department of Radiology, Huashan Hospital, Fudan University, Shanghai, 200040, China
| | - Wenbo Bu
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China.
| | - Chen Zhang
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Zhenwei Yao
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China.
| | - Huaiyong Xing
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Jing Wang
- Department of Radiology, Huashan Hospital, Fudan University, Shanghai, 200040, China
| | - Fei Duan
- Department of Radiology, Huashan Hospital, Fudan University, Shanghai, 200040, China
| | - Yanyan Liu
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Wenpei Fan
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China
| | - Xiaoyuan Feng
- Department of Radiology, Huashan Hospital, Fudan University, Shanghai, 200040, China
| | - Jianlin Shi
- State Key Laboratory of High Performance Ceramics and Superfine Microstructures, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050, China.
| |
Collapse
|
98
|
Buonincontri G, Sawiak SJ. MR fingerprinting with simultaneous B1 estimation. Magn Reson Med 2015; 76:1127-35. [PMID: 26509746 PMCID: PMC5061105 DOI: 10.1002/mrm.26009] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2015] [Revised: 09/14/2015] [Accepted: 09/14/2015] [Indexed: 12/12/2022]
Abstract
PURPOSE MR fingerprinting (MRF) can be used for quantitative estimation of physical parameters in MRI. Here, we extend the method to incorporate B1 estimation. METHODS The acquisition is based on steady state free precession MR fingerprinting with a Cartesian trajectory. To increase the sensitivity to the B1 profile, abrupt changes in flip angle were introduced in the sequence. Slice profile and B1 effects were included in the dictionary and the results from two- and three-dimensional (3D) acquisitions were compared. Acceleration was demonstrated using retrospective undersampling in the phase encode directions of 3D data exploiting redundancy between MRF frames at the edges of k-space. RESULTS Without B1 estimation, T2 and B1 were inaccurate by more than 20%. Abrupt changes in flip angle improved B1 maps. T1 and T2 values obtained with the new MRF methods agree with classical spin echo measurements and are independent of the B1 field profile. When using view sharing reconstruction, results remained accurate (error <10%) when sampling under 10% of k-space from the 3D data. CONCLUSION The methods demonstrated here can successfully measure T1, T2, and B1. Errors due to slice profile can be substantially reduced by including its effect in the dictionary or acquiring data in 3D. Magn Reson Med 76:1127-1135, 2016. © 2015 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Collapse
Affiliation(s)
- Guido Buonincontri
- Istituto Nazionale di Fisica Nucleare (INFN), sezione di Pisa, Largo B. Pontecorvo, Pisa (PI), Italy.
| | - Stephen J Sawiak
- Wolfson Brain Imaging Centre, Department of Clinical Neurosciences, University of Cambridge, Addenbrooke's Hospital, Hills Road, Cambridge, United Kingdom
| |
Collapse
|
99
|
Bluemink JJ, Raaijmakers AJE, Koning W, Andreychenko A, Rivera DS, Luijten PR, Klomp DWJ, van den Berg CAT. Dielectric waveguides for ultrahigh field magnetic resonance imaging. Magn Reson Med 2015; 76:1314-24. [DOI: 10.1002/mrm.26007] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2014] [Revised: 09/11/2015] [Accepted: 09/12/2015] [Indexed: 11/09/2022]
Affiliation(s)
- Johanna J. Bluemink
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Alexander J. E. Raaijmakers
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Wouter Koning
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Anna Andreychenko
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Debra S. Rivera
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Peter R. Luijten
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Dennis W. J. Klomp
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| | - Cornelis A. T. van den Berg
- UMC Utrecht Cancer Center / UMC Utrecht Center for Imaging Sciences, Department of Radiotherapy; University Medical Center Utrecht; The Netherlands
| |
Collapse
|
100
|
Weidman EK, Dean KE, Rivera W, Loftus ML, Stokes TW, Min RJ. MRI safety: a report of current practice and advancements in patient preparation and screening. Clin Imaging 2015; 39:935-7. [PMID: 26422769 DOI: 10.1016/j.clinimag.2015.09.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Accepted: 09/01/2015] [Indexed: 11/18/2022]
Abstract
MRI offers detailed diagnostic images without ionizing radiation; however, there are considerable safety concerns associated with high electromagnetic field strength. With increasing use of high and ultra high (7T) magnetic field strength, adequate patient preparation and screening for ferrous material is increasingly important. We review current safety standards for patient screening and preparation and how they are implemented at our institution. In addition, we describe a novel supplemental screening technique wherein the lights are dimmed in response to detected ferrous metal at the threshold of Zone IV.
Collapse
Affiliation(s)
- Elizabeth K Weidman
- Department of Radiology, NewYork-Presbyterian Weill Cornell, 525 E. 68th St, New York, NY 10065
| | - Kathryn E Dean
- Department of Radiology, NewYork-Presbyterian Weill Cornell, 525 E. 68th St, New York, NY 10065
| | - William Rivera
- Weill Cornell Imaging at NewYork-Presbyterian, 520 East 70th Street, New York, NY 10021
| | - Michael L Loftus
- Department of Radiology, NewYork-Presbyterian Weill Cornell, 525 E. 68th St, New York, NY 10065
| | - Thomas W Stokes
- Weill Cornell Imaging at NewYork-Presbyterian, 520 East 70th Street, New York, NY 10021
| | - Robert J Min
- Department of Radiology, NewYork-Presbyterian Weill Cornell, 525 E. 68th St, New York, NY 10065; Weill Cornell Imaging at NewYork-Presbyterian, 520 East 70th Street, New York, NY 10021.
| |
Collapse
|