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Murali S, Ding H, Adedeji F, Qin C, Obungoloch J, Asllani I, Anazodo U, Ntusi NAB, Mammen R, Niendorf T, Adeleke S. Bringing MRI to low- and middle-income countries: Directions, challenges and potential solutions. NMR IN BIOMEDICINE 2024; 37:e4992. [PMID: 37401341 DOI: 10.1002/nbm.4992] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/20/2022] [Revised: 05/27/2023] [Accepted: 05/30/2023] [Indexed: 07/05/2023]
Abstract
The global disparity of magnetic resonance imaging (MRI) is a major challenge, with many low- and middle-income countries (LMICs) experiencing limited access to MRI. The reasons for limited access are technological, economic and social. With the advancement of MRI technology, we explore why these challenges still prevail, highlighting the importance of MRI as the epidemiology of disease changes in LMICs. In this paper, we establish a framework to develop MRI with these challenges in mind and discuss the different aspects of MRI development, including maximising image quality using cost-effective components, integrating local technology and infrastructure and implementing sustainable practices. We also highlight the current solutions-including teleradiology, artificial intelligence and doctor and patient education strategies-and how these might be further improved to achieve greater access to MRI.
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Affiliation(s)
- Sanjana Murali
- School of Medicine, Faculty of Medicine, Imperial College London, London, UK
| | - Hao Ding
- School of Medicine, Faculty of Medicine, Imperial College London, London, UK
| | - Fope Adedeji
- School of Medicine, Faculty of Medicine, University College London, London, UK
| | - Cathy Qin
- Department of Imaging, Imperial College Healthcare NHS Trust, London, UK
| | - Johnes Obungoloch
- Department of Biomedical Engineering, Mbarara University of Science and Technology, Mbarara, Uganda
| | - Iris Asllani
- Department of Biomedical Engineering, Rochester Institute of Technology, Rochester, New York, USA
| | - Udunna Anazodo
- Department of Medical Biophysics, Western University, London, Ontario, Canada
- The Research Institute of London Health Sciences Centre and St. Joseph's Health Care, London, Ontario, Canada
| | - Ntobeko A B Ntusi
- Department of Medicine, University of Cape Town and Groote Schuur Hospital, Cape Town, South Africa
- South African Medical Research Council Extramural Unit on Intersection of Noncommunicable Diseases and Infectious Diseases, Cape Town, South Africa
| | - Regina Mammen
- Department of Cardiology, The Essex Cardiothoracic Centre, Basildon, UK
| | - Thoralf Niendorf
- Berlin Ultrahigh Field Facility (BUFF), Max-Delbrück Centre for Molecular Medicine in the Helmholtz Association, Berlin, Germany
| | - Sola Adeleke
- School of Cancer & Pharmaceutical Sciences, King's College London, London, UK
- High Dimensional Neuro-oncology, University College London Queen Square Institute of Neurology, Faculty of Brain Sciences, University College London, London, UK
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2
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Motovilova E, Winkler SA. Overview of Methods for Noise and Heat Reduction in MRI Gradient Coils. FRONTIERS IN PHYSICS 2022; 10:907619. [PMID: 36506821 PMCID: PMC9733908 DOI: 10.3389/fphy.2022.907619] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Magnetic resonance imaging (MRI) gradient coils produce acoustic noise due to coil conductor vibrations caused by large Lorentz forces. Accurate sound pressure levels and modeling of heating are essential for the assessment of gradient coil safety. This work reviews the state-of-the-art numerical methods used in accurate gradient coil modeling and prediction of sound pressure levels (SPLs) and temperature rise. We review several approaches proposed for noise level reduction of high-performance gradient coils, with a maximum noise reduction of 20 decibels (dB) demonstrated. An efficient gradient cooling technique is also presented.
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Affiliation(s)
- Elizaveta Motovilova
- Department of Radiology, Weill Cornell Medicine, New York, NY, United States
- Department of Radiology, Hospital for Special Surgery, New York, NY, United States
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3
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Versteeg E, Klomp DWJ, Siero JCW. A silent gradient axis for soundless spatial encoding to enable fast and quiet brain imaging. Magn Reson Med 2021; 87:1062-1073. [PMID: 34545956 PMCID: PMC9293127 DOI: 10.1002/mrm.29010] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2021] [Revised: 08/17/2021] [Accepted: 08/30/2021] [Indexed: 12/22/2022]
Abstract
Purpose A novel silent imaging method is proposed that combines a gradient insert oscillating at the inaudible frequency 20 kHz with slew rate‐limited gradient waveforms to form a silent gradient axis that enable quiet and fast imaging. Methods The gradient insert consisted of a plug‐and‐play (45 kg) single axis z‐gradient, which operated as an additional fourth gradient axis. This insert was made resonant using capacitors and combined with an audio amplifier to allow for operation at 20 kHz. The gradient field was characterized using field measurements and the physiological effects of operating a gradient field at 20 kHz were explored using peripheral nerve stimulation experiments, tissue heating simulations and sound measurements. The imaging sequence consisted of a modified gradient‐echo sequence which fills k‐space in readout lanes with a width proportional to the oscillating gradient amplitude. The feasibility of the method was demonstrated in‐vivo using 2D and 3D gradient echo (GRE) sequences which were reconstructed using a conjugate‐gradient SENSE reconstruction. Results Field measurements yielded a maximum gradient amplitude and slew rate of 40.8 mT/m and 5178T/m/s at 20 kHz. Physiological effects such as peripheral nerve stimulation and tissue heating were found not to be limiting at this amplitude and slew rate. For a 3D GRE sequence, a maximum sound level of 85 db(A) was measured during scanning. Imaging experiments using the silent gradient axis produced artifact free images while also featuring a 5.3‐fold shorter scan time than a fully sampled acquisition. Conclusion A silent gradient axis provides a novel pathway to fast and quiet brain imaging.
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Affiliation(s)
- Edwin Versteeg
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Dennis W J Klomp
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Jeroen C W Siero
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.,Spinoza Center for Neuroimaging, Amsterdam, Netherlands
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4
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Versteeg E, van der Velden TA, van Leeuwen CC, Borgo M, Huijing ER, Hendriks AD, Hendrikse J, Klomp DWJ, Siero JCW. A plug-and-play, lightweight, single-axis gradient insert design for increasing spatiotemporal resolution in echo planar imaging-based brain imaging. NMR IN BIOMEDICINE 2021; 34:e4499. [PMID: 33619838 PMCID: PMC8244051 DOI: 10.1002/nbm.4499] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2019] [Revised: 02/09/2021] [Accepted: 02/11/2021] [Indexed: 05/25/2023]
Abstract
The goal of this study was to introduce and evaluate the performance of a lightweight, high-performance, single-axis (z-axis) gradient insert design primarily intended for high-resolution functional magnetic resonance imaging, and aimed at providing both ease of use and a boost in spatiotemporal resolution. The optimal winding positions of the coil were obtained using a genetic algorithm with a cost function that balanced gradient performance (minimum 0.30 mT/m/A) and field linearity (≥16 cm linear region). These parameters were verified using field distribution measurements by B0 -mapping. The correction of geometrical distortions was performed using theoretical field distribution of the coil. Simulations and measurements were performed to investigate the echo planar imaging echo-spacing reduction due to the improved gradient performance. The resulting coil featured a 16-cm linear region, a weight of 45 kg, an installation time of 15 min, and a maximum gradient strength and slew rate of 200 mT/m and 1300 T/m/s, respectively, when paired with a commercially available gradient amplifier (940 V/630 A). The field distribution measurements matched the theoretically expected field. By utilizing the theoretical field distribution, geometrical distortions were corrected to within 6% of the whole-body gradient reference image in the target region. Compared with a whole-body gradient set, a maximum reduction in echo-spacing of a factor of 2.3 was found, translating to a 344 μs echo-spacing, for a field of view of 192 mm, a receiver bandwidth of 920 kHz and a gradient amplitude of 112 mT/m. We present a lightweight, single-axis gradient insert design that can provide high gradient performance and an increase in spatiotemporal resolution with correctable geometrical distortions while also offering a short installation time of less than 15 min and minimal system modifications.
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Affiliation(s)
- Edwin Versteeg
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | | | | | | | - Erik R. Huijing
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Arjan D. Hendriks
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Jeroen Hendrikse
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Dennis W. J. Klomp
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
| | - Jeroen C. W. Siero
- Department of RadiologyUniversity Medical Center UtrechtUtrechtthe Netherlands
- Spinoza Center for NeuroimagingAmsterdamthe Netherlands
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Davids M, Guerin B, Klein V, Wald LL. Optimization of MRI Gradient Coils With Explicit Peripheral Nerve Stimulation Constraints. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:129-142. [PMID: 32915730 PMCID: PMC7772273 DOI: 10.1109/tmi.2020.3023329] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Peripheral Nerve Stimulation (PNS) limits the acquisition rate of Magnetic Resonance Imaging data for fast sequences employing powerful gradient systems. The PNS characteristics are currently assessed after the coil design phase in experimental stimulation studies using constructed coil prototypes. This makes it difficult to find design modifications that can reduce PNS. Here, we demonstrate a direct approach for incorporation of PNS effects into the coil optimization process. Knowledge about the interactions between the applied magnetic fields and peripheral nerves allows the optimizer to identify coil solutions that minimize PNS while satisfying the traditional engineering constraints. We compare the simulated thresholds of PNS-optimized body and head gradients to conventional designs, and find an up to 2-fold reduction in PNS propensity with moderate penalties in coil inductance and field linearity, potentially doubling the image encoding performance that can be safely used in humans. The same framework may be useful in designing and operating magneto- and electro-stimulation devices.
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6
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Handler WB, Bindseil G, Chaddock R, Dalrymple B, Gati JS, Gilbert KM, Harris CT, Klassen ML, Peterson J, Van Sas F, Chronik BA. Design and construction of a gradient coil for high resolution marmoset imaging. Biomed Phys Eng Express 2020; 6:045022. [PMID: 33444282 DOI: 10.1088/2057-1976/ab8d97] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
A gradient coil with integrated second and third order shims has been designed and constructed for use inside an actively shielded 310 mm horizontal bore 9.4 T small animal MRI. An extension of the boundary element method, to minimise the power deposited in conducting surfaces, was used to design the gradients, and a boundary element method with a constraint on mutual inductance was used to design the shims. The gradient coil allows for improved imaging performance and was optimized for an imaging region appropriate for marmoset imaging studies. Efficiencies of 1.5 mT m-1 A-1 were achieved in a 15 cm wide bore while maintaining gradient uniformity ≤5% over the 8 cm region of interest. Two new cooling methods were implemented which allowed the gradient coil to operate at 100 A RMS, 25 % of max current with a temperature rise below 30 C.
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Affiliation(s)
- William B Handler
- xMR lab, Physics and Astronomy Department, Western University, London, Ontario, Canada
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7
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Yang Z, Zhao B, Pei Y, Yang B, Lu H. A "flared-end" gradient coil with outer-wall direct cooling for human brain imaging: A feasibility study. Magn Reson Imaging 2019; 62:191-198. [PMID: 31306733 DOI: 10.1016/j.mri.2019.07.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2019] [Revised: 07/11/2019] [Accepted: 07/11/2019] [Indexed: 11/16/2022]
Abstract
Optimal gradient performance is arguably a pre-requisite to realize the full potential of ultrahigh field magnetic resonance imaging (MRI). The values of using tailored gradient coils for brain imaging have been well acknowledged. Unfortunately, conventional head-only gradient coils have two major technical limitations, i.e. limited shoulder clearance and limited cooling capacity. A design, coined "flared-end" gradient coil, combined with a cooling method, named "outer-wall direct cooling", is proposed to address these problems. The "flared-end" design permits brain access to the center of gradient coil. The "flared end" structure is 3D-printed. It has electrical winding patterns (grooves) on one side and evenly spaced cooling channels on the opposite side. Electrical conductor (copper wire) is fixed into the grooves; coolant is in direct contact with the outer surface of the electrical conductor above each cooling channel, eliminating interfacial thermal resistance between coolant and copper wires. Heat transfer area is thus determined by the size and the number of cooling channels. This approach allows high electric current density for high gradient field strength while maintaining high cooling efficiency. Additionally, the symmetric coil geometry guarantees intrinsic torque balance. As a proof of concept, we have made a gradient coil prototype without active shielding. This coil has an inner diameter of 0.3 m, and is capable of generating 0.337, 0.225 and 0.485 mT/m/A along X, Y and Z, respectively. Active shielding was designed theoretically, but not pursued in the construction of this coil prototype. The new coil geometry and cooling method offer a novel avenue for new gradient coils tailored for human brain imaging at ultrahigh field.
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Affiliation(s)
- Zhi Yang
- Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA
| | - Beihan Zhao
- Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA
| | - Yong Pei
- Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA
| | - Bao Yang
- Department of Mechanical Engineering, University of Maryland, College Park, MD 20742, USA.
| | - Hanbing Lu
- Neuroimaging Research Branch, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD 21224, USA.
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8
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Tang F, Hao J, Freschi F, Niu C, Repetto M, Liu F, Crozier S. A cone-shaped gradient coil design for high-resolution MRI head imaging. Phys Med Biol 2019; 64:085003. [PMID: 30780134 DOI: 10.1088/1361-6560/ab084a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Insertable head gradient coils offer significant advantages such as high gradient strength and fast gradient switching speed owing to shorter distances to the target region of interest than whole-body cylindrical coils. To produce superior gradient performance, the local head coil is typically designed with an asymmetric configuration to accommodate both the shoulders and head of a patient, leading to tough dimensional constraints and practical limits to the coil implementation. In this paper, we propose a new cone-shaped model to improve the performance of the asymmetric head coils and to mitigate patient claustrophobia. The primary coils are designed with a larger diameter at the patient end for access and a smaller diameter at the service end to bring wires closer to the human head, while the secondary coils are arranged on a cylindrical former to improve coil efficiency. Two cases are studied in this paper. Case I: inner bore size at the patient end (diameter 42 cm) is fixed as the design reference. In this case, inner diameters at any other position vary with the conical tilting angles. Compared with a set of conical gradient coils designed with tilting angles ranging from 0 to 14°, it is found that the optimal coil performance is achieved at the tilting angle of 14°. The key performance parameters have been improved by 100%-200% for the transverse coils, and about 50% for the longitudinal coils compared with the cylindrical counterpart with the reference bore size (that is, the same diameter of 42 cm). The conical coils also produce less heat in the gradient structure and lower acoustic noise in the field of view. Case II: inner bore size at the iso-centre (diameter 34 cm) is set as the design reference. It is also found that, compared with 34 cm diameter cylindrical coils, the conical transverse coil performance has been improved at an angle of 14°. The key coil performance increases by 20%-50% for transverse coil but decreases by 20%-40% for the longitudinal coil. However, compared with the tight cylindrical structure (e.g. 34 cm diameter), the tilting angle will provide patient-friendly space for imaging and handling, which can be critical for fMRI and other brain studies.
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Affiliation(s)
- Fangfang Tang
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
| | - Jiahao Hao
- College of Optoelectronic Engineering, Chongqing University, Chongqing 400030, People's Republic of China
| | - Fabio Freschi
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.,Department of Energy, Politecnico di Torino Corso Duca Degli Abruzzi, 24 10129 Torino, Italy
| | - Chaoqun Niu
- Division of Superconducting Magnet Science and Technology, Institute of Electrical Engineering, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.,University of Chinese Academy of Sciences, Beijing 100083, People's Republic of China
| | - Maurizio Repetto
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.,Department of Energy, Politecnico di Torino Corso Duca Degli Abruzzi, 24 10129 Torino, Italy
| | - Feng Liu
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia.,Author to whom any correspondence should be addressed
| | - Stuart Crozier
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD 4072, Australia
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9
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Winkler SA, Schmitt F, Landes H, de Bever J, Wade T, Alejski A, Rutt BK. Gradient and shim technologies for ultra high field MRI. Neuroimage 2018; 168:59-70. [PMID: 27915120 PMCID: PMC5591082 DOI: 10.1016/j.neuroimage.2016.11.033] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 10/06/2016] [Accepted: 11/12/2016] [Indexed: 02/08/2023] Open
Abstract
Ultra High Field (UHF) MRI requires improved gradient and shim performance to fully realize the promised gains (SNR as well as spatial, spectral, diffusion resolution) that higher main magnetic fields offer. Both the more challenging UHF environment by itself, as well as the higher currents used in high performance coils, require a deeper understanding combined with sophisticated engineering modeling and construction, to optimize gradient and shim hardware for safe operation and for highest image quality. This review summarizes the basics of gradient and shim technologies, and outlines a number of UHF-related challenges and solutions. In particular, Lorentz forces, vibroacoustics, eddy currents, and peripheral nerve stimulation are discussed. Several promising UHF-relevant gradient concepts are described, including insertable gradient coils aimed at higher performance neuroimaging.
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Affiliation(s)
| | | | | | | | - Trevor Wade
- Imaging Research Laboratories, Robarts Research Institute, Canada
| | - Andrew Alejski
- Imaging Research Laboratories, Robarts Research Institute, Canada
| | - Brian K Rutt
- Department of Radiology, Stanford University, USA
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10
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Predicting Magnetostimulation Thresholds in the Peripheral Nervous System using Realistic Body Models. Sci Rep 2017; 7:5316. [PMID: 28706244 PMCID: PMC5509681 DOI: 10.1038/s41598-017-05493-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2017] [Accepted: 05/30/2017] [Indexed: 12/01/2022] Open
Abstract
Rapid switching of applied magnetic fields in the kilohertz frequency range in the human body induces electric fields powerful enough to cause Peripheral Nerve Stimulation (PNS). PNS has become one of the main constraints on the use of high gradient fields for fast imaging with the latest MRI gradient technology. In recent MRI gradients, the applied fields are powerful enough that PNS limits their application in fast imaging sequences like echo-planar imaging. Application of Magnetic Particle Imaging (MPI) to humans is similarly PNS constrained. Despite its role as a major constraint, PNS considerations are only indirectly incorporated in the coil design process, mainly through using the size of the linear region as a proxy for PNS thresholds or by conducting human experiments after constructing coil prototypes. We present for the first time, a framework to simulate PNS thresholds for realistic coil geometries to directly address PNS in the design process. Our PNS model consists of an accurate body model for electromagnetic field simulations, an atlas of peripheral nerves, and a neurodynamic model to predict the nerve responses to imposed electric fields. With this model, we were able to reproduce measured PNS thresholds of two leg/arm solenoid coils with good agreement.
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11
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Tang F, Liu F, Freschi F, Li Y, Repetto M, Giaccone L, Wang Y, Crozier S. An improved asymmetric gradient coil design for high-resolution MRI head imaging. Phys Med Biol 2016; 61:8875-8889. [PMID: 27910827 DOI: 10.1088/1361-6560/61/24/8875] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
For head magnetic resonance imaging, local gradient coils are often used to achieve high solution images. To accommodate the human head and shoulder, the head gradient coils are usually designed in an asymmetric configuration, allowing the region-of-uniformity (ROU) close to the coil's patient end. However, the asymmetric configuration leads to technical difficulties in maintaining a high gradient performance for the insertable head coil with very limited space. In this work, we present a practical design configuration of an asymmetric insertable gradient head coil offering an improved performance. In the proposed design, at the patient end, the primary and secondary coils are connected using an additional radial surface, thus allowing the coil conductors distributed on the flange to ensure an improvement in the coil performance. At the service end, the primary and shielding coils are not connected, to permit access to shim trays, cooling system piping, cabling, and so on. The new designs are compared with conventional coil configurations and the simulation results show that, with a similar field quality in the ROU, the proposed coil pattern has improved construction characteristics (open service end, well-distributed wire pattern) and offers a better coil performance (lower inductance, higher efficiency, etc) than conventional head coil configurations.
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Affiliation(s)
- Fangfang Tang
- School of Information Technology and Electrical Engineering, the University of Queensland, Brisbane, QLD 4072, Australia
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12
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Winkler SA, Alejski A, Wade T, McKenzie CA, Rutt BK. On the accurate analysis of vibroacoustics in head insert gradient coils. Magn Reson Med 2016; 78:1635-1645. [PMID: 27859549 DOI: 10.1002/mrm.26543] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 10/13/2016] [Accepted: 10/16/2016] [Indexed: 11/07/2022]
Abstract
PURPOSE To accurately analyze vibroacoustics in MR head gradient coils. THEORY AND METHODS A detailed theoretical model for gradient coil vibroacoustics, including the first description and modeling of Lorentz damping, is introduced and implemented in a multiphysics software package. Numerical finite-element method simulations were used to establish a highly accurate vibroacoustic model in head gradient coils in detail, including the newly introduced Lorentz damping effect. Vibroacoustic coupling was examined through an additional modal analysis. Thorough experimental studies were used to validate simulations. RESULTS Average experimental sound pressure levels (SPLs) and accelerations over the 0-3000 Hz frequency range were 97.6 dB, 98.7 dB, and 95.4 dB, as well as 20.6 g, 8.7 g, and 15.6 g for the X-, Y-, and Z-gradients, respectively. A reasonable agreement between simulations and measurements was achieved. Vibroacoustic coupling showed a coupled resonance at 2300 Hz for the Z-gradient that is responsible for a sharp peak and the highest SPL value in the acoustic spectrum. CONCLUSION We have developed and used more realistic multiphysics simulation methods to gain novel insights into the underlying concepts for vibroacoustics in head gradient coils, which will permit improved analyses of existing gradient coils and novel SPL reduction strategies for future gradient coil designs. Magn Reson Med 78:1635-1645, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Simone A Winkler
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Andrew Alejski
- Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada
| | - Trevor Wade
- Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada.,The Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Charles A McKenzie
- Robarts Research Institute, The University of Western Ontario, London, Ontario, Canada.,The Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Brian K Rutt
- Department of Radiology, Stanford University, Stanford, California, USA
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13
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Littin S, Gallichan D, Welz AM, Jia F, Dewdney A, Weber H, Schultz G, Hennig J, Zaitsev M. Monoplanar gradient system for imaging with nonlinear gradients. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2015; 28:447-57. [PMID: 25684133 DOI: 10.1007/s10334-015-0481-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2014] [Revised: 01/05/2015] [Accepted: 01/22/2015] [Indexed: 11/27/2022]
Abstract
OBJECT In this paper we present a monoplanar gradient system capable of imaging a volume comparable with that covered by linear gradient systems. Such a system has been designed and implemented. MATERIALS AND METHODS Building such a system was made possible by relaxing the constraint of global linearity and replacing it with a requirement for local orthogonality. A framework was derived for optimization of local orthogonality within the physical boundaries and geometric constraints. Spatial encoding of magnetic fields was optimized for their local orthogonality over a large field of view. RESULTS A coil design consisting of straight wire segments was optimized, implemented, and integrated into a 3T human scanner to show the feasibility of this approach. Initial MR images are shown and further applications of the derived optimization method and the nonlinear planar gradient system are discussed. CONCLUSION Encoding fields generated by the prototype encoding system were shown to be locally orthogonal and able to encode a cylindrical volume sufficient for some abdomen imaging applications for humans.
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Affiliation(s)
- Sebastian Littin
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany.
| | | | - Anna Masako Welz
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
| | - Feng Jia
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
| | | | - Hans Weber
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
| | - Gerrit Schultz
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
| | - Jürgen Hennig
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
| | - Maxim Zaitsev
- Department of Diagnostic Radiology, Medical Physics, University Medical Center Freiburg, Breisacher Str. 60a, 79106, Freiburg, Germany
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