1
|
Hadi YH, Hawsawi HB, Abu Aqil AI. Driving healthcare forward: The potential of mobile MRI and CT units in streamlining radiological services in Saudi Arabia - A narrative review. J Med Imaging Radiat Sci 2024; 55:101444. [PMID: 38986296 DOI: 10.1016/j.jmir.2024.101444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2024] [Revised: 05/20/2024] [Accepted: 05/27/2024] [Indexed: 07/12/2024]
Abstract
BACKGROUND AND PURPOSE This narrative review focuses on the role of mobile MRI and CT units in addressing the challenges of healthcare accessibility and patient wait times in Saudi Arabia. It underscores the growing demand for diagnostic imaging amid infrastructural and geographical barriers, emphasizing mobile units as innovative solutions for enhancing radiological services across diverse Saudi landscapes. The purpose of this study is to assess how these mobile technologies can mitigate service delays, improve patient outcomes, and support healthcare delivery in remote or underserved areas, reflecting on global trends towards more dynamic, patient-centered healthcare models. METHODS This review utilizes an expanded database search and refined keywords to ensure comprehensive literature coverage. The study focused on peer-review articles and grey literatures that directly examined the impact of these mobile units on healthcare accessibility, wait times, and service delivery. A thematic analysis identified significant contributions to accessibility improvements, emergency responses, and rural healthcare, highlighting areas for further research and policy development. DISCUSSION Mobile units have advanced technical specifications with high-field magnets and multi-slice CT scanners on par with fixed facilities. They prioritize patient comfort and safety with examination areas, control rooms, and waiting areas. Telemedicine capabilities allow real-time image transmission to specialists. Strategic deployment can address workforce shortages by distributing services equitably. Mobile units represent cost-effective solutions to expand healthcare access without fixed infrastructure. CONCLUSION Integration of mobile MRI and CT units in Saudi Arabia can transform access to diagnostic imaging by decentralizing services and directly reaching patients, including rural areas. Evidence shows mobile units reduce diagnostic delays and optimize resource use. Despite challenges, strategic investments and collaborations can overcome obstacles to make radiological services more equitable, flexible and patient-focused in Saudi Arabia.
Collapse
Affiliation(s)
- Yasser H Hadi
- Department of Medical Imaging and Intervention, King Abdullah Medical City (KAMC), Muzdalifah Rd, Al Mashair, Makkah 24246, Saudi Arabia; Discipline of Medical Imaging and Radiation Therapy, School of Medicine, University College Cork, Brookfield, College Rd, University College, Cork, T12 AK54, Ireland.
| | - Hassan B Hawsawi
- Department of Medical Physics, King Abdullah Medical City (KAMC), Muzdalifah Rd, Al Mashair, Makkah 24246, Saudi Arabia
| | | |
Collapse
|
2
|
Samardzija A, Selvaganesan K, Zhang HZ, Sun H, Sun C, Ha Y, Galiana G, Constable RT. Low-Field, Low-Cost, Point-of-Care Magnetic Resonance Imaging. Annu Rev Biomed Eng 2024; 26:67-91. [PMID: 38211326 DOI: 10.1146/annurev-bioeng-110122-022903] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2024]
Abstract
Low-field magnetic resonance imaging (MRI) has recently experienced a renaissance that is largely attributable to the numerous technological advancements made in MRI, including optimized pulse sequences, parallel receive and compressed sensing, improved calibrations and reconstruction algorithms, and the adoption of machine learning for image postprocessing. This new attention on low-field MRI originates from a lack of accessibility to traditional MRI and the need for affordable imaging. Low-field MRI provides a viable option due to its lack of reliance on radio-frequency shielding rooms, expensive liquid helium, and cryogen quench pipes. Moreover, its relatively small size and weight allow for easy and affordable installation in most settings. Rather than replacing conventional MRI, low-field MRI will provide new opportunities for imaging both in developing and developed countries. This article discusses the history of low-field MRI, low-field MRI hardware and software, current devices on the market, advantages and disadvantages, and low-field MRI's global potential.
Collapse
Affiliation(s)
- Anja Samardzija
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
| | - Kartiga Selvaganesan
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
| | - Horace Z Zhang
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
| | - Heng Sun
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
| | - Chenhao Sun
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, Connecticut, USA
| | - Yonghyun Ha
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, Connecticut, USA
| | - Gigi Galiana
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, Connecticut, USA
| | - R Todd Constable
- Department of Biomedical Engineering, Yale University, New Haven, Connecticut, USA;
- Department of Radiology and Biomedical Imaging, Yale School of Medicine, New Haven, Connecticut, USA
| |
Collapse
|
3
|
de Vos B, Remis R, Webb A. Segmented RF shield design to minimize eddy currents for low-field Halbach MRI systems. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2024; 362:107669. [PMID: 38598991 DOI: 10.1016/j.jmr.2024.107669] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Revised: 03/29/2024] [Accepted: 04/03/2024] [Indexed: 04/12/2024]
Abstract
MRI systems have a thin conducting layer placed between the gradient and RF coils, this acts as a shield at the RF-frequency, minimizing noise coupled into the experiment, and decreasing the coupling between the RF and gradient coils. Ideally, this layer should be transparent to the gradient fields to reduce eddy currents. In this work the design of such a shield, specifically for low-field point-of-care Halbach based MRI devices, is discussed. A segmented double layer shield is designed and constructed based on eddy current simulations. Subsequently, the performance of the improved shield is compared to a reference shield by measuring the eddy current decay times as well as using noise measurements. A maximum reduction factor of 2.9 in the eddy current decay time is observed. The segmented shield couples in an equivalent amount of noise when compared to the unsegmented reference shield. Turbo spin echo images of a phantom and the brain of a healthy volunteer show improvements in terms of blurring using the segmented shield.
Collapse
Affiliation(s)
- Bart de Vos
- C.J. Gorter MRI center, Radiology, Leiden University Center, Leiden, The Netherlands; Terahertz Sensing, Microelectronics, Delft University of Technology, Delft, The Netherlands.
| | - Rob Remis
- Terahertz Sensing, Microelectronics, Delft University of Technology, Delft, The Netherlands
| | - Andrew Webb
- C.J. Gorter MRI center, Radiology, Leiden University Center, Leiden, The Netherlands; Terahertz Sensing, Microelectronics, Delft University of Technology, Delft, The Netherlands
| |
Collapse
|
4
|
de Vos B, Remis RF, Webb AG. Characterization of concomitant gradient fields and their effects on image distortions using a low-field point-of-care Halbach-based MRI system. Magn Reson Med 2024; 91:828-841. [PMID: 37749850 DOI: 10.1002/mrm.29879] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Revised: 09/07/2023] [Accepted: 09/08/2023] [Indexed: 09/27/2023]
Abstract
PURPOSE Concomitant gradient fields have been extensively studied at clinical field strengths. However, their effects have not yet been modeled for low-field point-of-care (POC) systems. The purpose of this work is to characterize the effects associated with concomitant fields for POC Halbach-array-based systems. METHODS The concomitant fields associated with a cylindrical gradient coils designed for a transverseB 0 $$ {B}_0 $$ and a signal model including the tilting effect of the effective magnetic field are derived. The formalism is used to simulate and predict concomitant field related distortions. A 46-mT Halbach-array-based system with a maximum gradient strength of 15 mT/m is used to verify the model using two-dimensional spin-echo sequences. RESULTS The simulations and experimental results are in good agreement with the derived equations. The fundamental characteristics of the concomitant field equations are different to conventional MRI systems: Image distortions occur primarily in the transverse directions and a cross-term only exists when applying transverse gradient pulses simultaneously. CONCLUSION The level of image warping in the frequency encoding direction is insignificant for the POC systems discussed here. However, when trying to achieve short echo-times by using strong phase encoding and readout-dephasing gradients, the combination can result in image warping and blurring which should be accounted for in image interpretation.
Collapse
Affiliation(s)
- Bart de Vos
- Radiology, C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, The Netherlands
| | - Rob F Remis
- Micro-electronics, Signal Processing Systems, Delft University of Technology, Delft, The Netherlands
| | - Andrew G Webb
- Radiology, C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, The Netherlands
- Micro-electronics, Terahertz Sensing, Delft University of Technology, Delft, The Netherlands
| |
Collapse
|
5
|
Sherman SE, Zammit AS, Heo WS, Rosen MS, Cima MJ. Single-sided magnetic resonance-based sensor for point-of-care evaluation of muscle. Nat Commun 2024; 15:440. [PMID: 38199994 PMCID: PMC10782019 DOI: 10.1038/s41467-023-44561-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Accepted: 12/19/2023] [Indexed: 01/12/2024] Open
Abstract
Magnetic resonance imaging is a widespread clinical tool for the detection of soft tissue morphology and pathology. However, the clinical deployment of magnetic resonance imaging scanners is ultimately limited by size, cost, and space constraints. Here, we discuss the design and performance of a low-field single-sided magnetic resonance sensor intended for point-of-care evaluation of skeletal muscle in vivo. The 11 kg sensor has a penetration depth of >8 mm, which allows for an accurate analysis of muscle tissue and can avoid signal from more proximal layers, including subcutaneous adipose tissue. Low operational power and shielding requirements are achieved through the design of a permanent magnet array and surface transceiver coil. The sensor can acquire high signal-to-noise measurements in minutes, making it practical as a point-of-care tool for many quantitative diagnostic measurements, including T2 relaxometry. In this work, we present the in vitro and human in vivo performance of the device for muscle tissue evaluation.
Collapse
Affiliation(s)
- Sydney E Sherman
- Harvard-MIT Program in Health Science and Technology, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Alexa S Zammit
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Won-Seok Heo
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
| | - Matthew S Rosen
- Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Boston, MA, 02129, USA
- Harvard Medical School, Boston, MA, 02115, USA
- Department of Physics, Harvard University, Cambridge, MA, 02138, USA
| | - Michael J Cima
- Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
| |
Collapse
|
6
|
Jalloul M, Miranda-Schaeubinger M, Noor AM, Stein JM, Amiruddin R, Derbew HM, Mango VL, Akinola A, Hart K, Weygand J, Pollack E, Mohammed S, Scheel JR, Shell J, Dako F, Mhatre P, Kulinski L, Otero HJ, Mollura DJ. MRI scarcity in low- and middle-income countries. NMR IN BIOMEDICINE 2023; 36:e5022. [PMID: 37574441 DOI: 10.1002/nbm.5022] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2023] [Revised: 07/19/2023] [Accepted: 07/21/2023] [Indexed: 08/15/2023]
Abstract
Since the introduction of MRI as a sustainable diagnostic modality, global accessibility to its services has revealed a wide discrepancy between populations-leaving most of the population in LMICs without access to this important imaging modality. Several factors lead to the scarcity of MRI in LMICs; for example, inadequate infrastructure and the absence of a dedicated workforce are key factors in the scarcity observed. RAD-AID has contributed to the advancement of radiology globally by collaborating with our partners to make radiology more accessible for medically underserved communities. However, progress is slow and further investment is needed to ensure improved global access to MRI.
Collapse
Affiliation(s)
- Mohammad Jalloul
- Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | | | - Abass M Noor
- Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
- RAD-AID International, Chevy Chase, Maryland, USA
- Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Joel M Stein
- Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Raisa Amiruddin
- Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | - Hermon Miliard Derbew
- Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
- College of Health Science, Addis Ababa University, Addis Ababa, Ethiopia
| | - Victoria L Mango
- RAD-AID International, Chevy Chase, Maryland, USA
- Memorial Sloan Kettering Cancer Center, New York, New York, USA
| | | | - Kelly Hart
- Tufts Medical Center, Boston, Massachusetts, USA
| | | | - Erica Pollack
- RAD-AID International, Chevy Chase, Maryland, USA
- University of Colorado Anschutz Medical Center, Aurora, Colorado, USA
| | - Sharon Mohammed
- RAD-AID International, Chevy Chase, Maryland, USA
- Bellevue Hospital Center NYCHHC, New York, New York, USA
| | - John R Scheel
- RAD-AID International, Chevy Chase, Maryland, USA
- Vanderbilt University Medical Center, Nashville, Tennessee, USA
| | - Jessica Shell
- RAD-AID International, Chevy Chase, Maryland, USA
- Siemens Medical Solutions USA, Inc., Cary, North Carolina, USA
| | - Farouk Dako
- RAD-AID International, Chevy Chase, Maryland, USA
- Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | - Pradnya Mhatre
- RAD-AID International, Chevy Chase, Maryland, USA
- Emory University School of Medicine, Atlanta, Georgia, USA
| | | | - Hansel J Otero
- Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA
| | | |
Collapse
|
7
|
Cima M, Sherman S, Zammit A, Heo WS, Rosen M. Single-sided magnetic resonance-based sensor for point-of-care evaluation of muscle. RESEARCH SQUARE 2023:rs.3.rs-3335248. [PMID: 37790511 PMCID: PMC10543496 DOI: 10.21203/rs.3.rs-3335248/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
Magnetic resonance (MR) imaging is a powerful clinical tool for the detection of soft tissue morphology and pathology, which often provides actionable diagnostic information to clinicians. Its clinical use is largely limited due to size, cost, time, and space constraints. Here, we discuss the design and performance of a low-field single-sided MR sensor intended for point-of-care (POC) evaluation of skeletal muscle in vivo. The 11kg sensor has a penetration depth of > 8 mm, which allows for an accurate analysis of muscle tissue and can avoid signal from more proximal layers, including subcutaneous adipose tissue. Low operational power and minimal shielding requirements are achieved through the design of a permanent magnet array and surface transceiver coil. We present the in vitro and human in vivo performance of the device for muscle tissue evaluation. The sensor can acquire high signal-to-noise (SNR > 150) measurements in minutes, making it practical as a POC tool for many quantitative diagnostic measurements, including T2 relaxometry.
Collapse
Affiliation(s)
| | | | | | | | - Matthew Rosen
- Massachusetts General Hospital and Harvard Medical School
| |
Collapse
|
8
|
Miyasaka T, Kajiwara M, Kawasaki A, Okamoto Y, Terada Y. Development of a Car-mounted Mobile MR Imaging System for Diagnosis of Sports-related Wrist Injury. Magn Reson Med Sci 2023; 22:379-387. [PMID: 35473757 PMCID: PMC10449548 DOI: 10.2463/mrms.tn.2021-0158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Accepted: 03/12/2022] [Indexed: 11/09/2022] Open
Abstract
Portable MRI scanners, in which a permanent magnet with a low magnetic field is mounted on a small car, have enabled the performance of MRI examinations in various remote environments. Here, we have modified the portable MRI system to enable the early diagnosis of wrist sports injuries among tennis players. A RF probe specifically designed for the human wrist was developed, and a power supply scheme using a small generator was introduced. The portable MRI system was located at a tennis school and imaging of the wrists of junior tennis players was performed. To demonstrate clinical feasibility, image quality was assessed by a radiologist and clinical evaluations were performed. In most cases, the image quality was sufficient for diagnosis, and triangular fibrocartilage complex damage could be detected. The results indicated that the modified portable MRI system could be applied for an early diagnosis of wrist injuries.
Collapse
Affiliation(s)
- Tomoki Miyasaka
- Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Michiru Kajiwara
- Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Akito Kawasaki
- Graduate School of Human Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Yoshikazu Okamoto
- Institute of Clinical Medicine, Department of Diagnostic and Interventional Radiology, University of Tsukuba, Tsukuba, Ibaraki, Japan
| | - Yasuhiko Terada
- Institute of Applied Physics, University of Tsukuba, Tsukuba, Ibaraki, Japan
| |
Collapse
|
9
|
de Vos B, Remis RF, Webb AG. An integrated target field framework for point-of-care halbach array low-field MRI system design. MAGMA (NEW YORK, N.Y.) 2023:10.1007/s10334-023-01093-z. [PMID: 37208554 PMCID: PMC10386967 DOI: 10.1007/s10334-023-01093-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/14/2022] [Revised: 01/18/2023] [Accepted: 04/16/2023] [Indexed: 05/21/2023]
Abstract
OBJECTIVE Low-cost low-field point-of-care MRI systems are used in many different applications. System design has correspondingly different requirements in terms of imaging field-of-view, spatial resolution and magnetic field strength. In this work an iterative framework has been created to design a cylindrical Halbach-based magnet along with integrated gradient and RF coils that most efficiently fulfil a set of user-specified imaging requirements. METHODS For efficient integration, target field methods are used for each of the main hardware components. These have not been used previously in magnet design, and a new mathematical model was derived accordingly. These methods result in a framework which can design an entire low-field MRI system within minutes using standard computing hardware. RESULTS Two distinct point-of-care systems are designed using the described framework, one for neuroimaging and the other for extremity imaging. Input parameters are taken from literature and the resulting systems are discussed in detail. DISCUSSION The framework allows the designer to optimize the different hardware components with respect to the desired imaging parameters taking into account the interdependencies between these components and thus give insight into the influence of the design choices.
Collapse
Affiliation(s)
- Bart de Vos
- C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, Netherlands.
| | - Rob F Remis
- Signal Processing Systems, Delft University of Technology, Delft, Netherlands
| | - Andrew G Webb
- C.J. Gorter MRI Center, Leiden University Medical Center, Leiden, Netherlands
- Signal Processing Systems, Delft University of Technology, Delft, Netherlands
| |
Collapse
|
10
|
Webb A, O'Reilly T. Tackling SNR at low-field: a review of hardware approaches for point-of-care systems. MAGMA (NEW YORK, N.Y.) 2023:10.1007/s10334-023-01100-3. [PMID: 37202656 PMCID: PMC10386948 DOI: 10.1007/s10334-023-01100-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2022] [Revised: 05/03/2023] [Accepted: 05/09/2023] [Indexed: 05/20/2023]
Abstract
OBJECTIVE To review the major hardware components of low-field point-of-care MRI systems which affect the overall sensitivity. METHODS Designs for the following components are reviewed and analyzed: magnet, RF coils, transmit/receive switches, preamplifiers, data acquisition system, and methods for grounding and mitigating electromagnetic interference. RESULTS High homogeneity magnets can be produced in a variety of different designs including C- and H-shaped as well as Halbach arrays. Using Litz wire for RF coil designs enables unloaded Q values of ~ 400 to be reached, with body loss representing about 35% of the total system resistance. There are a number of different schemes to tackle issues arising from the low coil bandwidth with respect to the imaging bandwidth. Finally, the effects of good RF shielding, proper electrical grounding, and effective electromagnetic interference reduction can lead to substantial increases in image signal-to-noise ratio. DISCUSSION There are many different magnet and RF coil designs in the literature, and to enable meaningful comparisons and optimizations to be performed it would be very helpful to determine a standardized set of sensitivity measures, irrespective of design.
Collapse
Affiliation(s)
- Andrew Webb
- Department of Radiology, C.J. Gorter MRI Center, Leiden University Medical Center, 2333 ZA, Leiden, The Netherlands.
| | - Thomas O'Reilly
- Department of Radiology, C.J. Gorter MRI Center, Leiden University Medical Center, 2333 ZA, Leiden, The Netherlands
| |
Collapse
|
11
|
Haskell MW, Nielsen JF, Noll DC. Off-resonance artifact correction for MRI: A review. NMR IN BIOMEDICINE 2023; 36:e4867. [PMID: 36326709 PMCID: PMC10284460 DOI: 10.1002/nbm.4867] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Revised: 09/25/2022] [Accepted: 11/01/2022] [Indexed: 06/06/2023]
Abstract
In magnetic resonance imaging (MRI), inhomogeneity in the main magnetic field used for imaging, referred to as off-resonance, can lead to image artifacts ranging from mild to severe depending on the application. Off-resonance artifacts, such as signal loss, geometric distortions, and blurring, can compromise the clinical and scientific utility of MR images. In this review, we describe sources of off-resonance in MRI, how off-resonance affects images, and strategies to prevent and correct for off-resonance. Given recent advances and the great potential of low-field and/or portable MRI, we also highlight the advantages and challenges of imaging at low field with respect to off-resonance.
Collapse
Affiliation(s)
- Melissa W Haskell
- Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan, USA
- Hyperfine Research, Guilford, Connecticut, USA
| | | | - Douglas C Noll
- Biomedical Engineering, University of Michigan, Ann Arbor, Michigan, USA
| |
Collapse
|
12
|
Negnevitsky V, Vives-Gilabert Y, Algarín JM, Craven-Brightman L, Pellicer-Guridi R, O'Reilly T, Stockmann JP, Webb A, Alonso J, Menküc B. MaRCoS, an open-source electronic control system for low-field MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 350:107424. [PMID: 37001194 DOI: 10.1016/j.jmr.2023.107424] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2022] [Revised: 02/20/2023] [Accepted: 03/13/2023] [Indexed: 05/10/2023]
Abstract
Every magnetic resonance imaging (MRI) device requires an electronic control system that handles pulse sequences and signal detection and processing. Here we provide details on the architecture and performance of MaRCoS, a MAgnetic Resonance COntrol System developed by an open international community of low-field MRI researchers. MaRCoS is inexpensive and can handle cycle-accurate sequences without hard length limitations, rapid bursts of events, and arbitrary waveforms. It has also been readily adapted to meet the requirements of the various academic and private institutions participating in its development. We describe the MaRCoS hardware, firmware and software that enable all of the above, including a Python-based graphical user interface for pulse sequence implementation, data processing and image reconstruction.
Collapse
Affiliation(s)
| | - Yolanda Vives-Gilabert
- Intelligent Data Analysis Laboratory, Department of Electronic Engineering, Universitat de València, Valencia, Spain
| | - José M Algarín
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M), Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV), Valencia, Spain
| | - Lincoln Craven-Brightman
- Massachusetts General Hospital, A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| | - Rubén Pellicer-Guridi
- Asociación de Investigación MPC, Manuel de Lardizábal 5, Donostia-San Sebastián 20018, Spain
| | - Thomas O'Reilly
- Department of Radiology, Leiden University Medical Center, Albinusdreef 2, Leiden 2333, Netherlands
| | - Jason P Stockmann
- Massachusetts General Hospital, A. A. Martinos Center for Biomedical Imaging, Charlestown, MA, USA
| | - Andrew Webb
- Department of Radiology, Leiden University Medical Center, Albinusdreef 2, Leiden 2333, Netherlands
| | - Joseba Alonso
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M), Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV), Valencia, Spain
| | - Benjamin Menküc
- University of Applied Sciences and Arts Dortmund, Sonnenstr. 96, Dortmund 44139, Germany.
| |
Collapse
|
13
|
Wei S, Wei Z, Wang Z, Wang H, He Q, He H, Li L, Yang W. Optimization design of a permanent magnet used for a low field (0.2 T) movable MRI system. MAGMA (NEW YORK, N.Y.) 2023:10.1007/s10334-023-01090-2. [PMID: 37081246 DOI: 10.1007/s10334-023-01090-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Revised: 04/06/2023] [Accepted: 04/11/2023] [Indexed: 04/22/2023]
Abstract
OBJECTIVE To design a lightweight permanent magnet for a lowfield movable head imaging MRI system. MATERIALS AND METHODS To reduce the weight of the magnet, the pole pieces, anti-eddy current plates, and shimming rings were removed, and the distance between the two vertical yokes was shortened as much as possible. To compensate for the magnetic field deformation caused by the shortened distance between two vertical iron yokes, two side magnetic poles were added to the vertical yokes. The magnetic field distributions in magnetic poles, the iron yoke, and the spherical imaging region were simulated. Phantom and in vivo head imaging were conducted with a lowfield movable MRI prototype scanner equipped with the proposed permanent magnet. RESULTS A permanent magnet with a center field of 0.19815 T, a homogeneity of 46 ppm over the 20 cm spherical imaging region, and a weight of 654 kg have been achieved. Acceptable images of a phantom and a human brain have been acquired with the prototype MRI scanner. DISCUSSION The proposed permanent magnet design significantly reduces the magnet's weight compared with the conventional magnet structure and shows promise in promoting the development of lowfield compact MRI systems.
Collapse
Affiliation(s)
- Shufeng Wei
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
| | - Zhao Wei
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
| | - Zheng Wang
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
| | - Huixian Wang
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
| | - Qingyuan He
- Peking University Third Hospital, Beijing, 100191, China
| | - Hongyan He
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Lei Li
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China
- University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Wenhui Yang
- Department of Electromagnetic Detection and Imaging Research, Institute of Electrical Engineering, Chinese Academy of Sciences, Zhongguancun Beiertiao NO.6, Beijing, 100190, China.
- University of Chinese Academy of Sciences, Beijing, 100049, China.
| |
Collapse
|
14
|
Guallart‐Naval T, O'Reilly T, Algarín JM, Pellicer‐Guridi R, Vives‐Gilabert Y, Craven‐Brightman L, Negnevitsky V, Menküc B, Galve F, Stockmann JP, Webb A, Alonso J. Benchmarking the performance of a low-cost magnetic resonance control system at multiple sites in the open MaRCoS community. NMR IN BIOMEDICINE 2023; 36:e4825. [PMID: 36097704 PMCID: PMC10078257 DOI: 10.1002/nbm.4825] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 08/15/2022] [Accepted: 08/26/2022] [Indexed: 05/15/2023]
Abstract
PURPOSE To describe the current properties and capabilities of an open-source hardware and software package that is being developed by many sites internationally with the aim of providing an inexpensive yet flexible platform for low-cost MRI. METHODS This article describes three different setups from 50 to 360 mT in different settings, all of which used the MaRCoS console for acquiring data, and different types of software interface (custom-built GUI or Pulseq overlay) to acquire it. RESULTS Images are presented both from phantoms and in vivo from healthy volunteers to demonstrate the image quality that can be obtained from the MaRCoS hardware/software interfaced to different low-field magnets. CONCLUSIONS The results presented here show that a number of different sequences commonly used in the clinic can be programmed into an open-source system relatively quickly and easily, and can produce good quality images even at this early stage of development. Both the hardware and software will continue to develop, and it is an aim of this article to encourage other groups to join this international consortium.
Collapse
Affiliation(s)
- Teresa Guallart‐Naval
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
- Tesoro Imaging S.L.ValenciaSpain
| | - Thomas O'Reilly
- Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| | - José M. Algarín
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
| | | | - Yolanda Vives‐Gilabert
- Intelligent Data Analysis Laboratory, Department of Electronic EngineeringUniversitat de ValènciaValenciaSpain
| | | | | | - Benjamin Menküc
- University of Applied Sciences and Arts DortmundDortmundGermany
| | - Fernando Galve
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
| | - Jason P. Stockmann
- Massachusetts General Hospital, A. A. Martinos Center for Biomedical ImagingCharlestownMAUSA
| | - Andrew Webb
- Department of RadiologyLeiden University Medical CenterLeidenThe Netherlands
| | - Joseba Alonso
- MRILab, Institute for Molecular Imaging and Instrumentation (i3M)Spanish National Research Council (CSIC) and Universitat Politècnica de València (UPV)ValenciaSpain
| |
Collapse
|
15
|
Arnold TC, Freeman CW, Litt B, Stein JM. Low-field MRI: Clinical promise and challenges. J Magn Reson Imaging 2023; 57:25-44. [PMID: 36120962 PMCID: PMC9771987 DOI: 10.1002/jmri.28408] [Citation(s) in RCA: 62] [Impact Index Per Article: 62.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2022] [Revised: 08/11/2022] [Accepted: 08/12/2022] [Indexed: 02/03/2023] Open
Abstract
Modern MRI scanners have trended toward higher field strengths to maximize signal and resolution while minimizing scan time. However, high-field devices remain expensive to install and operate, making them scarce outside of high-income countries and major population centers. Low-field strength scanners have drawn renewed academic, industry, and philanthropic interest due to advantages that could dramatically increase imaging access, including lower cost and portability. Nevertheless, low-field MRI still faces inherent limitations in image quality that come with decreased signal. In this article, we review advantages and disadvantages of low-field MRI scanners, describe hardware and software innovations that accentuate advantages and mitigate disadvantages, and consider clinical applications for a new generation of low-field devices. In our review, we explore how these devices are being or could be used for high acuity brain imaging, outpatient neuroimaging, MRI-guided procedures, pediatric imaging, and musculoskeletal imaging. Challenges for their successful clinical translation include selecting and validating appropriate use cases, integrating with standards of care in high resource settings, expanding options with actionable information in low resource settings, and facilitating health care providers and clinical practice in new ways. By embracing both the promise and challenges of low-field MRI, clinicians and researchers have an opportunity to transform medical care for patients around the world. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY: Stage 6.
Collapse
Affiliation(s)
- Thomas Campbell Arnold
- Department of Bioengineering, School of Engineering & Applied ScienceUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
- Center for Neuroengineering and TherapeuticsUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Colbey W. Freeman
- Department of Radiology, Perelman School of MedicineUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Brian Litt
- Center for Neuroengineering and TherapeuticsUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
- Department of Neurology, Perelman School of MedicineUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| | - Joel M. Stein
- Center for Neuroengineering and TherapeuticsUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
- Department of Radiology, Perelman School of MedicineUniversity of PennsylvaniaPhiladelphiaPennsylvaniaUSA
| |
Collapse
|
16
|
Sakai M, Mutsuzaki H, Shimizu Y, Okamoto Y, Nakajima T. Characteristic MRI findings of the shoulder, elbow, and wrist joints in elite wheelchair basketball players. BMC Sports Sci Med Rehabil 2022; 14:141. [PMID: 35870996 PMCID: PMC9308260 DOI: 10.1186/s13102-022-00528-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 07/13/2022] [Indexed: 11/26/2022] Open
Abstract
Background The health of wheelchair users’ upper limbs is directly related to their quality of life. Moreover, para-sport athletes are subjected to a dual load on their upper extremities from competition and daily life, making it even more critical to maintain upper extremity health. This study aimed to investigate the characteristics of joint disorders in elite wheelchair basketball players using magnetic resonance imaging (MRI). Methods We scanned MRI images of the bilateral shoulders, elbows, and wrist joints of ten elite wheelchair basketball players and ten general wheelchair users. The elite wheelchair players were athletes who underwent at our institution medical checkup of the candidates for the national team for the international women's tournament and who agreed to this research purpose. The general wheelchair players were recruited from wheelchair users in their 20s and 30s who had no daily exercise habits and who agreed to the study objectives. Two radiologists interpreted the MRI images and diagnosed the diseases of each joint. We compared the number of lesions between the two groups. We used Fisher's exact test to determine whether the lesions diagnosed by MRI were specific to wheelchair basketball players. The significance threshold was set at P < 0.05. Results Elite wheelchair basketball players had significantly more right-sided, left-sided and bilateral latero-posterior lesions, which are cysts found on the lateral-posterior corner of the capitulum of the humerus than did general wheelchair users (P < 0.05). Severe damage to the right triangular fibrocartilage complex was also observed more frequently (P < 0.05) in wheelchair basketball players. Conclusions We believe that the patients’ tendency to fall forward in the wheelchair hitting both hands on the ground, thereby injuring the triangular fibrocartilage complex and locking the lateral elbow, may be the cause of the characteristic findings on MRI. High-speed wheelchair operation was also considered a cause of severe triangular fibrocartilage complex injuries. This study's insights can be useful for future solutions to extend players' careers.
Collapse
|
17
|
Liang TO, Koh YH, Qiu T, Li E, Yu W, Huang SY. High-performance permanent magnet array design by a fast genetic algorithm (GA)-based optimization for low-field portable MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 345:107309. [PMID: 36335876 DOI: 10.1016/j.jmr.2022.107309] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 08/21/2022] [Accepted: 10/08/2022] [Indexed: 06/16/2023]
Abstract
Lightweight and compact permanent magnet arrays (PMAs) are suitable for portable dedicated magnetic resonance imaging (MRI). It is worth exploring different PMA design possibilities and optimization methods with an adequate balance between weight, size, and performance, in addition to Halbach arrays and C-shaped/H-shaped magnets which are widely used. In this paper, the design and optimization of a sparse high-performance inward-outward ring-pair PMA consisting of magnet cuboids is presented for portable imaging of the brain. The design is lightweight (151kg) and compact (inner bore diameter: 270mm, outer diameter: 616mm, length: 480mm, 5-Gauss range: 1840×1840×2340mm3). The optimization framework is based on the genetic algorithm with a consideration of both field properties and simulated image quality. The resulting PMA design has an average field strength of 101.5 mT and a field pattern with a built-in linear readout gradient. Subtracting the best fit to the linear gradient target resulted in a residual deviation from the target field of 0.76mT and an average linear regression coefficient of 0.85 to the linear gradient. The required radiofrequency bandwidth is 6.9% within a field of view (FoV) with a diameter of 200mm and a length of 125mm. It has a magnetic field generation efficiency of 0.67mT/kg, which is high among the sparse PMAs that were designed for an FoV with a diameter of 200mm. The field can be used to supply gradients in one direction working with gradient coils in the other two directions, or can be rotated to encode signals for imaging with axial slice selection. The encoding capability of the designed PMA was examined through the simulated reconstructed images. The force experienced by each magnet in the design was calculated, and the feasibility of a physical implementation was confirmed. The design can offer an increased field strength, and thus, an increased signal-to-noise ratio. It has a longitudinal field direction that allows the application of technologies developed for solenoidal magnets. This proposed design can be a promising alternative to supplying the main and gradient fields in combination for dedicated portable MRI. Lastly, the design is resulted from a fast genetic algorithm-based optimization in which fast magnetic field calculation was applied and high design flexibility was feasible. Within optimization iterations, image quality metrics were used for the encoding field of a magnet configuration to guide the design of the magnet array.
Collapse
Affiliation(s)
- Ting-Ou Liang
- Singapore University of Technology and Design 8 Somapah Road, 487372, Singapore
| | - Yan Hao Koh
- Singapore University of Technology and Design 8 Somapah Road, 487372, Singapore
| | - Tie Qiu
- Singapore University of Technology and Design 8 Somapah Road, 487372, Singapore
| | - Erping Li
- Zhejiang University Hangzhou, Zhejiang Province, China
| | - Wenwei Yu
- Center for Frontier Medical Engineering, Chiba University Inage Ku, Yayoi Cho, 1-33, Chiba 263-8522, Japan
| | - Shao Ying Huang
- Singapore University of Technology and Design 8 Somapah Road, 487372, Singapore; Department of Surgery, Yong Loo Lin School of Medicine, National University of Singapore IE Kent Ridge Road, 119228, Singapore.
| |
Collapse
|
18
|
Liu M, Li Q, Chen G, Su N, Zhou M, Liu X, Sun K. The value of mobile magnetic resonance imaging in early warning for stroke: A prospective case-control study. Front Neurosci 2022; 16:975217. [PMID: 36033625 PMCID: PMC9411978 DOI: 10.3389/fnins.2022.975217] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Accepted: 07/27/2022] [Indexed: 11/23/2022] Open
Abstract
Aims To evaluate the predictive value of mobile magnetic resonance imaging (MRI) in screening stroke. Methods This was a prospective case-control study performed on healthy residents over 40 years old in remote rural areas of northern China between May 2019 and May 2020. Multivariate logistic regression and receiver operator characteristic curve (ROC) analysis were used to evaluate the screening model. Results A total of 1,224 patients (500 [40.8%] men) enrolled, including 56 patients who suffered from stroke (aged 64.05 ± 7.27). The individuals who developed stroke were significantly older (P < 0.001), had a significantly higher occurrence of heart disease (P = 0.015), diabetes (P = 0.005), dyslipidemia (P = 0.009), and significantly increased waist circumference (P = 0.02), systolic blood pressure (SBP) (P = 0.003), glycosylated hemoglobin (HbA1c) level (P = 0.007), triglyceride (TG) level (P = 0.025), low density lipoprotein cholesterol (LDL-c) level (P = 0.04), and homocysteine (HCY) level (P < 0.001). Multivariate logistic regression analysis showed that age (OR = 1.055, 95% CI: 1.017–1.094, P = 0.004), HCY (OR = 1.029, 95% CI: 1.012–1.047, P = 0.001) and mobile MRI (OR = 4.539, 95% CI: 1.726–11.939, P = 0.002) were independently associated with stroke. The area under the curve (AUC) of the combined model including national screening criteria, mobile MRI results, and stroke risk factors was 0.786 (95% CI: 0.721–0.851), with a sensitivity of 69.6% and specificity of 80.4%. Conclusion Mobile MRI can be used as a simple and easy means to screen stroke.
Collapse
Affiliation(s)
- Miaomiao Liu
- The Third People’s Hospital of Longgang District, Shenzhen, China
- Graduate School of Baotou Medical College, Inner Mongolia University of Science and Technology, Baotou, China
| | - Qingyang Li
- Department of Radiology, The First Clinical Medical College of Inner Mongolia Medical University, Huhhot, China
| | - Guoqiang Chen
- Department of Radiology, Baotou Central Hospital, Baotou, China
| | - Ning Su
- Department of Radiology, Baotou Central Hospital, Baotou, China
| | - Maorong Zhou
- Department of Radiology, Baotou Central Hospital, Baotou, China
| | - Xiaolin Liu
- Department of Radiology, Baotou Central Hospital, Baotou, China
| | - Kai Sun
- The Third People’s Hospital of Longgang District, Shenzhen, China
- *Correspondence: Kai Sun,
| |
Collapse
|
19
|
Guallart-Naval T, Algarín JM, Pellicer-Guridi R, Galve F, Vives-Gilabert Y, Bosch R, Pallás E, González JM, Rigla JP, Martínez P, Lloris FJ, Borreguero J, Marcos-Perucho Á, Negnevitsky V, Martí-Bonmatí L, Ríos A, Benlloch JM, Alonso J. Portable magnetic resonance imaging of patients indoors, outdoors and at home. Sci Rep 2022; 12:13147. [PMID: 35907975 PMCID: PMC9338984 DOI: 10.1038/s41598-022-17472-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Accepted: 07/26/2022] [Indexed: 12/25/2022] Open
Abstract
Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI technology companies have demonstrated the first decisive steps towards portability within medical facilities and vehicles. However, these scanners' weight and dimensions are incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, small footprint, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer's knee in: (i) an MRI physics laboratory; (ii) an office room; (iii) outside a campus building, connected to a nearby power outlet; (iv) in open air, powered from a small fuel-based generator; and (v) at the volunteer's home. All images have been acquired within clinically viable times, and signal-to-noise ratios and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic.
Collapse
Affiliation(s)
| | - José M Algarín
- Institute for Molecular Imaging and Instrumentation, Spanish National Research Council, 46022, Valencia, Spain
- Institute for Molecular Imaging and Instrumentation, Universitat Politècnica de València, 46022, Valencia, Spain
| | - Rubén Pellicer-Guridi
- PhysioMRI Tech S.L., 46022, Valencia, Spain
- Asociación de investigación MPC, 20018, San Sebastián, Spain
| | - Fernando Galve
- Institute for Molecular Imaging and Instrumentation, Spanish National Research Council, 46022, Valencia, Spain
- Institute for Molecular Imaging and Instrumentation, Universitat Politècnica de València, 46022, Valencia, Spain
| | - Yolanda Vives-Gilabert
- PhysioMRI Tech S.L., 46022, Valencia, Spain
- Intelligent Data Analysis Laboratory, Department of Electronic Engineering, Universitat de València, 46100, Burjassot, Spain
| | | | - Eduardo Pallás
- Institute for Molecular Imaging and Instrumentation, Spanish National Research Council, 46022, Valencia, Spain
- Institute for Molecular Imaging and Instrumentation, Universitat Politècnica de València, 46022, Valencia, Spain
| | | | | | | | | | | | | | | | - Luis Martí-Bonmatí
- Medical Imaging Department, Hospital Universitari i Politècnic La Fe, 46026, Valencia, Spain
| | | | - José M Benlloch
- Institute for Molecular Imaging and Instrumentation, Spanish National Research Council, 46022, Valencia, Spain
- Institute for Molecular Imaging and Instrumentation, Universitat Politècnica de València, 46022, Valencia, Spain
| | - Joseba Alonso
- Institute for Molecular Imaging and Instrumentation, Spanish National Research Council, 46022, Valencia, Spain.
- Institute for Molecular Imaging and Instrumentation, Universitat Politècnica de València, 46022, Valencia, Spain.
| |
Collapse
|
20
|
Su J, Pellicer-Guridi R, Edwards T, Fuentes M, Rosen MS, Vegh V, Reutens D. A CNN Based Software Gradiometer for Electromagnetic Background Noise Reduction in Low Field MRI Applications. IEEE TRANSACTIONS ON MEDICAL IMAGING 2022; 41:1007-1016. [PMID: 35089856 DOI: 10.1109/tmi.2022.3147450] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The shielding of electromagnetic noise is critical in obtaining magnetic resonance imaging measurements in the ultra-low magnetic field regime where the intrinsic signal-to-noise ratio is very small. The traditional approach of using an enclosure for electromagnetic shielding is expensive and hinders system portability. We describe here the use of a CNN-based software gradiometer to suppress the effect of electromagnetic ambient background noise sources that inductively couple into the signal detection coils. The system involves three ambient noise monitoring coils placed at a distance from the magnetic resonance signal detector. The three coils were used to synthesize the ambient noise captured by the signal detector; a convolutional neural network approach was used. Mathematical foundations are provided to justify the noise suppression framework. The results show that as much as 20-fold noise suppression can be achieved using an optimized convolutional neural network and simultaneous ambient noise measurements. The proposed approach has the potential to replace the requirement for magnetically shielded enclosures and make ultra-low field magnetic resonance imaging truly portable.
Collapse
|
21
|
Deoni SCL, Medeiros P, Deoni AT, Burton P, Beauchemin J, D'Sa V, Boskamp E, By S, McNulty C, Mileski W, Welch BE, Huentelman M. Development of a mobile low-field MRI scanner. Sci Rep 2022; 12:5690. [PMID: 35383255 PMCID: PMC8982311 DOI: 10.1038/s41598-022-09760-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Accepted: 03/15/2022] [Indexed: 12/23/2022] Open
Abstract
Magnetic resonance imaging (MRI) allows important visualization of the brain and central nervous system anatomy and organization. However, unlike electroencephalography (EEG) or functional near infrared spectroscopy, which can be brought to a patient or study participant, MRI remains a hospital or center-based modality. Low magnetic field strength MRI systems, however, offer the potential to extend beyond these traditional hospital and imaging center boundaries. Here we describe the development of a modified cargo van that incorporates a removable low-field permanent magnet MRI system and demonstrate its proof-of-concept. Using phantom scans and in vivo T2-weighted neuroimaging data, we show no significant differences with respect to geometric distortion, signal-to-noise ratio, or tissue segmentation outcomes in data acquired in the mobile system compared to a similar static system in a laboratory setting. These encouraging results show, for the first time, MRI that can be performed at a participant’s home, community center, school, etc. Breaking traditional barriers of access, this mobile approach may enable imaging of patients and participants who have mobility challenges, live long distances from imaging centers, or are otherwise unable to travel to an imaging center or hospital.
Collapse
Affiliation(s)
- Sean C L Deoni
- Advanced Baby Imaging Lab, Rhode Island Hospital, Warren Alpert Medical School at Brown University, Providence, RI, USA. .,Department of Diagnostic Radiology, Warren Alpert Medical School at Brown University, Providence, RI, USA. .,Department of Pediatrics, Warren Alpert Medical School at Brown University, Providence, RI, USA.
| | | | - Alexandra T Deoni
- Advanced Baby Imaging Lab, Rhode Island Hospital, Warren Alpert Medical School at Brown University, Providence, RI, USA
| | - Phoebe Burton
- Advanced Baby Imaging Lab, Rhode Island Hospital, Warren Alpert Medical School at Brown University, Providence, RI, USA
| | - Jennifer Beauchemin
- Advanced Baby Imaging Lab, Rhode Island Hospital, Warren Alpert Medical School at Brown University, Providence, RI, USA
| | - Viren D'Sa
- Advanced Baby Imaging Lab, Rhode Island Hospital, Warren Alpert Medical School at Brown University, Providence, RI, USA.,Department of Diagnostic Radiology, Warren Alpert Medical School at Brown University, Providence, RI, USA
| | | | | | | | | | - Brian E Welch
- Hyperfine, Guilford, CT, USA.,Philips North America, Cambridge, MA, USA
| | - Matthew Huentelman
- Neurogenomics Division, Translational Genomics Research Institute, Phoenix, AZ, USA
| |
Collapse
|
22
|
O'Reilly T, Webb AG. In vivo T 1 and T 2 relaxation time maps of brain tissue, skeletal muscle, and lipid measured in healthy volunteers at 50 mT. Magn Reson Med 2021; 87:884-895. [PMID: 34520068 PMCID: PMC9292835 DOI: 10.1002/mrm.29009] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Revised: 08/12/2021] [Accepted: 08/27/2021] [Indexed: 11/10/2022]
Abstract
PURPOSE Low-field (B0 < 0.1 T) MRI has generated much interest as a means of increased accessibility via reduced cost and improved portability compared to conventional clinical systems (B0 ≥ 1.5 Tesla). Here we measure MR relaxation times at 50 mT and compare results with commonly used models based on both in vivo and ex vivo measurements. METHODS Using 3D turbo spin echo readouts, T1 and T2 maps of the human brain and lower leg were acquired on a custom-built 50 mT MRI scanner using inversion-recovery and multi-echo-based sequences, respectively. Image segmentation was performed based on a histogram analysis of the relaxation times. RESULTS The average T1 times of gray matter, white matter, and cerebrospinal fluid (CSF) were 327 ± 10 ms, 275 ± 5 ms, and 3695 ± 287 ms, respectively. Corresponding values of T2 were 102 ± 6 ms, 102 ± 6 ms, and 1584 ± 124 ms. T1 times in the calf muscle were measured to be 171 ± 11 ms and were 130 ± 5 ms in subcutaneous and bone marrow lipid. Corresponding T2 times were 39 ± 2 ms in muscle and 90 ± 13 ms in lipid. CONCLUSIONS For tissues except for CSF, the measured T1 times are much shorter than reported at higher fields and generally lie within the range of different models in the literature. As expected, T2 times are similar to those seen at typical clinical field strengths. Analysis of the relaxation maps indicates that segmentation of white and gray matter based purely on T1 or T2 will be quite challenging at low field given the relatively small difference in relaxation times.
Collapse
Affiliation(s)
- Thomas O'Reilly
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - Andrew G Webb
- Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| |
Collapse
|
23
|
Characterization of displacement forces and image artifacts in the presence of passive medical implants in low-field (<100 mT) permanent magnet-based MRI systems, and comparisons with clinical MRI systems. Phys Med 2021; 84:116-124. [PMID: 33894581 DOI: 10.1016/j.ejmp.2021.04.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2021] [Revised: 03/27/2021] [Accepted: 04/06/2021] [Indexed: 12/19/2022] Open
Abstract
PURPOSE To investigate the displacement forces and image artifacts associated with passive medical implants for recently-developed low-field (<100 mT) MRI systems, and to compare these with values from higher field strengths used for clinical diagnosis. METHODS Setups were constructed to measure displacement forces in a permanent magnet-based Halbach array used for in vivo MRI at 50 mT, and results compared with measurements at 7 T. Image artifacts were assessed using turbo (fast) spin echo imaging sequences for four different passive medical implants: a septal occluder, iliac stent, pedicle screw and (ferromagnetic) endoscopic clip. Comparisons were made with artifacts produced at 1.5, 3 and 7 T. Finally, specific absorption rate (SAR) simulations were performed to determine under what operating conditions the limits might be approached at low-field. RESULTS Displacement forces at 50 mT on all but the ferromagnetic implant were between 1 and 10 mN. Image artifacts at 50 mT were much less than at clinical field strengths for all passive devices, and with the exception of the ferromagnetic clip. SAR simulations show that very long echo train (>128) turbo spin echo sequences can be run with short inter-pulse times (5-10 ms) within SAR limits. CONCLUSIONS This work presents the first evaluation of the effects of passive implants at field strengths less than 100 mT in terms of displacement forces, image artifacts and SAR. The results support previous claims that such systems can be used safely and usefully in challenging enviroments such as the intensive care unit.
Collapse
|
24
|
Abstract
Purpose: Photoacoustics (optoacoustics) is a hybrid technology utilizing light excitation of acoustic responses in targets of interest. It has found numerous applications in biomedicine, including eye research, because of its ability to report both morphological and functional data about the interrogated tissue. This presentation will give an overview of current applications. Methods: Wavelength-dependent absorption of light in a tissue chromophore causes local heating, leading to a thermoelastic expansion-contraction cycle. If nanosecond pulses of light are used to excite this process, the resulting pressure wave is an ultrasound signal propagating through the tissue and detectable at the tissue surface. This is highly advantageous because of the known properties of ultrasound propagation in tissue and the ability to use standard, medical ultrasound equipment for detection. The time of arrival and amplitude of ultrasound signals provide information about the location and nature of the absorber. Results: Due to the wavelength dependence of the photoacoustic response, functional and physiological applications are possible. For example, retinal oximetry can be determined from the different optical absorption properties of oxy- and deoxyhemoglobin. Multispectral imaging of the posterior segment can identify pigments such as melanin or lipofuscin or the nature of foreign bodies. The technique can be combined with other imaging modalities such as ultrasound and optical coherence tomography to produce high-resolution images of retinal structures along with functional information. Conclusion: Photoacoustic technology is a powerful noninvasive tool for ocular research and to study ocular morphology, fundamental physiological parameters, cellular responses, and molecular expression.
Collapse
Affiliation(s)
- Randolph D Glickman
- Department of Ophthalmology, University of Texas Health Science Center at San Antonio, San Antonio, Texas, USA
| |
Collapse
|
25
|
He Y, He W, Tan L, Chen F, Meng F, Feng H, Xu Z. Use of 2.1 MHz MRI scanner for brain imaging and its preliminary results in stroke. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 319:106829. [PMID: 32987217 DOI: 10.1016/j.jmr.2020.106829] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 08/19/2020] [Accepted: 09/07/2020] [Indexed: 05/05/2023]
Abstract
Cerebral stroke greatly contributes to death and disability rates in China and the whole world. Effective non-invasive imaging device for bedside monitoring of stroke is critically needed in clinically. This study developed a lightweight (350 kg) and low-footprint magnetic resonance imaging (MRI) system for brain imaging. Static magnetic field was built using an H-typed permanent magnet, which has 50.9 mT magnetic field strength (corresponding to 2.167 MHz proton Larmor frequency). Biplanar gradient coils were designed using the target field method based on dipole equivalent. Radio-frequency coils were optimized by particle swarm optimization. The 2 MHz MRI system was deployed in the Department of Neurology of hospital to test its performance in stroke imaging detection. Gradient recall echo and fast spin echo sequences were utilized to acquire T1- and T2-weighted MR images, respectively. Brain images of a healthy volunteer, a patient with hemorrhagic stroke, a patient of ischemic stroke, and a patient with ischemic stroke and images from 17-day long-term monitoring of hemorrhagic stroke were obtained with a 1.5 mm * 2.0 mm spatial resolution in plane, and a 10 mm thickness.
Collapse
Affiliation(s)
- Yucheng He
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
| | - Wei He
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
| | - Liang Tan
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China; Department of Neurosurgery, Southwest Hospital, The Third Military Medical University (Army Medical University), Chongqing 400038, China
| | - Fangge Chen
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
| | - Fanqin Meng
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China
| | - Hua Feng
- Department of Neurosurgery, Southwest Hospital, The Third Military Medical University (Army Medical University), Chongqing 400038, China
| | - Zheng Xu
- State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University, Chongqing 400044, China.
| |
Collapse
|
26
|
Wald LL, McDaniel PC, Witzel T, Stockmann JP, Cooley CZ. Low-cost and portable MRI. J Magn Reson Imaging 2020; 52:686-696. [PMID: 31605435 PMCID: PMC10644353 DOI: 10.1002/jmri.26942] [Citation(s) in RCA: 99] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 09/04/2019] [Indexed: 11/16/2023] Open
Abstract
Research in MRI technology has traditionally expanded diagnostic benefit by developing acquisition techniques and instrumentation to enable MRI scanners to "see more." This typically focuses on improving MRI's sensitivity and spatiotemporal resolution, or expanding its range of biological contrasts and targets. In complement to the clear benefits achieved in this direction, extending the reach of MRI by reducing its cost, siting, and operational burdens also directly benefits healthcare by increasing the number of patients with access to MRI examinations and tilting its cost-benefit equation to allow more frequent and varied use. The introduction of low-cost, and/or truly portable scanners, could also enable new point-of-care and monitoring applications not feasible for today's scanners in centralized settings. While cost and accessibility have always been considered, we have seen tremendous advances in the speed and spatial-temporal capabilities of general-purpose MRI scanners and quantum leaps in patient comfort (such as magnet length and bore diameter), but only modest success in the reduction of cost and siting constraints. The introduction of specialty scanners (eg, extremity, brain-only, or breast-only scanners) have not been commercially successful enough to tilt the balance away from the prevailing model: a general-purpose scanner in a centralized healthcare location. Portable MRI scanners equivalent to their counterparts in ultrasound or even computed tomography have not emerged and MR monitoring devices exist only in research laboratories. Nonetheless, recent advances in hardware and computational technology as well as burgeoning markets for MRI in the developing world has created a resurgence of interest in the topic of low-cost and accessible MRI. This review examines the technical forces and trade-offs that might facilitate a large step forward in the push to "jail-break" MRI from its centralized location in healthcare and allow it to reach larger patient populations and achieve new uses. Level of Evidence: 5 Technical Efficacy Stage: 6 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;52:686-696.
Collapse
Affiliation(s)
- Lawrence L. Wald
- Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard Medical School, Boston, Massachusetts, USA
- Division of Health Sciences and Technology, Harvard – Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Patrick C. McDaniel
- Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Thomas Witzel
- Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard Medical School, Boston, Massachusetts, USA
| | - Jason P. Stockmann
- Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard Medical School, Boston, Massachusetts, USA
| | - Clarissa Zimmerman Cooley
- Athinoula A Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Harvard Medical School, Boston, Massachusetts, USA
| |
Collapse
|
27
|
Bhat SS, Fernandes TT, Poojar P, Silva Ferreira M, Rao PC, Hanumantharaju MC, Ogbole G, Nunes RG, Geethanath S. Low‐Field MRI of Stroke: Challenges and Opportunities. J Magn Reson Imaging 2020; 54:372-390. [DOI: 10.1002/jmri.27324] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 07/24/2020] [Accepted: 07/27/2020] [Indexed: 12/12/2022] Open
Affiliation(s)
- Seema S. Bhat
- Medical Imaging Research Centre Dayananda Sagar College of Engineering Bangalore India
| | - Tiago T. Fernandes
- Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal
| | - Pavan Poojar
- Medical Imaging Research Centre Dayananda Sagar College of Engineering Bangalore India
- Columbia University Magnetic Resonance Research Center New York New York USA
| | - Marta Silva Ferreira
- Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal
| | - Padma Chennagiri Rao
- Medical Imaging Research Centre Dayananda Sagar College of Engineering Bangalore India
| | | | - Godwin Ogbole
- Department of Radiology, College of Medicine University of Ibadan Ibadan Nigeria
| | - Rita G. Nunes
- Institute for Systems and Robotics and Department of Bioengineering, Instituto Superior Técnico Universidade de Lisboa Lisbon Portugal
| | - Sairam Geethanath
- Medical Imaging Research Centre Dayananda Sagar College of Engineering Bangalore India
- Columbia University Magnetic Resonance Research Center New York New York USA
| |
Collapse
|
28
|
Greer M, Chen C, Mandal S. An easily reproducible, hand-held, single-sided, MRI sensor. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 308:106591. [PMID: 31546179 DOI: 10.1016/j.jmr.2019.106591] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2019] [Revised: 08/29/2019] [Accepted: 09/03/2019] [Indexed: 06/10/2023]
Abstract
Single-sided MRI sensors allow the imaging of samples that are larger than the magnet. Thus, they enable truly portable imagers with potential applications in medicine, quality assurance (QA), agriculture, material science, and other fields. However, despite recent advancements, single-sided MRI systems are relatively uncommon. This is partially due to the limited number of commercial products. Also, current implementations often require large and/or complex magnet arrays which require machining techniques such as milling or drilling. These techniques must be performed to tight tolerances to ensure accuracy of the B0 field. Furthermore, these systems generally have hand-wound RF or gradient coils that are not trivial to construct. The main goals of this work are to reduce the size of single-sided MRI sensors while simultaneously making them more accessible for others to build. To this end, we present a hand-held, single-sided, MRI sensor that is constructed using an easy-to-assemble magnet array, a 3D-printed housing, and printed circuit boards (PCBs) that contain the RF coil, gradient coils, and matching network. By implementing all coils directly on PCBs, the geometry can be easily optimized and then manufactured at low cost. Both spin density-weighted and T1-weighted images of various samples are presented to demonstrate the capabilities of the proposed sensor.
Collapse
Affiliation(s)
- Mason Greer
- Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, USA.
| | - Cheng Chen
- Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, USA.
| | - Soumyajit Mandal
- Case Western Reserve University, 10900 Euclid Ave, Cleveland, OH 44106, USA.
| |
Collapse
|
29
|
O'Reilly T, Teeuwisse WM, Webb AG. Three-dimensional MRI in a homogenous 27 cm diameter bore Halbach array magnet. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 307:106578. [PMID: 31470234 DOI: 10.1016/j.jmr.2019.106578] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 08/15/2019] [Accepted: 08/16/2019] [Indexed: 06/10/2023]
Abstract
Modern clinical MRI systems utilise very high magnetic fields strengths to produce high resolution images of the human body. The high up-front and maintenance cost of these systems means that much of the world lacks access to this technology. In this paper we propose a low cost, head-only, homogenous Halbach magnet array with the potential for paediatric neuroimaging in low-resource settings. The homogeneity of the Halbach array is improved by allowing the diameter of the Halbach array to vary along its length, and also adding smaller internal shim magnets. The constructed magnet has a bore diameter of 27 cm, mean B0 field strength of 50.4 mT and a homogeneity of 2400 ppm over a 20 cm diameter spherical volume. The level of homogeneity of the system means that coil-based gradients can be used for spatial encoding which greatly increases the flexibility in image acquisition. 3D images of a "brain phantom" were acquired over a 22 × 22 × 22 cm field of view with a 3.5 mm isotropic resolution using a spin-echo sequence. Future development of a low-cost gradient amplifier and an open-source spectrometer has the potential of offering a fully open-source, low-cost MRI system for paediatric neuroimaging in low-resource settings.
Collapse
Affiliation(s)
- T O'Reilly
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - W M Teeuwisse
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands
| | - A G Webb
- C.J. Gorter Center for High Field MRI, Department of Radiology, Leiden University Medical Center, Leiden, the Netherlands.
| |
Collapse
|