1
|
Petzold J, Schmitter S, Silemek B, Winter L, Speck O, Ittermann B, Seifert F. Investigation of alternative RF power limit control methods for 0.5T, 1.5T, and 3T parallel transmission cardiac imaging: A simulation study. Magn Reson Med 2024; 91:1659-1675. [PMID: 38031517 DOI: 10.1002/mrm.29932] [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: 06/27/2023] [Revised: 10/09/2023] [Accepted: 10/31/2023] [Indexed: 12/01/2023]
Abstract
PURPOSE To investigate safety and performance aspects of parallel-transmit (pTx) RF control-modes for a body coil atB 0 ≤ 3 T $$ {B}_0\le 3\mathrm{T} $$ . METHODS Electromagnetic simulations of 11 human voxel models in cardiac imaging position were conducted forB 0 = 0.5 T $$ {B}_0=0.5\mathrm{T} $$ ,1.5 T $$ 1.5\mathrm{T} $$ and3 T $$ 3\mathrm{T} $$ and a body coil with a configurable number of transmit channels (1, 2, 4, 8, 16). Three safety modes were considered: the 'SAR-controlled mode' (SCM), where specific absorption rate (SAR) is limited directly, a 'phase agnostic SAR-controlled mode' (PASCM), where phase information is neglected, and a 'power-controlled mode' (PCM), where the voltage amplitude for each channel is limited. For either mode, safety limits were established based on a set of 'anchor' simulations and then evaluated in 'target' simulations on previously unseen models. The comparison allowed to derive safety factors accounting for varying patient anatomies. All control modes were compared in terms of theB 1 + $$ {B}_1^{+} $$ amplitude and homogeneity they permit under their respective safety requirements. RESULTS Large safety factors (approximately five) are needed if only one or two anchor models are investigated but they shrink with increasing number of anchors. The achievableB 1 + $$ {B}_1^{+} $$ is highest for SCM but this advantage is reduced when the safety factor is included. PCM appears to be more robust against variations of subjects. PASCM performance is mostly in between SCM and PCM. Compared to standard circularly polarized (CP) excitation, pTx offers minorB 1 + $$ {B}_1^{+} $$ improvements if local SAR limits are always enforced. CONCLUSION PTx body coils can safely be used atB 0 ≤ 3 T $$ {B}_0\le 3\mathrm{T} $$ . Uncertainties in patient anatomy must be accounted for, however, by simulating many models.
Collapse
Affiliation(s)
- Johannes Petzold
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Berk Silemek
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Lukas Winter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Oliver Speck
- Biomedical Magnetic Resonance, Otto von Guericke University Magdeburg, Magdeburg, Germany
| | - Bernd Ittermann
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Frank Seifert
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| |
Collapse
|
2
|
Bridgen P, Tomi-Tricot R, Uus A, Cromb D, Quirke M, Almalbis J, Bonse B, De la Fuente Botella M, Maggioni A, Cio PD, Cawley P, Casella C, Dokumaci AS, Thomson AR, Willers Moore J, Bridglal D, Saravia J, Finck T, Price AN, Pickles E, Cordero-Grande L, Egloff A, O’Muircheartaigh J, Counsell SJ, Giles SL, Deprez M, De Vita E, Rutherford MA, Edwards AD, Hajnal JV, Malik SJ, Arichi T. High resolution and contrast 7 tesla MR brain imaging of the neonate. FRONTIERS IN RADIOLOGY 2024; 3:1327075. [PMID: 38304343 PMCID: PMC10830693 DOI: 10.3389/fradi.2023.1327075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/24/2023] [Accepted: 12/29/2023] [Indexed: 02/03/2024]
Abstract
Introduction Ultra-high field MR imaging offers marked gains in signal-to-noise ratio, spatial resolution, and contrast which translate to improved pathological and anatomical sensitivity. These benefits are particularly relevant for the neonatal brain which is rapidly developing and sensitive to injury. However, experience of imaging neonates at 7T has been limited due to regulatory, safety, and practical considerations. We aimed to establish a program for safely acquiring high resolution and contrast brain images from neonates on a 7T system. Methods Images were acquired from 35 neonates on 44 occasions (median age 39 + 6 postmenstrual weeks, range 33 + 4 to 52 + 6; median body weight 2.93 kg, range 1.57 to 5.3 kg) over a median time of 49 mins 30 s. Peripheral body temperature and physiological measures were recorded throughout scanning. Acquired sequences included T2 weighted (TSE), Actual Flip angle Imaging (AFI), functional MRI (BOLD EPI), susceptibility weighted imaging (SWI), and MR spectroscopy (STEAM). Results There was no significant difference between temperature before and after scanning (p = 0.76) and image quality assessment compared favorably to state-of-the-art 3T acquisitions. Anatomical imaging demonstrated excellent sensitivity to structures which are typically hard to visualize at lower field strengths including the hippocampus, cerebellum, and vasculature. Images were also acquired with contrast mechanisms which are enhanced at ultra-high field including susceptibility weighted imaging, functional MRI, and MR spectroscopy. Discussion We demonstrate safety and feasibility of imaging vulnerable neonates at ultra-high field and highlight the untapped potential for providing important new insights into brain development and pathological processes during this critical phase of early life.
Collapse
Affiliation(s)
- Philippa Bridgen
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
| | - Raphael Tomi-Tricot
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MR Research Collaborations, Siemens Healthcare Limited, London, United Kingdom
| | - Alena Uus
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Daniel Cromb
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Megan Quirke
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Jennifer Almalbis
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Beya Bonse
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Miguel De la Fuente Botella
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Alessandra Maggioni
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Pierluigi Di Cio
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
| | - Paul Cawley
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Chiara Casella
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Ayse Sila Dokumaci
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Alice R. Thomson
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
| | - Jucha Willers Moore
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
| | - Devi Bridglal
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Joao Saravia
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Thomas Finck
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Anthony N. Price
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Elisabeth Pickles
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Lucilio Cordero-Grande
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Image Technologies, ETSI Telecomunicación, Universidad Politécnica de Madrid and CIBER-BBN, ISCIII, Madrid, Spain
| | - Alexia Egloff
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Jonathan O’Muircheartaigh
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
- Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, Psychology and Neuroscience, King’s College London, London, United Kingdom
| | - Serena J. Counsell
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Sharon L. Giles
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Maria Deprez
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Enrico De Vita
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MR Physics, Radiology Department, Great Ormond Street Hospital for Children, London, United Kingdom
| | - Mary A. Rutherford
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
| | - A. David Edwards
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
| | - Joseph V. Hajnal
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Shaihan J. Malik
- LondonCollaborative Ultra High Field System (LoCUS), King’s College London, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
| | - Tomoki Arichi
- Guys and St Thomas’ NHS Foundation Trust, London, United Kingdom
- Centre for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King’s College London, London, United Kingdom
- MRC Centre for Neurodevelopmental Disorders, King’s College London, London, United Kingdom
| |
Collapse
|
3
|
van Ooijen I, Annink K, Benders M, Dudink J, Alderliesten T, Groenendaal F, Tataranno M, Lequin M, Hoogduin J, Visser F, Raaijmakers A, Klomp D, Wiegers E, Wijnen J, van der Aa N. Introduction of ultra-high-field MR brain imaging in infants: vital parameters, temperature and comfort. NEUROIMAGE. REPORTS 2023; 3:100175. [PMID: 38357432 PMCID: PMC10865273 DOI: 10.1016/j.ynirp.2023.100175] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 05/19/2023] [Accepted: 05/20/2023] [Indexed: 02/16/2024]
Abstract
Background Brain MRI in infants at ultra-high-field scanners might improve diagnostic quality, but safety should be evaluated first. In our previous study, we reported simulated specific absorption rates and acoustic noise data at 7 Tesla. Methods In this study, we included twenty infants between term-equivalent age and three months of age. The infants were scanned on a 7 Tesla MRI directly after their clinically indicated 3 Tesla brain MRI scan. Vital parameters, temperature, and comfort were monitored throughout the process. Brain temperature was estimated during the MRI scans using proton MR spectroscopy. Results We found no significant differences in vital parameters, temperature, and comfort during and after 7 Tesla MRI scans, compared to 3 Tesla MRI scans. Conclusions These data confirm our hypothesis that scanning infants at 7 Tesla MRI appears to be safe and we identified no additional risks from scanning at 3 Tesla MRI.
Collapse
Affiliation(s)
- I.M. van Ooijen
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - K.V. Annink
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - M.J.N.L. Benders
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - J. Dudink
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - T. Alderliesten
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - F. Groenendaal
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - M.L. Tataranno
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| | - M.H. Lequin
- Departement of Radiology, Division of Imaging and Oncology, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - J.M. Hoogduin
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - F. Visser
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - A.J.E. Raaijmakers
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
- Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands
| | - D.W.J. Klomp
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - E.C. Wiegers
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - J.P. Wijnen
- Centre for Image Sciences, High Field MR Research, University Medical Center Utrecht, University Utrecht, Utrecht, the Netherlands
| | - N.E. van der Aa
- Department of Neonatology, University Medical Center Utrecht, Utrecht Brain Center, University Utrecht, Utrecht, the Netherlands
| |
Collapse
|
4
|
Kopanoglu E. Actual patient position versus safety models: Specific Absorption Rate implications of initial head position for Ultrahigh Field Magnetic Resonance Imaging. NMR IN BIOMEDICINE 2023; 36:e4876. [PMID: 36385447 PMCID: PMC10802886 DOI: 10.1002/nbm.4876] [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: 06/08/2022] [Revised: 10/20/2022] [Accepted: 11/13/2022] [Indexed: 06/16/2023]
Abstract
Specific absorption rate (SAR) relates power absorption to tissue heating, and therefore is used as a safety constraint in magnetic resonance imaging (MRI). This study investigates the implications of initial head positioning on local and whole-head SAR. A virtual body model was simulated at 161 positions inside an eight-channel parallel-transmit (pTx) array. On-axis displacements and rotations of up to 20 mm/degrees and off-axis axial/coronal translations were investigated. Single-channel, radiofrequency (RF) shimming (i.e., single-spoke pTx) and multispoke pTx pulses were designed for seven axial, five coronal and five sagittal slices at each position (the slices were consistent across all positions). Whole-head and local SAR were calculated using safety models consisting of a single (centred) body position, multiple representative positions and all simulated body positions. Positional mismatches between safety models and actual positions cause SAR underestimation. For axial imaging, the actual peak local SAR was up to 4.2-fold higher for both single-channel and 5-spoke pTx, 3.5-fold higher for 3-/4-spoke pTx, and 2-fold higher for RF shimming and 2-spoke pTx, compared with that calculated using the centred body position. For sagittal and coronal imaging, the underestimation of peak local SAR was up to 5.2-fold and 3.8-fold, respectively. Using all body positions to estimate SAR prevented SAR underestimation but yielded up to 11-fold SAR overestimation for RF shimming. Local SAR of single-channel and pTx multispoke pulses showed considerable dependence on the initial patient position. RF shimming yielded much lower sensitivity to positional mismatches for axial imaging but not for sagittal and coronal imaging. This was deemed attributable to the higher degrees-of-freedom of control offered by the investigated coil array for axial imaging. Whole-head SAR is less sensitive to positional mismatches compared with local SAR. Nevertheless, whole-head SAR increased by up to 80% for sagittal imaging. Local and whole-head SAR were observed to be more sensitive to positional mismatches in the axial plane, because of larger variations in coil-tissue proximity. Using all possible body positions in the safety model may become substantially over-conservative and limit imaging performance, especially for the RF shimming mode for axial imaging.
Collapse
Affiliation(s)
- Emre Kopanoglu
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of PsychologyCardiff UniversityCardiffUK
| |
Collapse
|
5
|
Ntolkeras G, Jeong H, Zöllei L, Dmytriw AA, Purvaziri A, Lev MH, Grant PE, Bonmassar G. A high-resolution pediatric female whole-body numerical model with comparison to a male model. Phys Med Biol 2023; 68:10.1088/1361-6560/aca950. [PMID: 36595234 PMCID: PMC10624254 DOI: 10.1088/1361-6560/aca950] [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: 09/01/2022] [Accepted: 12/06/2022] [Indexed: 12/12/2022]
Abstract
Objective. Numerical models are central in designing and testing novel medical devices and in studying how different anatomical changes may affect physiology. Despite the numerous adult models available, there are only a few whole-body pediatric numerical models with significant limitations. In addition, there is a limited representation of both male and female biological sexes in the available pediatric models despite the fact that sex significantly affects body development, especially in a highly dynamic population. As a result, we developed Athena, a realistic female whole-body pediatric numerical model with high-resolution and anatomical detail.Approach. We segmented different body tissues through Magnetic Resonance Imaging (MRI) and Computed Tomography (CT) images of a healthy 3.5 year-old female child using 3D Slicer. We validated the high anatomical accuracy segmentation through two experienced sub-specialty-certified neuro-radiologists and the inter and intra-operator variability of the segmentation results comparing sex differences in organ metrics with physiologic values. Finally, we compared Athena with Martin, a similar male model, showing differences in anatomy, organ metrics, and MRI dosimetric exposure.Main results. We segmented 267 tissue compartments, which included 50 brain tissue labels. The tissue metrics of Athena displayed no deviation from the literature value of healthy children. We show the variability of brain metrics in the male and female models. Finally, we offer an example of computing Specific Absorption Rate and Joule heating in a toddler/preschooler at 7 T MRI.Significance. This study introduces a female realistic high-resolution numerical model using MRI and CT scans of a 3.5 year-old female child, the use of which includes but is not limited to radiofrequency safety studies for medical devices (e.g. an implantable medical device safety in MRI), neurostimulation studies, and radiation dosimetry studies. This model will be open source and available on the Athinoula A. Martinos Center for Biomedical Imaging website.
Collapse
Affiliation(s)
- Georgios Ntolkeras
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Division of Newborn Medicine, Boston Children’s Hospital, Boston, United States of America
- Department of Pediatrics, Baystate Medical Center, Springfield, United States of America
| | - Hongbae Jeong
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, United States of America
| | - Lilla Zöllei
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, United States of America
| | - Adam A Dmytriw
- Department of Radiology, Boston Children’s Hospital, Boston, United States of America
- Department of Radiology, Massachusetts General Hospital, Boston, United States of America
| | - Ali Purvaziri
- Department of Radiology, Massachusetts General Hospital, Boston, United States of America
| | - Michael H Lev
- Department of Radiology, Massachusetts General Hospital, Boston, United States of America
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Division of Newborn Medicine, Boston Children’s Hospital, Boston, United States of America
- Department of Radiology, Boston Children’s Hospital, Boston, United States of America
| | - Giorgio Bonmassar
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, United States of America
| |
Collapse
|
6
|
Seo JH, Jo YS, Oh CH, Chung JY. A New Combination of Radio-Frequency Coil Configurations Using High-Permittivity Materials and Inductively Coupled Structures for Ultrahigh-Field Magnetic Resonance Imaging. SENSORS (BASEL, SWITZERLAND) 2022; 22:8968. [PMID: 36433565 PMCID: PMC9694602 DOI: 10.3390/s22228968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/28/2022] [Revised: 11/03/2022] [Accepted: 11/17/2022] [Indexed: 06/16/2023]
Abstract
In ultrahigh-field (UHF) magnetic resonance imaging (MRI) system, the RF power required to excite the nuclei of the target object increases. As the strength of the main magnetic field (B0 field) increases, the improvement of the RF transmit field (B1+ field) efficiency and receive field (B1- field) sensitivity of radio-frequency (RF) coils is essential to reduce their specific absorption rate and power deposition in UHF MRI. To address these problems, we previously proposed a method to simultaneously improve the B1+ field efficiency and B1- field sensitivity of 16-leg bandpass birdcage RF coils (BP-BC RF coils) by combining a multichannel wireless RF element (MCWE) and segmented cylindrical high-permittivity material (scHPM) comprising 16 elements in 7.0 T MRI. In this work, we further improved the performance of transmit/receive RF coils. A new combination of RF coil with wireless element and HPM was proposed by comparing the BP-BC RF coil with the MCWE and the scHPM proposed in the previous study and the multichannel RF coils with a birdcage RF coil-type wireless element (BCWE) and the scHPM proposed in this study. The proposed 16-ch RF coils with the BCWE and scHPM provided excellent B1+ field efficiency and B1- field sensitivity improvement.
Collapse
Affiliation(s)
- Jeung-Hoon Seo
- Neuroscience Research Institute, Gachon University, Incheon 21988, Republic of Korea
| | - Young-Seung Jo
- Neuroscience Research Institute, Gachon University, Incheon 21988, Republic of Korea
- Department of Electronics and Information Engineering, Korea University, Sejong 30019, Republic of Korea
| | - Chang-Hyun Oh
- Department of Electronics and Information Engineering, Korea University, Sejong 30019, Republic of Korea
| | - Jun-Young Chung
- Department of Neuroscience, College of Medicine, Gachon University, Incheon 21565, Republic of Korea
| |
Collapse
|
7
|
Clément J, Tomi-Tricot R, Malik SJ, Webb A, Hajnal JV, Ipek Ö. Towards an integrated neonatal brain and cardiac examination capability at 7 T: electromagnetic field simulations and early phantom experiments using an 8-channel dipole array. MAGMA (NEW YORK, N.Y.) 2022; 35:765-778. [PMID: 34997396 PMCID: PMC9463228 DOI: 10.1007/s10334-021-00988-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 12/06/2021] [Accepted: 12/06/2021] [Indexed: 11/27/2022]
Abstract
OBJECTIVE Neonatal brain and cardiac imaging would benefit from the increased signal-to-noise ratio levels at 7 T compared to lower field. Optimal performance might be achieved using purpose designed RF coil arrays. In this study, we introduce an 8-channel dipole array and investigate, using simulations, its RF performances for neonatal applications at 7 T. METHODS The 8-channel dipole array was designed and evaluated for neonatal brain/cardiac configurations in terms of SAR efficiency (ratio between transmit-field and maximum specific-absorption-rate level) using adjusted dielectric properties for neonate. A birdcage coil operating in circularly polarized mode was simulated for comparison. Validation of the simulation model was performed on phantom for the coil array. RESULTS The 8-channel dipole array demonstrated up to 46% higher SAR efficiency levels compared to the birdcage coil in neonatal configurations, as the specific-absorption-rate levels were alleviated. An averaged normalized root-mean-square-error of 6.7% was found between measured and simulated transmit field maps on phantom. CONCLUSION The 8-channel dipole array design integrated for neonatal brain and cardiac MR was successfully demonstrated, in simulation with coverage of the baby and increased SAR efficiency levels compared to the birdcage. We conclude that the 8Tx-dipole array promises safe operating procedures for MR imaging of neonatal brain and heart at 7 T.
Collapse
Affiliation(s)
- Jérémie Clément
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK
| | | | - Shaihan J Malik
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, King's College London, London, UK
| | - Andrew Webb
- Department of Radiology, C. J Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, The Netherlands
| | - Joseph V Hajnal
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.,Centre for the Developing Brain, King's College London, London, UK
| | - Özlem Ipek
- Department of Biomedical Engineering, School of Biomedical Engineering and Imaging Sciences, King's College London, London, UK.
| |
Collapse
|
8
|
Malik SJ, Hand JW, Carmichael DW, Hajnal JV. Evaluation of specific absorption rate and heating in children exposed to a 7T MRI head coil. Magn Reson Med 2022; 88:1434-1449. [PMID: 35666836 PMCID: PMC9328145 DOI: 10.1002/mrm.29283] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 03/25/2022] [Accepted: 04/13/2022] [Indexed: 11/27/2022]
Abstract
PURPOSE To evaluate specific absorption rate (SAR) and temperature distributions resulting from pediatric exposure to a 7T head coil. METHODS Exposure from a 297-MHz birdcage head transmit coil (CP mode single-channel transmission) was simulated in several child models (ages 3-14, mass 13.9-50.4 kg) and one adult, using time-domain electromagnetic and thermal solvers. Position variability, age-related changes in dielectric properties, and differences in thermoregulation were also considered. RESULTS Age-adjusted dielectric properties had little effect in this population. Head average SAR (hdSAR) was the limiting factor for all models centered in the coil. The value of hdSAR (normalized to net power) was found to decrease linearly with increasing mass (R2 = 0.86); no equivalent relationship for peak-spatial 10g averaged SAR (psSAR10g ) was identified. Relatively small (< 10%) variability was observed in hdSAR for position shifts of ±25 mm in each orthogonal direction when normalized to net power; accounting for B1+$$ {\mathrm{B}}_1^{+} $$ efficiency can lead to much larger variability. Position sensitivity of psSAR10g was greater, but in most cases hdSAR remained the limiting quantity. For thermal simulations, if blood temperature is fixed (i.e., asserting good thermoregulation), maximum temperatures are compliant with International Electrotechnical Commission limits during 60-min exposure at the SAR limit. Introducing variable blood temperature leads to core temperature changes proportional to whole-body averaged SAR, exceeding guideline limits for all child models. CONCLUSIONS Children experienced higher SAR than adults for the 297-MHz head transmit coil examined in this work. Thermal simulations suggest that core temperature changes could occur in smaller subjects, although experimental data are needed for validation.
Collapse
Affiliation(s)
- Shaihan J Malik
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK.,Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK
| | - Jeffrey W Hand
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK
| | - David W Carmichael
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK
| | - Joseph V Hajnal
- Biomedical Engineering Department, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK.,Center for the Developing Brain, School of Biomedical Engineering and Imaging Sciences, King's College London, St. Thomas' Hospital, London, UK
| |
Collapse
|
9
|
Seo JH, Chung JY. A Preliminary Study for Reference RF Coil at 11.7 T MRI: Based on Electromagnetic Field Simulation of Hybrid-BC RF Coil According to Diameter and Length at 3.0, 7.0 and 11.7 T. SENSORS 2022; 22:s22041512. [PMID: 35214409 PMCID: PMC8875900 DOI: 10.3390/s22041512] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/12/2022] [Revised: 02/13/2022] [Accepted: 02/14/2022] [Indexed: 02/05/2023]
Abstract
Magnetic resonance imaging (MRI) systems must undergo quantitative evaluation through daily and periodic performance assessments. In general, the reference or standard radiofrequency (RF) coils for these performance assessments of 1.5 to 7.0 T MRI systems have been low-pass-type birdcage (LP-BC) RF coils. However, LP-BC RF coils are inappropriate for use as reference RF coils because of their relatively lower magnetic field (B1-field) sensitivity than other types of BC RF coils, especially in ultrahigh-field (UHF) MRI systems above 3.0 T. Herein, we propose a hybrid-type BC (Hybrid-BC) RF coil as a reference RF coil with improved B1-field sensitivity in UHF MRI system and applied it to an 11.7 T MRI system. An electromagnetic field (EM-field) analysis on the Hybrid-BC RF coil was performed to provide the proper dimensions for its use as a reference RF coil. Commercial finite difference time-domain program was used in EM-field simulation, and home-made analysis programs were used in analysis. The optimal specifications of the proposed Hybrid-BC RF coils for them to qualify as reference RF coils are proposed based on their B1+-field sensitivity under unnormalized conditions, as well as by considering their B1+-field uniformity and RF safety under normalized conditions.
Collapse
Affiliation(s)
- Jeung-Hoon Seo
- Neuroscience Research Institute, Gachon University, Incheon 21988, Korea;
| | - Jun-Young Chung
- Department of Neuroscience, College of Medicine, Gachon University, Incheon 21565, Korea
- Correspondence: ; Tel.: +82-32-822-5361; Fax: +82-32-822-8251
| |
Collapse
|
10
|
Abstract
After introduction of the first human 7 tesla (7T) system in 1999, 7T MR systems have been employed as one of the most advanced platforms for human MR research for more than 20 years. Currently, two 7T MR models are approved for clinical use in the U.S.A. The approval facilitated introduction of the 7T system, summing up to around 100 worldwide. The approval in Japan is much awaited. As a clinical MR scanner, the 7T MR system is drawing attention in terms of safety.Several large-sized studies on bioeffects have been reported for vertigo, dizziness, motion disturbances, nausea, and others. Such effects might also be found in MR workers and researchers. Frequency and severity of reported bioeffects will be presented and discussed, including their variances. The high resonance frequency and shorter RF wavelength of 7T increase the concern about the safety. Homogeneous RF pulse excitation is difficult even for the brain, and a multi-channel parallel transmit (pTx) system is considered mandatory. However, pTx may create a hot spot, which makes the estimation of specific absorption rate (SAR) to be difficult. The stronger magnetic field of 7T causes a large force of displacement and heating on metallic implants or devices, and the scan of patients with them should not be conducted at 7T. However, there are some opinions that such patients might be scanned even at 7T, if certain criteria are met. This article provides a brief review on the effect of the static magnetic field on humans (MR subjects, workers, and researchers) and neurons, in addition to scan sound, SAR, and metal implants and devices. Understanding and avoiding adverse effects will contribute to the reduction in safety risks and the prevention of incidents.
Collapse
Affiliation(s)
- Tomohisa Okada
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Thai Akasaka
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Dinh Hd Thuy
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| | - Tadashi Isa
- Human Brain Research Center, Graduate School of Medicine, Kyoto University
| |
Collapse
|