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Zhong N, Mi Q, Lu M, Jiang H, Zhang Y. Evaluation of twin fetal exposure to radiofrequency field during magnetic resonance imaging. RADIATION PROTECTION DOSIMETRY 2024; 200:791-801. [PMID: 38777801 DOI: 10.1093/rpd/ncae119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 02/17/2024] [Accepted: 04/14/2024] [Indexed: 05/25/2024]
Abstract
Fetal development is essential to the human lifespan. As more and more multifetal gestations have been reported recently, clinical diagnosis using magnetic resonance imaging (MRI), which introduced radiofrequency (RF) exposure, raised public concerns. The present study developed two whole-body pregnant models of 31 and 32 gestational weeks (GWs) with twin fetuses and explored RF exposure by 1.5 and 3.0 T MRI. Differences in the relative position of the fetus and changes in fetal weight can cause differences in fetal peak local specific absorption rate averaged over 10 g tissue (pSAR10g). Variation of pSAR10g due to different fetal positions can be ~35%. Numerically, twin and singleton fetal pSAR10g results were not significantly different, however twin results exceeded the limit in some cases (e.g. fetuses of 31 GW at 1.5 T), which indicated the necessity for further research employing anatomically correct twin-fetal models coming from various GWs and particular sequence to be applied.
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Affiliation(s)
- Nan Zhong
- China Academy of Information and Communications Technology, No. 52 Huayuanbei Road, Haidian District, Beijing 100191, China
| | - Qunzheng Mi
- China Academy of Information and Communications Technology, No. 52 Huayuanbei Road, Haidian District, Beijing 100191, China
| | - Meng Lu
- China Academy of Information and Communications Technology, No. 52 Huayuanbei Road, Haidian District, Beijing 100191, China
| | - Haoyu Jiang
- China Academy of Information and Communications Technology, No. 52 Huayuanbei Road, Haidian District, Beijing 100191, China
| | - Yi Zhang
- China Academy of Information and Communications Technology, No. 52 Huayuanbei Road, Haidian District, Beijing 100191, China
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2
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Lin J, Li J, Ding G. Absorption of 5G sub-6 GHz electromagnetic radiation from base station to male reproduction system. Int J Radiat Biol 2024; 100:1085-1092. [PMID: 38709715 DOI: 10.1080/09553002.2024.2347354] [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: 09/18/2023] [Accepted: 04/14/2024] [Indexed: 05/08/2024]
Abstract
BACKGROUND The impact of electromagnetic radiation from communication on the male reproductive system has emerged as a significant concern in public health. A notable distinction of the 5G sub-6 GHz band, compared to traditional 2G, 3G, and 4G frequency bands, is the inclusion of higher frequency bands. This has raised public concerns regarding the potential effects of these higher frequencies on organisms, particularly their reproductive systems. While it is imperative to investigate the biological effects and potential risks associated with these new frequency bands in laboratory settings, comparing and evaluating differences between various frequency bands remain challenging due to the absence of standardized parameters such as exposure conditions and duration. In contrast, dose assessment offers a simpler and more reliable approach. MATERIALS AND METHODS The dose assessment method was employed in this study to investigate the risks associated with sub-6 GHz electromagnetic radiation from 5G base stations on the male reproductive system. A classical human body model (Duke) was utilized, and an electromagnetic simulation environment was established based on the actual polarization direction of the exposed base stations and various body postures. This research explored the effects of field direction, posture, public population, and frequency on the specific absorption rate of the reproductive system. RESULTS AND CONCLUSIONS While maintaining the same level of exposure, a higher frequency results in a reduced dosage on reproductive system. Further analysis reveals that, considering the public exposure threshold, the employment of higher frequency bands in 5G sub-6 GHz does not present a greater dosage on reproductive system compared to lower frequency bands. Consequently, with regard to dosage, there is no need for excessive concern among the general public regarding the impact of electromagnetic radiation emitted by 5G base stations operating below 6 GHz on male reproductive health.
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Affiliation(s)
- Jiajin Lin
- Department of Radiation Protection Medicine, School of Military Preventive Medicine, Air Force Medical University, Xi'an, China
- Ministry of Education Key Lab of Hazard Assessment and Control in Special Operational Environment, Xi'an, China
| | - Jing Li
- Department of Radiation Protection Medicine, School of Military Preventive Medicine, Air Force Medical University, Xi'an, China
- Ministry of Education Key Lab of Hazard Assessment and Control in Special Operational Environment, Xi'an, China
| | - Guirong Ding
- Department of Radiation Protection Medicine, School of Military Preventive Medicine, Air Force Medical University, Xi'an, China
- Ministry of Education Key Lab of Hazard Assessment and Control in Special Operational Environment, Xi'an, China
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3
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Yetisir F, Abaci Turk E, Adalsteinsson E, Wald LL, Grant PE. Local SAR management strategies to use two-channel RF shimming for fetal MRI at 3 T. Magn Reson Med 2024; 91:1165-1178. [PMID: 37929768 PMCID: PMC10843691 DOI: 10.1002/mrm.29913] [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: 07/12/2023] [Revised: 10/10/2023] [Accepted: 10/16/2023] [Indexed: 11/07/2023]
Abstract
PURPOSE This study evaluates the imaging performance of two-channel RF-shimming for fetal MRI at 3 T using four different local specific absorption rate (SAR) management strategies. METHODS Due to the ambiguity of safe local SAR levels for fetal MRI, local SAR limits for RF shimming were determined based on either each individual's own SAR levels in standard imaging mode (CP mode) or the maximum SAR level observed across seven pregnant body models in CP mode. Local SAR was constrained either indirectly by further constraining the whole-body SAR (wbSAR) or directly by using subject-specific local SAR models. Each strategy was evaluated by the improvement of the transmit field efficiency (average |B1 + |) and nonuniformity (|B1 + | variation) inside the fetus compared with CP mode for the same wbSAR. RESULTS Constraining wbSAR when using RF shimming decreases B1 + efficiency inside the fetus compared with CP mode (by 12%-30% on average), making it inefficient for SAR management. Using subject-specific models with SAR limits based on each individual's own CP mode SAR value, B1 + efficiency and nonuniformity are improved on average by 6% and 13% across seven pregnant models. In contrast, using SAR limits based on maximum CP mode SAR values across seven models, B1 + efficiency and nonuniformity are improved by 13% and 25%, compared with the best achievable improvement without SAR constraints: 15% and 26%. CONCLUSION Two-channel RF-shimming can safely and significantly improve the transmit field inside the fetus when subject-specific models are used with local SAR limits based on maximum CP mode SAR levels in the pregnant population.
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Affiliation(s)
- Filiz Yetisir
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children’s Hospital, Boston, MA, USA
| | - Esra Abaci Turk
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children’s Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
| | - Elfar Adalsteinsson
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Lawrence L. Wald
- Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - P. Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children’s Hospital, Boston, MA, USA
- Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA
- Department of Radiology, Harvard Medical School, Boston, MA, USA
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4
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Guryev GD, Milshteyn E, Giannakopoulos II, Lattanzi R, Wald LL, Adalsteinsson E, White JK. MARIE 2.0: A Perturbation Matrix Based Patient-Specific MRI Field Simulator. IEEE Trans Biomed Eng 2023; 70:1575-1586. [PMID: 36383593 PMCID: PMC10689076 DOI: 10.1109/tbme.2022.3222748] [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] [Indexed: 11/18/2022]
Abstract
High static field MR scanners can produce human tissue images of astounding clarity, but rely on high frequency electromagnetic radiation that generates complicated in-tissue field patterns that are patient-specific and potentially harmful. Many such scanners use parallel transmitters to better control field patterns, but then adjust the transmitters based on general guidelines rather than optimizing for the specific patient, mostly because computing patient-specific fields was presumed far too slow. It was recently demonstrated that the combination of fast low-resolution tissue mapping and fast voxel-based field simulation can be used to perform a patient-specific MR safety check in minutes. However, the field simulation required several of those minutes, making it too slow to perform the dozens of simulations that would be needed for patient-specific optimization. In this paper we describe a compressed-perturbation-matrix technique that nearly eliminates the computational cost of including complex coils (or coils and shields) in voxel-based field simulation of tissue, thereby reducing simulation time from minutes to seconds. The approach is demonstrated on a wide variety of head+coil and head+coil+shield configurations, using the implementation in MARIE 2.0, the latest version of the open-source MR field simulator MARIE.
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Machado-Rivas F, Cortes-Albornoz MC, Afacan O, Bedoya MA, Calixto C, Choi JJ, Ruggiero M, Gholipour A, Jaimes C. Fetal MRI at 3 T: Principles to Optimize Success. Radiographics 2023; 43:e220141. [PMID: 36995947 PMCID: PMC10091224 DOI: 10.1148/rg.220141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 08/08/2022] [Accepted: 08/10/2022] [Indexed: 03/31/2023]
Abstract
Fetal MRI has emerged as a cornerstone of prenatal imaging, helping to establish the correct diagnosis in pregnancies affected by congenital anomalies. In the past decade, 3 T imaging was introduced as an alternative to increase the signal-to-noise ratio (SNR) of the pulse sequences and improve anatomic detail. However, imaging at a higher field strength is not without challenges. Many artifacts that are barely appreciable at 1.5 T are amplified at 3 T. A systematic approach to imaging at 3 T that incorporates appropriate patient positioning, a thoughtful protocol design, and sequence optimization minimizes the impact of these artifacts and allows radiologists to reap the benefits of the increased SNR. The sequences used are the same at both field strengths and include single-shot T2-weighted, balanced steady-state free-precession, three-dimensional T1-weighted spoiled gradient-echo, and echo-planar imaging. Synergistic use of these acquisitions to sample various tissue contrasts and in various planes provides valuable information about fetal anatomy and pathologic conditions. In the authors' experience, fetal imaging at 3 T outperforms imaging at 1.5 T for most indications when performed under optimal circumstances. The authors condense the cumulative experience of fetal imaging specialists and MRI technologists who practice at a large referral center into a guideline covering all major aspects of fetal MRI at 3 T, from patient preparation to image interpretation. © RSNA, 2023 Quiz questions for this article are available in the supplemental material.
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Affiliation(s)
- Fedel Machado-Rivas
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Maria Camila Cortes-Albornoz
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Onur Afacan
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Maria Alejandra Bedoya
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Camilo Calixto
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Jungwhan John Choi
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Matthew Ruggiero
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Ali Gholipour
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
| | - Camilo Jaimes
- From the Department of Radiology, Boston Children’s Hospital,
300 Longwood Ave, Boston, MA 02215 (F.M.R., M.C.C.A., O.A., M.A.B., C.C., M.R.,
A.G., C.J.); Department of Radiology, Harvard Medical School, Boston, Mass
(J.J.C.); and Department of Radiology, Cincinnati Children’s Hospital,
Cincinnati, Ohio (F.M.R., M.C.C.A., O.A., M.A.B., C.C., A.G., C.J.)
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Abaci Turk E, Stout JN, Feldman HA, Gagoski B, Zhou C, Tamen R, Manhard MK, Adalsteinsson E, Roberts DJ, Golland P, Grant PE, Barth WH. Change in T2* measurements of placenta and fetal organs during Braxton Hicks contractions. Placenta 2022; 128:69-71. [PMID: 36087451 PMCID: PMC9674925 DOI: 10.1016/j.placenta.2022.08.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 08/18/2022] [Accepted: 08/24/2022] [Indexed: 11/15/2022]
Abstract
Maternal-placental perfusion can be temporarily compromised by Braxton Hicks (BH) uterine contractions. Although prior studies have employed T2* changes to investigate the effect of BH contractions on placental oxygen, the effect of these contractions on the fetus has not been fully characterized. We investigated the effect of BH contractions on quantitative fetal organ T2* across gestation together with the birth information. We observed a slight but significant decrease in fetal brain and liver T2* during contractions.
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Affiliation(s)
- Esra Abaci Turk
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
| | - Jeffrey N Stout
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Henry A Feldman
- Institutional Centers for Clinical and Translational Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Borjan Gagoski
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Cindy Zhou
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Rubii Tamen
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - Mary Katherine Manhard
- Department of Radiology,Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA
| | - Elfar Adalsteinsson
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA; Harvard-MIT Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA
| | | | - Polina Golland
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA; Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA; Computer Science and Artificial Intelligence Laboratory (CSAIL), Massachusetts Institute of Technology, Cambridge, MA, USA
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Harvard Medical School, Boston, MA, USA
| | - William H Barth
- Maternal-Fetal Medicine, Obstetrics and Gynecology, Massachusetts General Hospital, Boston, MA, USA
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7
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Knapp J, Tavares de Sousa M, Schönnagel BP. Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives. ROFO-FORTSCHR RONTG 2022; 194:841-851. [PMID: 35905903 DOI: 10.1055/a-1761-3500] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
BACKGROUND Fetal magnetic resonance imaging (MRI) has become a valuable adjunct to ultrasound in the prenatal diagnosis of congenital pathologies of the central nervous system, thorax, and abdomen. Fetal cardiovascular magnetic resonance (CMR) was limited, mainly by the lack of cardiac gating, and has only recently evolved due to technical developments. METHOD A literature search was performed on PubMed, focusing on technical advancements to perform fetal CMR. In total, 20 publications on cardiac gating techniques in the human fetus were analyzed. RESULTS Fetal MRI is a safe imaging method with no developmental impairments found to be associated with in utero exposure to MRI. Fetal CMR is challenging due to general drawbacks (e. g., fetal motion) and specific limitations such as the difficulty to generate a cardiac gating signal to achieve high spatiotemporal resolution. Promising technical advancements include new methods for fetal cardiac gating, based on novel post-processing approaches and an external hardware device, as well as motion compensation and acceleration techniques. CONCLUSION Newly developed direct and indirect gating approaches were successfully applied to achieve high-quality morphologic and functional imaging as well as quantitative assessment of fetal hemodynamics in research settings. In cases when prenatal echocardiography is limited, e. g., by an unfavorable fetal position in utero, or when its results are inconclusive, fetal CMR could potentially serve as a valuable adjunct in the prenatal assessment of congenital cardiovascular malformations. However, sufficient data on the diagnostic performance and clinical benefit of new fetal CMR techniques is still lacking. KEY POINTS · New fetal cardiac gating methods allow high-quality fetal CMR.. · Motion compensation and acceleration techniques allow for improvement of image quality.. · Fetal CMR could potentially serve as an adjunct to fetal echocardiography in the future.. CITATION FORMAT · Knapp J, Tavares de Sousa M, Schönnagel BP. Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives. Fortschr Röntgenstr 2022; 194: 841 - 851.
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Affiliation(s)
- Janine Knapp
- Diagnostic and Interventional Radiology and Nuclear Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | | | - Björn P Schönnagel
- Diagnostic and Interventional Radiology and Nuclear Medicine, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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8
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Stout JN, Bedoya MA, Grant PE, Estroff JA. Fetal Neuroimaging Updates. Magn Reson Imaging Clin N Am 2021; 29:557-581. [PMID: 34717845 PMCID: PMC8562558 DOI: 10.1016/j.mric.2021.06.007] [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] [Indexed: 11/29/2022]
Abstract
MR imaging is used in conjunction with ultrasound screening for fetal brain abnormalities because it offers better contrast, higher resolution, and has multiplanar capabilities that increase the accuracy and confidence of diagnosis. Fetal motion still severely limits the MR imaging sequences that can be acquired. We outline the current acquisition strategies for fetal brain MR imaging and discuss the near term advances that will improve its reliability. Prospective and retrospective motion correction aim to make the complement of MR neuroimaging modalities available for fetal diagnosis, improve the performance of existing modalities, and open new horizons to understanding in utero brain development.
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Affiliation(s)
- Jeffrey N Stout
- Fetal and Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA.
| | - M Alejandra Bedoya
- Department of Radiology, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
| | - P Ellen Grant
- Fetal and Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA; Department of Radiology, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA; Department of Pediatrics, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
| | - Judy A Estroff
- Department of Radiology, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA; Maternal Fetal Care Center, Boston Children's Hospital, 300 Longwood Avenue, Boston, MA 02115, USA
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9
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Yetisir F, Abaci Turk E, Guerin B, Gagoski BA, Grant PE, Adalsteinsson E, Wald LL. Safety and imaging performance of two-channel RF shimming for fetal MRI at 3T. Magn Reson Med 2021; 86:2810-2821. [PMID: 34240759 DOI: 10.1002/mrm.28895] [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: 04/23/2021] [Revised: 05/31/2021] [Accepted: 06/02/2021] [Indexed: 11/07/2022]
Abstract
PURPOSE This study investigates whether two-channel radiofrequency (RF) shimming can improve imaging without increasing specific absorption rate (SAR) for fetal MRI at 3T. METHODS Transmit field ( B 1 + ) average and variation in the fetus was simulated in seven numerical pregnant body models. Safety was quantified by maternal and fetal peak local SAR and fetal average SAR. The shim parameter space was divided into improved B 1 + (magnitude and homogeneity) and improved SAR regions, and an overlap where RF shimming improved both classes of metrics compared with birdcage mode was assessed. Additionally, the effect of fetal position, tissue detail, and dielectric properties on transmit field and SAR was studied. RESULTS A region of subject-specific RF shim parameter space improving both B 1 + and SAR metrics was found for five of the seven models. Optimizing only B 1 + metrics improved B 1 + efficiency across models by 15% on average and 28% for the best-case model. B 1 + variation improved by 26% on average and 49% for the best case. However, for these shim settings, fetal SAR increased by up to 106%. The overlap region, where both B 1 + and SAR metrics improve, showed an average B 1 + efficiency improvement of 6% on average across models and 19% for the best-case model. B 1 + variation improved by 13% on average and 40% for the best case. RFS could also decrease maternal/fetal SAR by up to 49%/58%. CONCLUSION RF shimming can improve imaging compared with birdcage mode without increasing fetal and maternal SAR when a patient-specific SAR model is incorporated into the shimming procedure.
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Affiliation(s)
- Filiz Yetisir
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, Massachusetts, USA
| | - Esra Abaci Turk
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, Massachusetts, USA
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
| | - Bastien Guerin
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Borjan A Gagoski
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, Massachusetts, USA
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA
| | - P Ellen Grant
- Fetal-Neonatal Neuroimaging & Developmental Science Center, Boston Children's Hospital, Boston, Massachusetts, USA
- Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA
| | - Elfar Adalsteinsson
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Lawrence L Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA
- Department of Radiology, Harvard Medical School, Boston, Massachusetts, USA
- Harvard-MIT Division of Health Sciences and Technology, Cambridge, Massachusetts, USA
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10
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Machado-Rivas F, Jaimes C, Kirsch JE, Gee MS. Image-quality optimization and artifact reduction in fetal magnetic resonance imaging. Pediatr Radiol 2020; 50:1830-1838. [PMID: 33252752 DOI: 10.1007/s00247-020-04672-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Revised: 03/09/2020] [Accepted: 03/31/2020] [Indexed: 11/28/2022]
Abstract
Fetal MRI allows for earlier and better detection of complex congenital anomalies. However, its diagnostic utility is often limited by technical barriers that introduce artifacts and reduce image quality. The main determinants of fetal MR image quality are speed of acquisition, spatial resolution and signal-to-noise ratio (SNR). Imaging optimization is a challenge because a change to improve one scan parameter often leads to worsening of another. Moreover, the recent introduction of fetal MRI on 3-tesla (T) scanners to achieve better SNR can amplify some technical issues. Motion, banding artifacts and aliasing artifacts impact the quality of fetal acquisitions at any field strength. High specific absorption rate (SAR) and artifacts from inhomogeneities in the radiofrequency field are important limitations of high-field-strength imaging. We discuss technical barriers that impact image quality and are important limitations to prenatal MRI diagnosis, and propose solutions to improve image quality and reduce artifacts.
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Affiliation(s)
- Fedel Machado-Rivas
- Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Camilo Jaimes
- Department of Radiology, Harvard Medical School, Boston, MA, USA.,Department of Radiology, Boston Children's Hospital, Boston, MA, USA
| | - John E Kirsch
- Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston, MA, 02114, USA.,Department of Radiology, Harvard Medical School, Boston, MA, USA
| | - Michael S Gee
- Department of Radiology, Massachusetts General Hospital, 55 Fruit St., Boston, MA, 02114, USA. .,Department of Radiology, Harvard Medical School, Boston, MA, USA.
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Abstract
MRI is a powerful diagnostic tool with excellent soft tissue contrast that uses nonionizing radiation. These advantages make MRI an appealing modality for imaging the pregnant patient; however, specific risks inherent to the magnetic resonance environment must be considered. MRI may be performed without and/or with intravenous contrast, which adds further fetal considerations. The risks of MRI with and without intravenous contrast are reviewed as they pertain to the pregnant or lactating patient and to the fetus and nursing infant. Relevant issues for gadolinium-based contrast agents and ultrasmall paramagnetic iron oxide particles are reviewed.
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Affiliation(s)
- Jason T Little
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Candice A Bookwalter
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA.
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12
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Milshteyn E, Guryev G, Torrado-Carvajal A, Adalsteinsson E, White JK, Wald LL, Guerin B. Individualized SAR calculations using computer vision-based MR segmentation and a fast electromagnetic solver. Magn Reson Med 2020; 85:429-443. [PMID: 32643152 DOI: 10.1002/mrm.28398] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 04/28/2020] [Accepted: 06/05/2020] [Indexed: 11/06/2022]
Abstract
PURPOSE We propose a fast, patient-specific workflow for on-line specific absorption rate (SAR) supervision. An individualized electromagnetic model is created while the subject is on the table, followed by rapid SAR estimates for that individual. Our goal is an improved correspondence between the patient and model, reducing reliance on general anatomical body models. METHODS A 3D fat-water 3T acquisition (~2 minutes) is automatically segmented using a computer vision algorithm (~1 minute) into what we found to be the most important electromagnetic tissue classes: air, bone, fat, and soft tissues. We then compute the individual's EM field exposure and global and local SAR matrices using a fast electromagnetic integral equation solver. We assess the approach in 10 volunteers and compare to the SAR seen in a standard generic body model (Duke). RESULTS The on-the-table workflow averaged 7'44″. Simulation of the simplified Duke models confirmed that only air, bone, fat, and soft tissue classes are needed to estimate global and local SAR with an error of 6.7% and 2.7%, respectively, compared to the full model. In contrast, our volunteers showed a 16.0% and 20.3% population variability in global and local SAR, respectively, which was mostly underestimated by the Duke model. CONCLUSION Timely construction and deployment of a patient-specific model is computationally feasible. The benefit of resolving the population heterogeneity compared favorably to the modest modeling error incurred. This suggests that individualized SAR estimates can improve electromagnetic safety in MRI and possibly reduce conservative safety margins that account for patient-model mismatch, especially in non-standard patients.
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Affiliation(s)
- Eugene Milshteyn
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA.,Harvard Medical School, Boston, MA, USA
| | - Georgy Guryev
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Angel Torrado-Carvajal
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA.,Harvard Medical School, Boston, MA, USA.,Medical Image Analysis and Biometry Laboratory, Universidad Rey Juan Carlos, Madrid, Spain
| | - Elfar Adalsteinsson
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA.,Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, MA, USA.,Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, USA
| | - Jacob K White
- Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Lawrence L Wald
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA.,Harvard Medical School, Boston, MA, USA.,Harvard-MIT Division of Health Sciences Technology, Cambridge, MA, USA
| | - Bastien Guerin
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USA.,Harvard Medical School, Boston, MA, USA
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