51
|
Tang M, Yamamoto T. Progress in Understanding Radiofrequency Heating and Burn Injuries for Safer MR Imaging. Magn Reson Med Sci 2022; 22:7-25. [PMID: 35228437 PMCID: PMC9849420 DOI: 10.2463/mrms.rev.2021-0047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
RF electromagnetic wave exposure during MRI scans induces heat and occasionally causes burn injuries to patients. Among all the types of physical injuries that have occurred during MRI examinations, RF burn injuries are the most common ones. The number of RF burn injuries increases as the static magnetic field of MRI systems increases because higher RFs lead to higher heating. The commonly believed mechanisms of RF burn injuries are the formation of a conductive loop by the patient's posture or cables, such as an electrocardiogram lead; however, the mechanisms of RF burn injuries that occur at the contact points, such as the bore wall and the elbow, remain unclear. A comprehensive understanding of RF heating is needed to address effective countermeasures against all RF burn injuries for safe MRI examinations. In this review, we summarize the occurrence of RF burn injury cases by categorizing RF burn injuries reported worldwide in recent decades. Safety standards and regulations governing RF heating that occurs during MRI examinations are presented, along with their theoretical and physiological backgrounds. The experimental assessment techniques for RF heating are then reviewed, and the development of numerical simulation techniques is explained. In addition, a comprehensive theoretical interpretation of RF burn injuries is presented. By including the results of recent experimental and numerical simulation studies on RF heating, this review describes the progress achieved in understanding RF heating from the standpoint of MRI burn injury prevention.
Collapse
Affiliation(s)
- Minghui Tang
- Department of Diagnostic Imaging, Faculty of Medicine and Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido, Japan
| | - Toru Yamamoto
- Division of Biomedical Engineering and Science, Faculty of Health Sciences, Hokkaido University, Sapporo, Hokkaido, Japan,Corresponding author: Faculty of Health Sciences, Hokkaido University, Kita 12 Nishi 5, Kita-ku, Sapporo, Hokkaido 060-0812, Japan. Phone: +81-11-706-3412, Fax: +81-11-706-4916, E-mail:
| |
Collapse
|
52
|
Colella M, Biscarini M, de Meis M, Patrizi R, Ciallella T, Ferrante D, De Gaetano A, Capuano M, Pellegrino G, Martini E, Cavagnaro M, Apollonio F, Liberti M. Numerical Evaluation of Human Body Near Field Exposure to a Vehicular Antenna for Military Applications. Front Public Health 2022; 9:794564. [PMID: 35186873 PMCID: PMC8851057 DOI: 10.3389/fpubh.2021.794564] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2021] [Accepted: 12/31/2021] [Indexed: 12/23/2022] Open
Abstract
Background The use of electromagnetic (EM) technologies for military applications is gaining increasing interest to satisfy different operational needs, such as improving battlefield communications or jamming counterpart's signals. This is achieved by the use of high-power EM waves in several frequency bands (e.g., HF, VHF, and UHF). When considering military vehicles, several antennas are present in close proximity to the crew personnel, which are thus potentially exposed to high EM fields. Methods A typical exposure scenario was reproduced numerically to evaluate the EM exposure of the human body in the presence of an HF vehicular antenna (2–30 MHz). The antenna was modeled as a monopole connected to a 3D polygonal structure representing the vehicle. Both the EM field levels in the absence and in the presence of the human body and also the specific absorption rate (SAR) values were calculated. The presence of the operator, partially standing outside the vehicle, was simulated with the virtual human body model Duke (Virtual Population, V.3). Several exposure scenarios were considered. The presence of a protective helmet was modeled as well. Results In the area usually occupied by the personnel, E-field intensity radiated by the antenna can reach values above the limits settled by international safety guidelines. Nevertheless, local SAR values induced inside the human body reached a maximum value of 14 mW/kg, leading to whole-body averaged and 10-g averaged SAR values well below the corresponding limits. Conclusion A complex and realistic near-field exposure scenario of the crew of a military vehicle was simulated. The obtained E-field values radiated in the free space by a HF vehicular antenna may reach values above the safety guidelines reference levels. Such values are not necessarily meaningful for the exposed subject. Indeed, SAR and E-field values induced inside the body remain well below safety limits.
Collapse
Affiliation(s)
- Micol Colella
- Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
| | - Marianna Biscarini
- Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
| | | | | | | | - Daniele Ferrante
- Centro Polifunzionale di Sperimentazione (CEPOLISPE), Rome, Italy
| | | | - Marco Capuano
- Centro Polifunzionale di Sperimentazione (CEPOLISPE), Rome, Italy
| | | | - Emanuele Martini
- Centro Polifunzionale di Sperimentazione (CEPOLISPE), Rome, Italy
| | - Marta Cavagnaro
- Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
| | - Francesca Apollonio
- Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
| | - Micaela Liberti
- Department of Information Engineering, Electronics and Telecommunications, Sapienza University of Rome, Rome, Italy
- *Correspondence: Micaela Liberti
| |
Collapse
|
53
|
Torchio R, Arduino A, Zilberti L, Bottauscio O. A fast tool for the parametric analysis of human body exposed to LF electromagnetic fields in biomedical applications. COMPUTER METHODS AND PROGRAMS IN BIOMEDICINE 2022; 214:106543. [PMID: 34861616 DOI: 10.1016/j.cmpb.2021.106543] [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: 07/20/2021] [Revised: 11/02/2021] [Accepted: 11/15/2021] [Indexed: 06/13/2023]
Abstract
A numerical procedure for analyzing electromagnetic (EM) fields interactions with biological tissues is presented. The proposed approach aims at drastically reducing the computational burden required by the repeated solution of large scale problems involving the interaction of the human body with EM fields, such as in the study of the time evolution of EM fields, uncertainty quantification, and inverse problems. The proposed volume integral equation (VIE), focused on low frequency applications, is a system of integral equations in terms of current density and scalar potential in the biological tissues excited by EM fields and/or electrodes connected to the human body. The proposed formulation requires the voxelization of the human body and takes advantage of the regularity of such discretization by speeding-up the computational procedure. Moreover, it exploits recent advancements in the solution of VIE by means of iterative preconditioned solvers and ad hoc parametric Model Order Reduction techniques. The efficiency of the proposed tool is demonstrated by applying it to a couple of realistic model problems: the assessment of the peripheral nerve stimulation, performed in terms of evaluation of the induced electric field, due to the gradient coils of a magnetic resonance imaging scanner during a clinical examination and the assessment of the exposure to environmental fields at 50 Hz of live-line workers with uncertain properties of the biological tissues. Thanks to the proposed method, uncertainty quantification analyses and time domain simulations are possible even for large scale problems and they can be performed on standard computers and reasonable computation time. Sample implementation of the method is made publicly available at https://github.com/UniPD-DII-ETCOMP/BioMOR.
Collapse
Affiliation(s)
- Riccardo Torchio
- Department of Industrial Engineering, Università degli Studi di Padova, Padova 35131, Italy.
| | | | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica, Torino 10135, Italy
| | | |
Collapse
|
54
|
Abstract
It is around 20 years since the first commercial 3 T MRI systems became available. The theoretical promise of twice the signal-to-noise ratio of a 1.5 T system together with a greater sensitivity to magnetic susceptibility-related contrast mechanisms, such as the blood oxygen level dependent effect that is the basis for functional MRI, drove the initial market in neuroradiology. However, the limitations of the increased field strength soon became apparent, including the increased radiofrequency power deposition, tissue-dependent changes in relaxation times, increased artifacts, and greater safety concerns. Many of these issues are dependent upon MR physics and workarounds have had to be developed to try and mitigate their effects. This article reviews the underlying principles of the good, the bad and the ugly aspects of 3 T, discusses some of the methods used to improve image quality and explains the remaining challenges and concerns.
Collapse
|
55
|
Seo JH, Mittal R. Computational Modeling of Drug Dissolution in the Human Stomach. Front Physiol 2022; 12:755997. [PMID: 35082685 PMCID: PMC8785969 DOI: 10.3389/fphys.2021.755997] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 10/27/2021] [Indexed: 11/21/2022] Open
Abstract
A computational model of drug dissolution in the human stomach is developed to investigate the interaction between gastric flow and orally administrated drug in the form of a solid tablet. The stomach model is derived from the anatomical imaging data and the motion and dissolution of the drug in the stomach are modeled via fluid-structure interaction combined with mass transport simulations. The effects of gastric motility and the associated fluid dynamics on the dissolution characteristics are investigated. Two different pill densities are considered to study the effects of the gastric flow as well as the gravitational force on the motion of the pill. The average mass transfer coefficient and the spatial distributions of the dissolved drug concentration are analyzed in detail. The results show that the retropulsive jet and recirculating flow in the antrum generated by the antral contraction wave play an important role in the motion of the pill as well as the transport and mixing of the dissolved drug concentration. It is also found that the gastric flow can increase the dissolution mass flux, especially when there is substantial relative motion between the gastric flow and the pill.
Collapse
Affiliation(s)
| | - Rajat Mittal
- Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, United States
| |
Collapse
|
56
|
Akhavanallaf A, Fayad H, Salimi Y, Aly A, Kharita H, Al Naemi H, Zaidi H. An update on computational anthropomorphic anatomical models. Digit Health 2022; 8:20552076221111941. [PMID: 35847523 PMCID: PMC9277432 DOI: 10.1177/20552076221111941] [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: 02/24/2022] [Accepted: 06/19/2022] [Indexed: 11/15/2022] Open
Abstract
The prevalent availability of high-performance computing coupled with validated
computerized simulation platforms as open-source packages have motivated
progress in the development of realistic anthropomorphic computational models of
the human anatomy. The main application of these advanced tools focused on
imaging physics and computational internal/external radiation dosimetry
research. This paper provides an updated review of state-of-the-art developments
and recent advances in the design of sophisticated computational models of the
human anatomy with a particular focus on their use in radiation dosimetry
calculations. The consolidation of flexible and realistic computational models
with biological data and accurate radiation transport modeling tools enables the
capability to produce dosimetric data reflecting actual setup in clinical
setting. These simulation methodologies and results are helpful resources for
the medical physics and medical imaging communities and are expected to impact
the fields of medical imaging and dosimetry calculations profoundly.
Collapse
Affiliation(s)
- Azadeh Akhavanallaf
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva, Switzerland
| | - Hadi Fayad
- Hamad Medical Corporation, Doha, Qatar
- Weill Cornell Medicine, Doha, Qatar
| | - Yazdan Salimi
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva, Switzerland
| | - Antar Aly
- Hamad Medical Corporation, Doha, Qatar
- Weill Cornell Medicine, Doha, Qatar
| | | | - Huda Al Naemi
- Hamad Medical Corporation, Doha, Qatar
- Weill Cornell Medicine, Doha, Qatar
| | - Habib Zaidi
- Division of Nuclear Medicine and Molecular Imaging, Geneva University Hospital, Geneva, Switzerland
- Geneva University Neurocenter, Geneva University, Geneva, Switzerland
- Department of Nuclear Medicine and Molecular Imaging, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
- Department of Nuclear Medicine, University of Southern Denmark, Odense, Denmark
| |
Collapse
|
57
|
Yao A, Yang P, Ma M, Pei Y. Exposure Optimization Trial for Patients With Medical Implants During MRI Exposure: Balance Between the Completeness and Efficiency. Front Public Health 2021; 9:793418. [PMID: 34966716 PMCID: PMC8710503 DOI: 10.3389/fpubh.2021.793418] [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: 10/12/2021] [Accepted: 11/10/2021] [Indexed: 11/13/2022] Open
Abstract
Elongated conductors, such as pacemaker leads, can couple to the MRI radio-frequency (RF) field during MRI scan and cause dangerous tissue heating. By selecting proper RF exposure conditions, the RF-induced power deposition can be suppressed. As the RF-induced power deposition is a complex function of multiple clinical factors, the problem remains how to perform the exposure selection in a comprehensive and efficient way. The purpose of this work is to demonstrate an exposure optimization trail that allows a comprehensive optimization in an efficient and traceable manner. The proposed workflow is demonstrated with a generic 40 cm long cardio pacemaker, major components of the clinical factors are decoupled from the redundant data set using principle component analysis, the optimized exposure condition can not only reduce the in vivo power deposition but also maintain good image quality.
Collapse
Affiliation(s)
- Aiping Yao
- Department of Information Science and Engineering, Lanzhou University, Lanzhou, China
| | - Pengfei Yang
- Centre for Medical Device Evaluation, National Medical Products Administration, Beijing, China
| | - Mingjuan Ma
- Department of Information Science and Engineering, Lanzhou University, Lanzhou, China
| | - Yunfeng Pei
- Department of Information Science and Engineering, Lanzhou University, Lanzhou, China
| |
Collapse
|
58
|
Plumley A, Watkins L, Treder M, Liebig P, Murphy K, Kopanoglu E. Rigid motion-resolved B 1 + prediction using deep learning for real-time parallel-transmission pulse design. Magn Reson Med 2021; 87:2254-2270. [PMID: 34958134 PMCID: PMC7613077 DOI: 10.1002/mrm.29132] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 11/30/2021] [Accepted: 12/03/2021] [Indexed: 11/19/2022]
Abstract
Purpose Tailored parallel-transmit (pTx) pulses produce uniform excitation profiles at 7 T, but are sensitive to head motion. A potential solution is real-time pulse redesign. A deep learning framework is proposed to estimate pTx B1+ distributions following within-slice motion, which can then be used for tailored pTx pulse redesign. Methods Using simulated data, conditional generative adversarial networks were trained to predict B1+ distributions in the head following a displacement. Predictions were made for two virtual body models that were not included in training. Predicted maps were compared with groundtruth (simulated, following motion) B1+ maps. Tailored pTx pulses were designed using B1+ maps at the original position (simulated, no motion) and evaluated using simulated B1+ maps at displaced position (ground-truth maps) to quantify motion-related excitation error. A second pulse was designed using predicted maps (also evaluated on ground-truth maps) to investigate improvement offered by the proposed method. Results Predicted B1+ maps corresponded well with ground-truth maps. Error in predicted maps was lower than motion-related error in 99% and 67% of magnitude and phase evaluations, respectively. Worst-case flip-angle normalized RMS error due to motion (76% of target flip angle) was reduced by 59% when pulses were redesigned using predicted maps. Conclusion We propose a framework for predicting B1+ maps online with deep neural networks. Predicted maps can then be used for real-time tailored pulse redesign, helping to overcome head motion–related error in pTx.
Collapse
Affiliation(s)
- Alix Plumley
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, United Kingdom
| | - Luke Watkins
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, United Kingdom.,School of Physics & Astronomy, Cardiff University Brain Research Imaging Centre (CUBRIC), Cardiff, United Kingdom
| | - Matthias Treder
- School of Computer Science and Informatics, Cardiff University, Cardiff, United Kingdom
| | | | - Kevin Murphy
- School of Physics & Astronomy, Cardiff University Brain Research Imaging Centre (CUBRIC), Cardiff, United Kingdom
| | - Emre Kopanoglu
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, United Kingdom
| |
Collapse
|
59
|
Ahn J, Hong SE, Kim H, Song K, Choi HD, Ahn S. Improved Calculation Method of Coupling Factors for Low-Frequency Wireless Power Transfer Systems. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2021; 19:44. [PMID: 35010303 PMCID: PMC8751195 DOI: 10.3390/ijerph19010044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/27/2021] [Revised: 12/14/2021] [Accepted: 12/15/2021] [Indexed: 06/14/2023]
Abstract
The concept of a coupling factor was introduced in International Electrotechnical Commission (IEC) 62311 and 62233 to provide a product safety assessment that considers the localized exposure when an electromagnetic field (EMF) source is close to the human body. To calculate the coupling factors between the human body and EMF source, a numerical calculation should be carried out to calculate the internal quantities of the human body models. However, at frequencies below 10 MHz, the computed current density or internal electric field has computational artifacts from segmentation or discretization errors. Specifically, coupling factors are calculated based on the maximum values, which may include computational artifacts due to abnormal peaks. In this study, we propose an improved calculation method to remove computational artifacts by applying the 99.99th percentile in calculating the coupling factors without underestimation. The performance of the proposed method is verified through a comparison based on various human body models with wireless power transfer (WPT) systems and compliance with the reference levels and basic restrictions. The results indicate that the proposed method can provide uniform coupling factors by reducing the computational errors by up to 65.3% compared to a conventional method.
Collapse
Affiliation(s)
- Jangyong Ahn
- The CCS Graduate School of Green Transportation, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34051, Korea; (J.A.); (H.K.); (K.S.)
| | - Seon-Eui Hong
- Radio and Satellite Research Division, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea; (S.-E.H.); (H.-D.C.)
| | - Haerim Kim
- The CCS Graduate School of Green Transportation, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34051, Korea; (J.A.); (H.K.); (K.S.)
| | - Kyunghwan Song
- The CCS Graduate School of Green Transportation, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34051, Korea; (J.A.); (H.K.); (K.S.)
| | - Hyung-Do Choi
- Radio and Satellite Research Division, Electronics and Telecommunications Research Institute (ETRI), Daejeon 34129, Korea; (S.-E.H.); (H.-D.C.)
| | - Seungyoung Ahn
- The CCS Graduate School of Green Transportation, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34051, Korea; (J.A.); (H.K.); (K.S.)
| |
Collapse
|
60
|
McCullough JWS, Coveney PV. High fidelity blood flow in a patient-specific arteriovenous fistula. Sci Rep 2021; 11:22301. [PMID: 34785678 PMCID: PMC8595446 DOI: 10.1038/s41598-021-01435-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 10/05/2021] [Indexed: 12/24/2022] Open
Abstract
An arteriovenous fistula, created by artificially connecting segments of a patient’s vasculature, is the preferred way to gain access to the bloodstream for kidney dialysis. The increasing power and availability of supercomputing infrastructure means that it is becoming more realistic to use simulations to help identify the best type and location of a fistula for a specific patient. We describe a 3D fistula model that uses the lattice Boltzmann method to simultaneously resolve blood flow in patient-specific arteries and veins. The simulations conducted here, comprising vasculatures of the whole forearm, demonstrate qualified validation against clinical data. Ongoing research to further encompass complex biophysics on realistic time scales will permit the use of human-scale physiological models for basic and clinical medicine.
Collapse
Affiliation(s)
- J W S McCullough
- Centre for Computational Science, Department of Chemistry, University College London, London, UK
| | - P V Coveney
- Centre for Computational Science, Department of Chemistry, University College London, London, UK. .,Informatics Institute, University of Amsterdam, Amsterdam, The Netherlands.
| |
Collapse
|
61
|
Wang Y, Guo R, Hu W, Jiang J, Kainz W, Chen J. MR Conditionality of Abandoned Leads from Active Implantable Medical Devices at 1.5T. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2021; 2021:7412-7415. [PMID: 34892810 DOI: 10.1109/embc46164.2021.9630892] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
During Magnetic Resonance (MR) scans, abandoned leads from active implantable medical devices (AIMDs) can experience excessive heating near the lead-tip, depending on the types of termination applied to the proximal end. The influence of different proximal treatments, i.e., (i) freely exposed in the tissue, (ii) capped with metallic material, and (iii) capped with plastic material on the RF-induced heating are studied. Abandoned leads from a sacral neuromodulation (SNM) system were investigated in this study. The device models, i.e., the transfer functions, for different proximal treatments were developed. These models are then used to assess the in-vivo lead-tip heating inside four virtual human models (FATS, Duke, Ella, and Billie). The RF-induced heating from these abandoned leads with different proximal end treatments are compared with the lead-tip heating of the original AIMD system. The maximum lead-tip heating for abandoned leads using metal cap at the proximal end is lower than that from the original intact AIMD system. Abandoned leads with plastic cap treatment at the proximal end will lead to an average in-vivo temperature that is 3.5 times higher than that from the original intact AIMD system. Therefore, from this study and in terms of the RF-induced heating, the abandoned leads with metallic cap treatment at the proximal end can maintain the MR conditionality of the original AIMD system.Clinical Relevance- The different treatments of proximal end of the abandoned leads from AIMD are studied to ensure that MR Conditional AIMD leads remain MR Conditional when the leads are abandoned in the patients.
Collapse
|
62
|
Priovoulos N, Roos T, Ipek Ö, Meliado EF, Nkrumah RO, Klomp DWJ, van der Zwaag W. A local multi-transmit coil combined with a high-density receive array for cerebellar fMRI at 7 T. NMR IN BIOMEDICINE 2021; 34:e4586. [PMID: 34231292 PMCID: PMC8519055 DOI: 10.1002/nbm.4586] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 06/09/2021] [Accepted: 06/22/2021] [Indexed: 06/13/2023]
Abstract
The human cerebellum is involved in a wide array of functions, ranging from motor control to cognitive control, and as such is of great neuroscientific interest. However, its function is underexplored in vivo, due to its small size, its dense structure and its placement at the bottom of the brain, where transmit and receive fields are suboptimal. In this study, we combined two dense coil arrays of 16 small surface receive elements each with a transmit array of three antenna elements to improve BOLD sensitivity in the human cerebellum at 7 T. Our results showed improved B1+ and SNR close to the surface as well as g-factor gains compared with a commercial coil designed for whole-head imaging. This resulted in improved signal stability and large gains in the spatial extent of the activation close to the surface (<3.5 cm), while good performance was retained deeper in the cerebellum. Modulating the phase of the transmit elements of the head coil to constructively interfere in the cerebellum improved the B1+ , resulting in a temporal SNR gain. Overall, our results show that a dedicated transmit array along with the SNR gains of surface coil arrays can improve cerebellar imaging, at the cost of a decreased field of view and increased signal inhomogeneity.
Collapse
Affiliation(s)
- Nikos Priovoulos
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
| | - Thomas Roos
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
| | - Özlem Ipek
- Department of Biomedical Engineering, School of Biomedical Engineering & Imaging SciencesKing's College LondonLondonUK
| | - Ettore F. Meliado
- Image Sciences InstituteUniversity Medical Center UtrechtUtrechtNetherlands
| | - Richard O. Nkrumah
- Department of Biomedical Engineering, School of Biomedical Engineering & Imaging SciencesKing's College LondonLondonUK
| | - Dennis W. J. Klomp
- Image Sciences InstituteUniversity Medical Center UtrechtUtrechtNetherlands
| | - Wietske van der Zwaag
- Spinoza Center for NeuroimagingRoyal Netherlands Academy of Arts and Sciences (KNAW)AmsterdamThe Netherlands
| |
Collapse
|
63
|
Irastorza RM, Bovaira M, García-Vitoria C, Muñoz V, Berjano E. Effect of the relative position of electrode and stellate ganglion during thermal radiofrequency ablation: a simulation study. Int J Hyperthermia 2021; 38:1502-1511. [PMID: 34674597 DOI: 10.1080/02656736.2021.1974580] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022] Open
Abstract
PURPOSE Stellate ganglion (SG) block by thermal radiofrequency ablation (RFA) is frequently conducted as a therapeutic intervention for sympathetic-maintained and neuropathic pain syndromes. RFA's partial lack of effectiveness could be partly due to the ablation zone (AZ) not completely covering the SG section and therefore preventing the 'cutting' of the afferent pathways. Our objective was to build a theoretical model to conduct computer simulations to assess the effect of the electrode position relative to the SG. METHODS A three-dimensional model was built including the SG and adjacent tissues (vertebrae C7-T1-T2, trachea, carotid artery and vertebral artery). RFA (90-s, 80 °C) was simulated considering a 22 G-5 mm electrode. The AZ was computed using the 50 °C isotherm. RESULTS An electrode displacement of 2 mm in any direction from the optimal position (centered on the SG) meant that the AZ did not fully cover the SG section. Likewise, SG size considerably affected the RFA effectiveness since the AZ fully covered the section of small but not large SGs. CONCLUSIONS The findings suggest that the currently used SG RFA settings (i.e., 22 G-5 mm electrode, 90-s, 80 °C) may not be appropriate due to their inability to achieve an AZ that fully covers the SG cross section under certain circumstances, such as a large SG and non-optimal positioning of the RF electrode with respect to the SG center.
Collapse
Affiliation(s)
- Ramiro M Irastorza
- Instituto de Física de Líquidos y Sistemas Biológicos (CONICET), La Plata, Argentina.,Instituto de Ingeniería y Agronomía, Universidad Nacional Arturo Jauretche, Florencio Varela, Argentina
| | - Maite Bovaira
- Department of Anesthesiology, Critical Care and Pain Management, Hospital Intermutual de Levante, Valencia, Spain
| | - Carles García-Vitoria
- Department of Anesthesiology, Critical Care and Pain Management, Hospital Intermutual de Levante, Valencia, Spain
| | | | - Enrique Berjano
- BioMIT, Department of Electronic Engineering, Universitat Politècnica de València, Valencia, Spain
| |
Collapse
|
64
|
Audenaert EA, Duquesne K, De Roeck J, Mutsvangwa T, Borotikar B, Khanduja V, Claes P. Ischiofemoral impingement: the evolutionary cost of pelvic obstetric adaptation. J Hip Preserv Surg 2021; 7:677-687. [PMID: 34548927 PMCID: PMC8448428 DOI: 10.1093/jhps/hnab004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2020] [Revised: 01/06/2021] [Accepted: 01/13/2021] [Indexed: 12/29/2022] Open
Abstract
The risk for ischiofemoral impingement has been mainly related to a reduced ischiofemoral distance and morphological variance of the femur. From an evolutionary perspective, however, there are strong arguments that the condition may also be related to sexual dimorphism of the pelvis. We, therefore, investigated the impact of gender-specific differences in anatomy of the ischiofemoral space on the ischiofemoral clearance, during static and dynamic conditions. A random sampling Monte-Carlo experiment was performed to investigate ischiofemoral clearance during stance and gait in a large (n = 40 000) virtual study population, while using gender-specific kinematics. Subsequently, a validated gender-specific geometric morphometric analysis of the hip was performed and correlations between overall hip morphology (statistical shape analysis) and standard discrete measures (conventional metric approach) with the ischiofemoral distance were evaluated. The available ischiofemoral space is indeed highly sexually dimorphic and related primarily to differences in the pelvic anatomy. The mean ischiofemoral distance was 22.2 ± 4.3 mm in the females and 29.1 ± 4.1 mm in the males and this difference was statistically significant (P < 0.001). Additionally, the ischiofemoral distance was observed to be a dynamic measure, and smallest during femoral extension, and this in turn explains the clinical sign of pain in extension during long stride walking. In conclusion, the presence of a reduced ischiofemroal distance and related risk to develop a clinical syndrome of ischiofemoral impingement is strongly dominated by evolutionary effects in sexual dimorphism of the pelvis. This should be considered when female patients present with posterior thigh/buttock pain, particularly if worsened by extension. Controlled laboratory study.
Collapse
Affiliation(s)
- E A Audenaert
- Department of Orthopedic Surgery and Traumatology, Ghent University Hospital, Corneel Heymanslaan 10, Ghent 9000, Belgium.,Department of Trauma and Orthopedics, Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge CB2 0QQ, UK.,Department of Electromechanics, Op3Mech Research Group, University of Antwerp, Groenenborgerlaan 171, Antwerp 2020, Belgium.,Department of Human Structure and Repair, Ghent University, Corneel Heymanslaan 10, Ghent 9000, Belgium
| | - K Duquesne
- Department of Human Structure and Repair, Ghent University, Corneel Heymanslaan 10, Ghent 9000, Belgium
| | - J De Roeck
- Department of Human Structure and Repair, Ghent University, Corneel Heymanslaan 10, Ghent 9000, Belgium
| | - T Mutsvangwa
- Division of Biomedical Engineering, University of Cape Town, Anzio Rd, Observatory, Cape Town 7925, South Africa
| | - B Borotikar
- Symbiosis Center for Medical Image Analysis, Symbiosis International University, Lavale, Mulshi District, Pune 412115, India.,Laboratory of Medical Information Processing (LaTIM), UMR 1101, INSERM, Avenue Foch 12, 29200 Brest, France
| | - V Khanduja
- Department of Trauma and Orthopedics, Addenbrooke's Hospital, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge CB2 0QQ, UK
| | - P Claes
- Department of Human Genetics, KU Leuven, Herestraat 49, 3000 Leuven, Belgium.,Medical Imaging Research Center, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium.,Department of Electrical Engineering, ESAT/PSI, KU Leuven, Herestraat 49, 3000 Leuven, Belgium.,Murdoch Children's Research Institute, Melbourne, Flemington Road, Parkville Victoria 3052, Australia
| |
Collapse
|
65
|
Zanoli M, Trefná HD. Suitability of eigenvalue beam-forming for discrete multi-frequency hyperthermia treatment planning. Med Phys 2021; 48:7410-7426. [PMID: 34529281 DOI: 10.1002/mp.15220] [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: 12/24/2020] [Revised: 08/06/2021] [Accepted: 08/06/2021] [Indexed: 11/11/2022] Open
Abstract
PURPOSE Thermal dose delivery in microwave hyperthermia for cancer treatment is expected to benefit from the introduction of ultra-wideband (UWB)-phased array applicators. A full exploitation of the combination of different frequencies to improve the deposition pattern is, however, a nontrivial problem. It is unclear whether the cost functions used for hyperthermia treatment planning (HTP) optimization in the single-frequency setting can be meaningfully extended to the UWB case. METHOD We discuss the ability of the eigenvalue (EV) and a novel implementation of iterative-EV (i-EV) beam-forming methods to fully exploit the available frequency spectrum when a discrete set of simultaneous operating frequencies is available for treatment. We show that the quadratic power deposition ratio solved by the methods can be maximized by only one frequency in the set, therefore rendering EV inadequate for UWB treatment planning. We further investigate whether this represents a limitation in two realistic test cases, comparing the thermal distributions resulting from EV and i-EV to those obtained by optimizing for other nonlinear cost functions that allow for multi-frequency. RESULTS The classical EV-based single-frequency HTP yields systematically lower target SAR deposition and temperature values than nonlinear HTP. In a larynx target, the proposed single-frequency i-EV scheme is able to compensate for this and reach temperatures comparable to those given by global nonlinear optimization. In a meninges target, the multi-frequency setting outperforms the single-frequency one, achieving better target coverage and 0 . 5 ∘ C higher T 90 in the tumor than single-frequency-based HTP. CONCLUSIONS Classical EV performs poorly in terms of resulting target temperatures. The proposed single-frequency i-EV scheme can be a viable option depending on the patient and tumor to be treated, as long as the proper operating frequency can be selected across a UWB range. Multi-frequency HTP can bring a considerable benefit in regions typically difficult to treat such as the brain.
Collapse
Affiliation(s)
- Massimiliano Zanoli
- Department of Electrical Engineering, Chalmers University of Technology, Göteborg, Sweden
| | - Hana Dobšíček Trefná
- Department of Electrical Engineering, Chalmers University of Technology, Göteborg, Sweden
| |
Collapse
|
66
|
Yao A, Murbach M, Goren T, Zastrow E, Kainz W, Kuster N. Induced radiofrequency fields in patients undergoing MR examinations: insights for risk assessment. Phys Med Biol 2021; 66. [PMID: 34433143 DOI: 10.1088/1361-6560/ac212d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Accepted: 08/25/2021] [Indexed: 11/11/2022]
Abstract
Purpose. To characterize and quantify the induced radiofrequency (RF) electric (E)-fields andB1+rmsfields in patients undergoing magnetic resonance (MR) examinations; to provide guidance on aspects of RF heating risks for patients with and without implants; and to discuss some strengths and limitations of safety assessments in current ISO, IEC, and ASTM standards to determine the RF heating risks for patients with and without implants.Methods. InducedE-fields andB1+rmsfields during 1.5 T and 3 T MR examinations were numerically estimated for high-resolution patient models of the Virtual Population exposed to ten two-port birdcage RF coils from head to feet imaging landmarks over the full polarization space, as well as in surrogate ASTM phantoms.Results. Worst-caseB1+rmsexposure greater than 3.5μT (1.5 T) and 2μT (3 T) must be considered for all MR examinations at the Normal Operating Mode limit. Representative inducedE-field and specific absorption rate distributions under different clinical scenarios allow quick estimation of clinical factors of high and reduced exposure.B1shimming can cause +6 dB enhancements toE-fields along implant trajectories. The distribution and magnitude of inducedE-fields in the ASTM phantom differ from clinical exposures and are not always conservative for typical implant locations.Conclusions.Field distributions in patient models are condensed, visualized for quick estimation of risks, and compared to those induced in the ASTM phantom. InducedE-fields in patient models can significantly exceed those in the surrogate ASTM phantom in some cases. In the recent 19ε2revision of the ASTM F2182 standard, the major shortcomings of previous versions have been addressed by requiring that the relationship between ASTM test conditions andin vivotangentialE-fields be established, e.g. numerically. With this requirement, the principal methods defined in the ASTM standard for passive implants are reconciled with those of the ISO 10974 standard for active implantable medical devices.
Collapse
Affiliation(s)
- Aiping Yao
- IT'IS Foundation, 8004 Zurich, Switzerland.,Swiss Federal Institute of Technology (ETH) Zurich, 8092 Zurich, Switzerland
| | | | | | | | - Wolfgang Kainz
- US Food and Drug Administration (FDA), Center for Devices and Radiological Health (CDRH), Silver Spring, MD 20993, United States of America
| | - Niels Kuster
- IT'IS Foundation, 8004 Zurich, Switzerland.,Swiss Federal Institute of Technology (ETH) Zurich, 8092 Zurich, Switzerland
| |
Collapse
|
67
|
Evaluation of the whole auditory pathway using high-resolution and functional MRI at 7T parallel-transmit. PLoS One 2021; 16:e0254378. [PMID: 34492032 PMCID: PMC8423236 DOI: 10.1371/journal.pone.0254378] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2020] [Accepted: 06/24/2021] [Indexed: 11/29/2022] Open
Abstract
Purpose The aim of the present study is to show a MR procedure for the evaluation of simultaneous left and right auditory functions with functional MRI, and high-resolution acquisition of anatomical auditory pathway using parallel-transmit (pTx) methods at 7T. Methods The time-efficient MR acquisition included two steps: RF weights were optimized for the regions-of-interest and high-resolution MR images of the inner-ear were acquired for the first 30 min (400 μm-iso resolution) followed by functional MRI acquisitions along the whole auditory pathway during the next 20 minutes. Data was processed with a linear cross-correlation analysis to define frequency preferences for each voxel in the auditory relays. Results Tonotopic maps revealed ordered bilateral frequency gradients in the auditory relays whereas at the level of the cochlear nuclei and superior olivary complexes the frequency gradients were less evident. A 21% increase in transmit-field efficiency was achieved over the left/right inner-ear regions and thus its main structures were clearly discernible using the pTx methods, compared to a single transmit RF coil. Conclusion Using 7T pTx allows a fast (less than 60 min in total) and qualitative evaluation of the simultaneous left and right auditory response along the entire auditory pathway, together with high-resolution anatomical images of the inner-ear. This could be further used for patient examination at 7T.
Collapse
|
68
|
van Leeuwen CC, Steensma BR, Klomp DWJ, van den Berg CAT, Raaijmakers AJE. The Coax Dipole: A fully flexible coaxial cable dipole antenna with flattened current distribution for body imaging at 7 Tesla. Magn Reson Med 2021; 87:528-540. [PMID: 34411327 PMCID: PMC9292881 DOI: 10.1002/mrm.28983] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 07/14/2021] [Accepted: 08/04/2021] [Indexed: 01/26/2023]
Abstract
Purpose The coax dipole antenna, a flexible antenna for body imaging at 7T is presented. Similar to the high impedance coil, this coaxial cable antenna is fed on the central conductor and through gaps in the shield, the current passes to the outside of the antenna to generate B1 field. This could achieve more favorable current distributions and better adaptation to the body curvature. Methods Finite difference time domain (FDTD) simulations are performed to optimize the positions of the gaps in the shield for a flat current profile. Lumped inductors are added to each end to reduce losses. The performance of a single antenna is compared to a fractionated dipole using B1 maps and MR thermometry. Finally, an array of eight coax dipoles is evaluated in simulations and used for in‐vivo scanning. Results An optimal configuration is found with gaps located at 10 cm from the center and inductor values of 28 nH. In comparison to the fractionated dipole antenna, in single antenna phantom measurements the coax dipole achieves similar B1 amplitude with 18% lower peak temperature. In simulations, the eight‐channel array of coax dipoles improved B1 homogeneity by 18%, along with small improvements in transmit efficiency and specific absorption rate (SAR). MRI measurements on three volunteers show more consistent performance for the coax dipoles. Conclusion The coax dipole is a novel antenna design with a flattened current distribution resulting in beneficial properties. Also, the flexible design of the coax dipoles allows better adaptation to the body curvature and can potentially be used for a wide range of imaging targets.
Collapse
Affiliation(s)
- Carel C van Leeuwen
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Bart R Steensma
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | - Dennis W J Klomp
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
| | | | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.,Biomedical Engineering Department, Eindhoven University of Technology, Eindhoven, The Netherlands
| |
Collapse
|
69
|
Wang Y, Guo R, Hu W, Zheng J, Wang Q, Jiang J, Kurpad KKN, Kaula N, Long S, Chen J, Kainz W. Magnetic resonance conditionality of abandoned leads from active implantable medical devices at 1.5 T. Magn Reson Med 2021; 87:394-408. [PMID: 34378816 DOI: 10.1002/mrm.28967] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 06/26/2021] [Accepted: 07/26/2021] [Indexed: 11/07/2022]
Abstract
PURPOSE During MR scans, abandoned leads from active implantable medical devices (AIMDs) can experience excessive heating at the lead tip, depending on the type of termination applied to the proximal contacts (proximal end treatment). The influence of different proximal end treatments (ie, [1] freely exposed in the tissue, [2] terminated with metal in contact with the tissue, or [3] capped with plastic, and thereby fully insulated, on the RF-induced lead-tip heating) are studied. A technique to ensure that MR Conditional AIMD leads remain MR Conditional even when abandoned is recommended. METHODS Abandoned leads from three MR Conditional AIMDs ([1] a sacral neuromodulation system, [2] a cardiac rhythm management pacemaker system, and [3] a deep brain stimulator system) were investigated in this study. The computational lead models (ie, the transfer functions) for different proximal end treatments were measured and used to assess the in vivo lead-tip heating for four virtual human models (FATS, Duke, Ella, and Billie) and compared with the lead-tip heating of the complete MR Conditional AIMD system. RESULT The average and maximum lead-tip heating for abandoned leads proximally capped with metal is always lower than that from the complete AIMD system. Abandoned leads proximally insulated could lead to an average in vivo temperature rise up to 3.5 times higher than that from the complete AIMD system. CONCLUSION For the three investigated AIMDs under 1.5T MR scanning, our results indicate that RF-induced lead-tip heating of abandoned leads strongly depends on the proximal lead termination. A metallic cap applied to the proximal termination of the tested leads could significantly reduce the RF-induced lead-tip heating.
Collapse
Affiliation(s)
- Yu Wang
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Ran Guo
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Wei Hu
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Jianfeng Zheng
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Qingyan Wang
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Jay Jiang
- Axonics Modulation Technologies, Irvine, California, USA
| | | | | | - Stuart Long
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Ji Chen
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Wolfgang Kainz
- Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, Maryland, USA
| |
Collapse
|
70
|
Godinho DM, Felício JM, Castela T, Silva NA, Orvalho MDL, Fernandes CA, Conceição RC. Development of MRI-based axillary numerical models and estimation of axillary lymph node dielectric properties for microwave imaging. Med Phys 2021; 48:5974-5990. [PMID: 34338335 DOI: 10.1002/mp.15143] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2021] [Revised: 07/20/2021] [Accepted: 07/22/2021] [Indexed: 11/11/2022] Open
Abstract
PURPOSE Microwave imaging (MWI) has been studied as a complementary imaging modality to improve sensitivity and specificity of diagnosis of axillary lymph nodes (ALNs), which can be metastasized by breast cancer. The feasibility of such a system is based on the dielectric contrast between healthy and metastasized ALNs. However, reliable information such as anatomically realistic numerical models and matching dielectric properties of the axillary region and ALNs, which are crucial to develop MWI systems, are still limited in the literature. The purpose of this work is to develop a methodology to infer dielectric properties of structures from magnetic resonance imaging (MRI), in particular, ALNs. We further use this methodology, which is tailored for structures farther away from MR coils, to create MRI-based numerical models of the axillary region and share them with the scientific community, through an open-access repository. METHODS We use a dataset of breast MRI scans of 40 patients, 15 of them with metastasized ALNs. We apply image processing techniques to minimize the artifacts in MR images and segment the tissues of interest. The background, lung cavity, and skin are segmented using thresholding techniques and the remaining tissues are segmented using a K-means clustering algorithm. The ALNs are segmented combining the clustering results of two MRI sequences. The performance of this methodology was evaluated using qualitative criteria. We then apply a piecewise linear interpolation between voxel signal intensities and known dielectric properties, which allow us to create dielectric property maps within an MRI and consequently infer ALN properties. Finally, we compare healthy and metastasized ALN dielectric properties within and between patients, and we create an open-access repository of numerical axillary region numerical models which can be used for electromagnetic simulations. RESULTS The proposed methodology allowed creating anatomically realistic models of the axillary region, segmenting 80 ALNs and analyzing the corresponding dielectric properties. The estimated relative permittivity of those ALNs ranged from 16.6 to 49.3 at 5 GHz. We observe there is a high variability of dielectric properties of ALNs, which can be mainly related to the ALN size and, consequently, its composition. We verified an average dielectric contrast of 29% between healthy and metastasized ALNs. Our repository comprises 10 numerical models of the axillary region, from five patients, with variable number of metastasized ALNs and body mass index. CONCLUSIONS The observed contrast between healthy and metastasized ALNs is a good indicator for the feasibility of a MWI system aiming to diagnose ALNs. This paper presents new contributions regarding anatomical modeling and dielectric properties' characterization, in particular for axillary region applications.
Collapse
Affiliation(s)
- Daniela M Godinho
- Instituto de Biofísica e Engenharia Biomédica, Faculdade de Ciências da Universidade de Lisboa, Lisbon, Portugal
| | - João M Felício
- Centro de Investigação Naval (CINAV), Escola Naval, Almada, Portugal.,Instituto de Telecomunicações, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
| | - Tiago Castela
- Departamento de Radiologia, Hospital da Luz Lisboa, Luz Saúde, Lisbon, Portugal
| | - Nuno A Silva
- Hospital da Luz Learning Health, Luz Saúde, Lisbon, Portugal
| | | | - Carlos A Fernandes
- Instituto de Telecomunicações, Instituto Superior Técnico, Universidade de Lisboa, Lisbon, Portugal
| | - Raquel C Conceição
- Instituto de Biofísica e Engenharia Biomédica, Faculdade de Ciências da Universidade de Lisboa, Lisbon, Portugal
| |
Collapse
|
71
|
Boehm C, Sollmann N, Meineke J, Ruschke S, Dieckmeyer M, Weiss K, Zimmer C, Makowski MR, Baum T, Karampinos DC. Preconditioned water-fat total field inversion: Application to spine quantitative susceptibility mapping. Magn Reson Med 2021; 87:417-430. [PMID: 34255370 DOI: 10.1002/mrm.28903] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 05/14/2021] [Accepted: 06/07/2021] [Indexed: 02/05/2023]
Abstract
PURPOSE To (a) develop a preconditioned water-fat total field inversion (wfTFI) algorithm that directly estimates the susceptibility map from complex multi-echo gradient echo data for water-fat regions and to (b) evaluate the performance of the proposed wfTFI quantitative susceptibility mapping (QSM) method in comparison with a local field inversion (LFI) method and a linear total field inversion (TFI) method in the spine. METHODS Numerical simulations and in vivo spine multi-echo gradient echo measurements were performed to compare wfTFI to an algorithm based on disjoint background field removal (BFR) and LFI and to a formerly proposed TFI algorithm. The data from 1 healthy volunteer and 10 patients with metastatic bone disease were included in the analysis. Clinical routine computed tomography (CT) images were used as a reference standard to distinguish osteoblastic from osteolytic changes. The ability of the QSM methods to distinguish osteoblastic from osteolytic changes was evaluated. RESULTS The proposed wfTFI method was able to decrease the normalized root mean square error compared to the LFI and TFI methods in the simulation. The in vivo wfTFI susceptibility maps showed reduced BFR artifacts, noise amplification, and streaking artifacts compared to the LFI and TFI maps. wfTFI provided a significantly higher diagnostic confidence in differentiating osteolytic and osteoblastic lesions in the spine compared to the LFI method (p = .012). CONCLUSION The proposed wfTFI method can minimize BFR artifacts, noise amplification, and streaking artifacts in water-fat regions and can thus better differentiate between osteoblastic and osteolytic changes in patients with metastatic disease compared to LFI and the original TFI method.
Collapse
Affiliation(s)
- Christof Boehm
- Department of Diagnostic and Interventional Radiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Nico Sollmann
- Department of Diagnostic and Interventional Neuroradiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.,TUM-Neuroimaging Center, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.,Department of Diagnostic and Interventional Radiology, University Hospital Ulm, Ulm, Germany
| | | | - Stefan Ruschke
- Department of Diagnostic and Interventional Radiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Michael Dieckmeyer
- Department of Diagnostic and Interventional Neuroradiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | | | - Claus Zimmer
- Department of Diagnostic and Interventional Neuroradiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany.,TUM-Neuroimaging Center, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Marcus R Makowski
- Department of Diagnostic and Interventional Radiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Thomas Baum
- Department of Diagnostic and Interventional Neuroradiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| | - Dimitrios C Karampinos
- Department of Diagnostic and Interventional Radiology, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, Munich, Germany
| |
Collapse
|
72
|
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.
Collapse
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
| |
Collapse
|
73
|
Rubia-Rodríguez I, Zilberti L, Arduino A, Bottauscio O, Chiampi M, Ortega D. In silico assessment of collateral eddy current heating in biocompatible implants subjected to magnetic hyperthermia treatments. Int J Hyperthermia 2021; 38:846-861. [PMID: 34074196 DOI: 10.1080/02656736.2021.1909758] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Purpose: Bearing partially or fully metallic passive implants represents an exclusion criterion for patients undergoing a magnetic hyperthermia procedure, but there are no specific studies backing this restrictive decision. This work assesses how the secondary magnetic field generated at the surface of two common types of prostheses affects the safety and efficiency of magnetic hyperthermia treatments of localized tumors. The paper also proposes the combination of a multi-criteria decision analysis and a graphical representation of calculated data as an initial screening during the preclinical risk assessment for each patient.Materials and methods: Heating of a hip joint and a dental implant during the treatment of prostate, colorectal and head and neck tumors have been assessed considering different external field conditions and exposure times. The Maxwell equations including the secondary field produced by metallic prostheses have been solved numerically in a discretized computable human model. The heat exchange problem has been solved through a modified version of the Pennes' bioheat equation assuming a temperature dependency of blood perfusion and metabolic heat, i.e. thermorregulation. The degree of risk has been assessed using a risk index with parameters coming from custom graphs plotting the specific absorption rate (SAR) vs temperature increase, and coefficients derived from a multi-criteria decision analysis performed following the MACBETH approach.Results: The comparison of two common biomaterials for passive implants - Ti6Al4V and CoCrMo - shows that both specific absorption rate (SAR) and local temperature increase are found to be higher for the hip prosthesis made by Ti6Al4V despite its lower electrical and thermal conductivity. By tracking the time evolution of temperature upon field application, it has been established that there is a 30 s delay between the time point for which the thermal equilibrium is reached at prostheses and tissues. Likewise, damage may appear in those tissues adjacent to the prostheses at initial stages of treatment, since recommended thermal thresholds are soon surpassed for higher field intensities. However, it has also been found that under some operational conditions the typical safety rule of staying below or attain a maximum temperature increase or SAR value is met.Conclusion: The current exclusion criterion for implant-bearing patients in magnetic hyperthermia should be revised, since it may be too restrictive for a range of the typical field conditions used. Systematic in silico treatment planning using the proposed methodology after a well-focused diagnostic procedure can aid the clinical staff to find the appropriate limits for a safe treatment window.
Collapse
Affiliation(s)
| | - Luca Zilberti
- Istituto Nazionale di Ricerca Metrologica (INRIM), Turin, Italy
| | | | | | - Mario Chiampi
- Istituto Nazionale di Ricerca Metrologica (INRIM), Turin, Italy
| | - Daniel Ortega
- IMDEA Nanoscience, Madrid, Spain.,Institute of Research and Innovation in Biomedical Sciences of the Province of Cádiz (INiBICA), University of Cádiz, Cádiz, Spain.,Condensed Matter Physics department, University of Cádiz, Cádiz, Spain
| |
Collapse
|
74
|
Poni R, Neufeld E, Capstick M, Bodis S, Samaras T, Kuster N. Feasibility of Temperature Control by Electrical Impedance Tomography in Hyperthermia. Cancers (Basel) 2021; 13:3297. [PMID: 34209300 PMCID: PMC8268554 DOI: 10.3390/cancers13133297] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2021] [Revised: 06/23/2021] [Accepted: 06/25/2021] [Indexed: 11/17/2022] Open
Abstract
We present a simulation study investigating the feasibility of electrical impedance tomography (EIT) as a low cost, noninvasive technique for hyperthermia (HT) treatment monitoring and adaptation. Temperature rise in tissues leads to perfusion and tissue conductivity changes that can be reconstructed in 3D by EIT to noninvasively map temperature and perfusion. In this study, we developed reconstruction methods and investigated the achievable accuracy of EIT by simulating HT treatmentlike scenarios, using detailed anatomical models with heterogeneous conductivity distributions. The impact of the size and location of the heated region, the voltage measurement signal-to-noise ratio, and the reference model personalization and accuracy were studied. Results showed that by introducing an iterative reconstruction approach, combined with adaptive prior regions and tissue-dependent penalties, planning-based reference models, measurement-based reweighting, and physics-based constraints, it is possible to map conductivity-changes throughout the heated domain, with an accuracy of around 5% and cm-scale spatial resolution. An initial exploration of the use of multifrequency EIT to separate temperature and perfusion effects yielded promising results, indicating that temperature reconstruction accuracy can be in the order of 1 ∘C. Our results suggest that EIT can provide valuable real-time HT monitoring capabilities. Experimental confirmation in real-world conditions is the next step.
Collapse
Affiliation(s)
- Redi Poni
- Department of Information Technology and Electrical Engineering, Swiss Federal Institute of Technology (ETH), 8092 Zurich, Switzerland; (R.P.); (N.K.)
- Foundation for Research on Information Technologies in Society (IT’IS), 8004 Zurich, Switzerland; (M.C.); (S.B.)
| | - Esra Neufeld
- Department of Information Technology and Electrical Engineering, Swiss Federal Institute of Technology (ETH), 8092 Zurich, Switzerland; (R.P.); (N.K.)
- Foundation for Research on Information Technologies in Society (IT’IS), 8004 Zurich, Switzerland; (M.C.); (S.B.)
| | - Myles Capstick
- Foundation for Research on Information Technologies in Society (IT’IS), 8004 Zurich, Switzerland; (M.C.); (S.B.)
| | - Stephan Bodis
- Foundation for Research on Information Technologies in Society (IT’IS), 8004 Zurich, Switzerland; (M.C.); (S.B.)
- Center of Radiation Oncology KSA-KSB, Kantonsspital Aarau, 5001 Aarau, Switzerland
| | - Theodoros Samaras
- Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece;
| | - Niels Kuster
- Department of Information Technology and Electrical Engineering, Swiss Federal Institute of Technology (ETH), 8092 Zurich, Switzerland; (R.P.); (N.K.)
- Foundation for Research on Information Technologies in Society (IT’IS), 8004 Zurich, Switzerland; (M.C.); (S.B.)
| |
Collapse
|
75
|
Bellizzi GG, Sumser K, VilasBoas-Ribeiro I, Curto S, Drizdal T, van Rhoon GC, Franckena M, Paulides MM. Standardization of patient modeling in hyperthermia simulation studies: introducing the Erasmus Virtual Patient Repository. Int J Hyperthermia 2021; 37:608-616. [PMID: 32515240 DOI: 10.1080/02656736.2020.1772996] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Purpose: Thermal dose-effect relations have demonstrated that clinical effectiveness of hyperthermia would benefit from more controlled heating of the tumor. Hyperthermia treatment planning (HTP) is a potent tool to study strategies enabling target conformal heating, but its accuracy is affected by patient modeling approximations. Homogeneous phantoms models are being used that do not match the body shape of patients in treatment position and often have unrealistic target volumes. As a consequence, simulation accuracy is affected, and performance comparisons are difficult. The aim of this study is to provide the first step toward standardization of HTP simulation studies in terms of patient modeling by introducing the Erasmus Virtual Patient Repository (EVPR): a virtual patient model database.Methods: Four patients with a tumor in the head and neck or the pelvis region were selected, and corresponding models were created using a clinical segmentation procedure. Using the Erasmus University Medical Center standard procedure, HTP was applied to these models and compared to HTP for commonly used surrogate models.Results: Although this study was aimed at presenting the EVPR database, our study illustrates that there is a non-negligible difference in the predicted SAR patterns between patient models and homogeneous phantom-based surrogate models. We further demonstrate the difference between actual and simplified target volumes being used today.Conclusion: Our study describes the EVPR for the research community as a first step toward standardization of hyperthermia simulation studies.
Collapse
Affiliation(s)
- Gennaro G Bellizzi
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Kemal Sumser
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Iva VilasBoas-Ribeiro
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Sergio Curto
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Tomas Drizdal
- Department of Biomedical Technology, Czech Technical University in Prague, Prague, Czech Republic
| | - Gerard C van Rhoon
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Martine Franckena
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands
| | - Margarethus M Paulides
- Hyperthermia Unit, Department of Radiation Oncology, Erasmus University Medical Center, Rotterdam, The Netherlands.,Department of Electrical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands
| |
Collapse
|
76
|
Yao A, Goren T, Samaras T, Kuster N, Kainz W. Radiofrequency-induced heating of broken and abandoned implant leads during magnetic resonance examinations. Magn Reson Med 2021; 86:2156-2164. [PMID: 34080721 PMCID: PMC8362172 DOI: 10.1002/mrm.28836] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Revised: 04/15/2021] [Accepted: 04/21/2021] [Indexed: 12/21/2022]
Abstract
Purpose The risks of RF‐induced heating of active implantable medical device (AIMD) leads during MR examinations must be well understood and realistically assessed. In this study, we evaluate the potential additional risks of broken and abandoned (cut) leads. Methods First, we defined a generic AIMD with a metallic implantable pulse generator (IPG) and a 100‐cm long lead containing 1 or 2 wires. Next, we numerically estimated the deposited in vitro lead‐tip power for an intact lead, as well as with wire breaks placed at 10 cm intervals. We studied the effect of the break size (wire gap width), as well as the presence of an intact wire parallel to the broken wire, and experimentally validated the numeric results for the configurations with maximum deposited in vitro lead‐tip power. Finally, we performed a Tier 3 assessment of the deposited in vivo lead‐tip power for the intact and broken lead in 4 high resolution virtual population anatomic models for over 54,000 MR examination scenarios. Results The enhancement of the deposited lead‐tip power for the broken leads, compared to the intact lead, reached 30‐fold in isoelectric exposure, and 16‐fold in realistic clinical exposures. The presence of a nearby intact wire, or even a nearby broken wire, reduced this enhancement factor to <7‐fold over the intact lead. Conclusion Broken and abandoned leads can pose increased risk of RF‐induced lead‐tip heating to patients undergoing MR examinations. The potential enhancement of deposited in vivo lead‐tip power depends on location and type of the wire break, lead design, and clinical routing of the lead, and should be carefully considered when performing risk assessment for MR examinations and MR conditional labeling.
Collapse
Affiliation(s)
- Aiping Yao
- Foundation of Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - Tolga Goren
- Foundation of Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - Theodoros Samaras
- Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Niels Kuster
- Foundation of Research on Information Technologies in Society (IT'IS), Zurich, Switzerland.,Department of Information Technology and Electrical Engineering, ETH Zurich, Zurich, Switzerland
| | - Wolfgang Kainz
- Center for Devices and Radiological Health, Food and Drug Administration (FDA), Silver Spring, Maryland, USA
| |
Collapse
|
77
|
Jung KJ, Mandija S, Kim JH, Ryu K, Jung S, Cui C, Kim SY, Park M, van den Berg CAT, Kim DH. Improving phase-based conductivity reconstruction by means of deep learning-based denoising of B 1 + phase data for 3T MRI. Magn Reson Med 2021; 86:2084-2094. [PMID: 33949721 DOI: 10.1002/mrm.28826] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 03/28/2021] [Accepted: 04/13/2021] [Indexed: 12/24/2022]
Abstract
PURPOSE To denoise B 1 + phase using a deep learning method for phase-based in vivo electrical conductivity reconstruction in a 3T MR system. METHODS For B 1 + phase deep-learning denoising, a convolutional neural network (U-net) was chosen. Training was performed on data sets from 10 healthy volunteers. Input data were the real and imaginary components of single averaged spin-echo data (SNR = 45), which was used to approximate the B 1 + phase. For label data, multiple signal-averaged spin-echo data (SNR = 128) were used. Testing was performed on in silico and in vivo data. Reconstructed conductivity maps were derived using phase-based conductivity reconstructions. Additionally, we investigated the usability of the network to various SNR levels, imaging contrasts, and anatomical sites (ie, T1 , T2 , and proton density-weighted brain images and proton density-weighted breast images. In addition, conductivity reconstructions from deep learning-based denoised data were compared with conventional image filters, which were used for data denoising in electrical properties tomography (ie, the Gaussian filtering and the Savitzky-Golay filtering). RESULTS The proposed deep learning-based denoising approach showed improvement for B 1 + phase for both in silico and in vivo experiments with reduced quantitative error measures compared with other methods. Subsequently, this resulted in an improvement of reconstructed conductivity maps from the denoised B 1 + phase with deep learning. CONCLUSION The results suggest that the proposed approach can be used as an alternative preprocessing method to denoise B 1 + maps for phase-based conductivity reconstruction without relying on image filters or signal averaging.
Collapse
Affiliation(s)
- Kyu-Jin Jung
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Stefano Mandija
- Computational Imaging Group for MR Diagnostic & Therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.,Department of Radiotherapy, Division of Imaging & Oncology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Jun-Hyeong Kim
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Kanghyun Ryu
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea.,Department of Radiology, Stanford University, Stanford, California, USA
| | - Soozy Jung
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Chuanjiang Cui
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Soo-Yeon Kim
- Department of Radiology, Seoul National University Hospital, Seoul, Republic of Korea
| | - Mina Park
- Department of Radiology, Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Republic of Korea
| | - Cornelis A T van den Berg
- Computational Imaging Group for MR Diagnostic & Therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.,Department of Radiotherapy, Division of Imaging & Oncology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Dong-Hyun Kim
- Department of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| |
Collapse
|
78
|
Fum WKS, Wong JHD, Tan LK. Monte Carlo-based patient internal dosimetry in fluoroscopy-guided interventional procedures: A review. Phys Med 2021; 84:228-240. [PMID: 33849785 DOI: 10.1016/j.ejmp.2021.03.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Revised: 02/18/2021] [Accepted: 03/03/2021] [Indexed: 11/27/2022] Open
Abstract
PURPOSE This systematic review aims to understand the dose estimation approaches and their major challenges. Specifically, we focused on state-of-the-art Monte Carlo (MC) methods in fluoroscopy-guided interventional procedures. METHODS All relevant studies were identified through keyword searches in electronic databases from inception until September 2020. The searched publications were reviewed, categorised and analysed based on their respective methodology. RESULTS Hundred and one publications were identified which utilised existing MC-based applications/programs or customised MC simulations. Two outstanding challenges were identified that contribute to uncertainties in the virtual simulation reconstruction. The first challenge involves the use of anatomical models to represent individuals. Currently, phantom libraries best balance the needs of clinical practicality with those of specificity. However, mismatches of anatomical variations including body size and organ shape can create significant discrepancies in dose estimations. The second challenge is that the exact positioning of the patient relative to the beam is generally unknown. Most dose prediction models assume the patient is located centrally on the examination couch, which can lead to significant errors. CONCLUSION The continuing rise of computing power suggests a near future where MC methods become practical for routine clinical dosimetry. Dynamic, deformable phantoms help to improve patient specificity, but at present are only limited to adjustment of gross body volume. Dynamic internal organ displacement or reshaping is likely the next logical frontier. Image-based alignment is probably the most promising solution to enable this, but it must be automated to be clinically practical.
Collapse
Affiliation(s)
- Wilbur K S Fum
- Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia; Division of Radiological Sciences, Singapore General Hospital, Outram Rd, Singapore 169608, Singapore.
| | - Jeannie Hsiu Ding Wong
- Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia.
| | - Li Kuo Tan
- Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, Kuala Lumpur 50603, Malaysia.
| |
Collapse
|
79
|
Coil Design of a Wireless Power-Transfer Receiver Integrated into a Left Ventricular Assist Device. ELECTRONICS 2021. [DOI: 10.3390/electronics10080874] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
This study deals with the design of a near-field wireless power transfer (WPT) system applied to a left ventricular assist device (LVAD) to treat patients with heart-failure problems. An LVAD is an implanted electrically driven pump connected to the heart and is traditionally powered by batteries external to the human body via a percutaneous driveline cable. The main challenge of wirelessly powering an LVAD implanted deep in the human body is to transfer relatively high power with high efficiency levels. Here the optimal design of the primary and secondary WPT coils is proposed to improve the performance of the WPT, avoiding possible safety problems of electromagnetic fields (EMF). As a main result, an average power of 5 W is continuously delivered to the LVAD by the WPT system working at 6.78 MHz with a total (DC–to–DC) efficiency of approximately 65% for the worst-case configuration.
Collapse
|
80
|
Jagielski K, Kraus T, Stunder D. Interference of cardiovascular implantable electronic devices by static electric and magnetic fields. Expert Rev Med Devices 2021; 18:395-405. [PMID: 33710950 DOI: 10.1080/17434440.2021.1902802] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
Introduction: Electromagnetic interference (EMI) of cardiovascular implantable electronic devices (CIED) can lead to malfunctions and pose a danger for implant carriers. The increased use of DC technologies, e.g. in electric mobility, creates more static fields representing an increasing hazard for implant carriers.Areas covered: A combination of approaches was used to determine thresholds for EMI by static fields. A literature search was conducted to identify relevant EMI mechanisms and to extract possible thresholds. The literature search revealed four interference mechanisms caused by static magnetic fields and none for static electric fields. Due to the scarce information on motion-induced EMI, numerical simulations were performed to obtain a threshold. The simulation results were evaluated using medical product standards and benchmark tests on commercially available CIEDs. The results show that motion-induced interference should not occur below the activation of the magnetic safety switch (reed switch or Hall-effect sensor, MSS).Expert opinion: The determined threshold for motion-induced EMI at 24.8 mT shows that the MSS activation is still the most relevant mechanism that can occur at 0.8 mT. Limit values for the general population do not protect implant carriers from EMI.
Collapse
Affiliation(s)
- Kai Jagielski
- Research Center for Bioelectromagnetic Interaction - Femu, Institute for Occupational, Social and Environmental Medicine, University Hospital RWTH Aachen, Aachen, Germany
| | - Thomas Kraus
- Research Center for Bioelectromagnetic Interaction - Femu, Institute for Occupational, Social and Environmental Medicine, University Hospital RWTH Aachen, Aachen, Germany
| | - Dominik Stunder
- Research Center for Bioelectromagnetic Interaction - Femu, Institute for Occupational, Social and Environmental Medicine, University Hospital RWTH Aachen, Aachen, Germany
| |
Collapse
|
81
|
Gregersen F, Göksu C, Schaefers G, Xue R, Thielscher A, Hanson LG. Safety evaluation of a new setup for transcranial electric stimulation during magnetic resonance imaging. Brain Stimul 2021; 14:488-497. [PMID: 33706007 DOI: 10.1016/j.brs.2021.02.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 01/07/2021] [Accepted: 02/26/2021] [Indexed: 01/22/2023] Open
Abstract
BACKGROUND Transcranial electric stimulation during MR imaging can introduce safety issues due to coupling of the RF field with the stimulation electrodes and leads. OBJECTIVE To optimize the stimulation setup for MR current density imaging (MRCDI) and increase maximum stimulation current, a new low-conductivity (σ = 29.4 S/m) lead wire is designed and tested. METHOD The antenna effect was simulated to investigate the effect of lead conductivity. Subsequently, specific absorption rate (SAR) simulations for realistic lead configurations with low-conductivity leads and two electrode types were performed at 128 MHz and 298 MHz being the Larmor frequencies of protons at 3T and 7T. Temperature measurements were performed during MRI using high power deposition sequences to ensure that the electrodes comply with MRI temperature regulations. RESULTS The antenna effect was found for copper leads at ¼ RF wavelength and could be reliably eliminated using low-conductivity leads. Realistic lead configurations increased the head SAR and the local head SAR at the electrodes only minimally. The highest temperatures were measured on the rings of center-surround electrodes, while circular electrodes showed little heating. No temperature increase above the safety limit of 39 °C was observed. CONCLUSION Coupling to the RF field can be reliably prevented by low-conductivity leads, enabling cable paths optimal for MRCDI. Compared to commercial copper leads with safety resistors, the low-conductivity leads had lower total impedance, enabling the application of higher currents without changing stimulator design. Attention must be paid to electrode pads.
Collapse
Affiliation(s)
- Fróði Gregersen
- Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark; Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark; Sino-Danish Center for Education and Research, Aarhus, Denmark; University of Chinese Academic of Sciences, Beijing, 100049, China
| | - Cihan Göksu
- Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark; High-Field Magnetic Resonance Center, Max-Planck-Institute for Biological Cybernetics, Tübingen, Germany
| | - Gregor Schaefers
- MRI-STaR-Magnetic Resonance Institute for Safety, Technology and Research GmbH, Gelsenkirchen, Germany; MR:comp GmbH, MR Safety Testing Laboratory, Gelsenkirchen, Germany
| | - Rong Xue
- State Key Laboratory of Brain and Cognitive Science, Beijing MRI Center for Brain Research, Institute of Biophysics, Chinese Academy of Sciences, Beijing, 100101, China; University of Chinese Academic of Sciences, Beijing, 100049, China; Beijing Institute for Brain Disorders, Beijing, 100053, China
| | - Axel Thielscher
- Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark; Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark
| | - Lars G Hanson
- Section for Magnetic Resonance, DTU Health Tech, Technical University of Denmark, Kgs Lyngby, Denmark; Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Amager and Hvidovre, Hvidovre, Denmark.
| |
Collapse
|
82
|
Abstract
Time-reversal (TR) is a known wideband array beam-forming technique that has been suggested as a treatment planning alternative in deep microwave hyperthermia for cancer treatment. While the aim in classic TR is to focus the energy at a specific point within the target, no assumptions are made on secondary lobes that might arise in the healthy tissues. These secondary lobes, together with tissue heterogeneity, may result in hot-spots (HSs), which are known to limit the efficiency of the thermal dose delivery to the tumor. This paper proposes a novel wideband TR focusing method that iteratively shifts the focus away from HSs and towards cold-spots from an initial TR solution, a procedure that improves tumor coverage and reduces HSs. We verify this method on two different applicator topologies and several target volume configurations. The algorithm is deterministic and runs within seconds, enabling its use for real-time applications. At the same time, it yields results comparable to those obtained with global stochastic optimizers such as Particle Swarm.
Collapse
Affiliation(s)
- Massimiliano Zanoli
- Dept. Electrical Engineering, Chalmers University of Technology, Gothenburg, SE, Sweden
| | - Hana Dobšíček Trefná
- Dept. Electrical Engineering, Chalmers University of Technology, Gothenburg, SE, Sweden
| |
Collapse
|
83
|
McCullough JWS, Richardson RA, Patronis A, Halver R, Marshall R, Ruefenacht M, Wylie BJN, Odaker T, Wiedemann M, Lloyd B, Neufeld E, Sutmann G, Skjellum A, Kranzlmüller D, Coveney PV. Towards blood flow in the virtual human: efficient self-coupling of HemeLB. Interface Focus 2021; 11:20190119. [PMID: 33335704 PMCID: PMC7739917 DOI: 10.1098/rsfs.2019.0119] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/23/2020] [Indexed: 11/12/2022] Open
Abstract
Many scientific and medical researchers are working towards the creation of a virtual human—a personalized digital copy of an individual—that will assist in a patient’s diagnosis, treatment and recovery. The complex nature of living systems means that the development of this remains a major challenge. We describe progress in enabling the HemeLB lattice Boltzmann code to simulate 3D macroscopic blood flow on a full human scale. Significant developments in memory management and load balancing allow near linear scaling performance of the code on hundreds of thousands of computer cores. Integral to the construction of a virtual human, we also outline the implementation of a self-coupling strategy for HemeLB. This allows simultaneous simulation of arterial and venous vascular trees based on human-specific geometries.
Collapse
Affiliation(s)
- J W S McCullough
- Centre for Computational Science, Department of Chemistry, University College London, London, UK
| | - R A Richardson
- Centre for Computational Science, Department of Chemistry, University College London, London, UK
| | - A Patronis
- Centre for Computational Science, Department of Chemistry, University College London, London, UK.,Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany
| | - R Halver
- Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany
| | - R Marshall
- SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN, USA
| | - M Ruefenacht
- SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN, USA
| | - B J N Wylie
- Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany
| | - T Odaker
- Leibniz Supercomputing Centre, Leibniz-Rechenzentrum (LRZ), Garching, Germany
| | - M Wiedemann
- Leibniz Supercomputing Centre, Leibniz-Rechenzentrum (LRZ), Garching, Germany
| | - B Lloyd
- Foundation for Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - E Neufeld
- Foundation for Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - G Sutmann
- Jülich Supercomputing Centre, Forschungszentrum Jülich, Jülich, Germany.,ICAMS, Ruhr-University Bochum, Bochum, Germany
| | - A Skjellum
- SimCenter, University of Tennessee at Chattanooga, Chattanooga, TN, USA
| | - D Kranzlmüller
- Leibniz Supercomputing Centre, Leibniz-Rechenzentrum (LRZ), Garching, Germany
| | - P V Coveney
- Centre for Computational Science, Department of Chemistry, University College London, London, UK.,Informatics Institute, University of Amsterdam, Amsterdam, The Netherlands
| |
Collapse
|
84
|
Li X, Pan JW, Avdievich NI, Hetherington HP, Rispoli JV. Electromagnetic simulation of a 16-channel head transceiver at 7 T using circuit-spatial optimization. Magn Reson Med 2021; 85:3463-3478. [PMID: 33533500 DOI: 10.1002/mrm.28672] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2020] [Revised: 12/16/2020] [Accepted: 12/17/2020] [Indexed: 11/07/2022]
Abstract
PURPOSE With increased interest in parallel transmission in ultrahigh-field MRI, methods are needed to correctly calculate the S-parameters and complex field maps of the parallel transmission coil. We present S-parameters paired with spatial field optimization to fully simulate a double-row 16-element transceiver array for brain MRI at 7 T. METHODS We implemented a closed-form equation of the coil S-parameters and overall spatial B 1 + field. We minimized a cost function, consisting of coil S-parameters and the B 1 + homogeneity in brain tissue, by optimizing transceiver components, including matching, decoupling circuits, and lumped capacitors. With this, we are able to compare the in silico results determined with and without B 1 + homogeneity weighting. Using the known voltage range from the host console, we reconstructed the B 1 + maps of the array and performed RF shimming with four realistic head models. RESULTS As performed with B 1 + homogeneity weighting, the optimized coil circuit components were highly consistent over the four heads, producing well-tuned, matched, and decoupled coils. The mean peak forward powers and B 1 + statistics for the head models are consistent with in vivo human results (N = 8). There are systematic differences in the transceiver components as optimized with or without B 1 + homogeneity weighting, resulting in an improvement of 28.4 ± 7.5% in B 1 + homogeneity with a small 1.9 ± 1.5% decline in power efficiency. CONCLUSION This co-simulation methodology accurately simulates the transceiver, predicting consistent S-parameters, component values, and B 1 + field. The RF shimming of the calculated field maps match the in vivo performance.
Collapse
Affiliation(s)
- Xin Li
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA
| | - Jullie W Pan
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Nikolai I Avdievich
- High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany
| | - Hoby P Hetherington
- Department of Radiology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Joseph V Rispoli
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana, USA
- School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana, USA
| |
Collapse
|
85
|
Birks LE, van Wel L, Liorni I, Pierotti L, Guxens M, Huss A, Foerster M, Capstick M, Eeftens M, El Marroun H, Estarlich M, Gallastegi M, Safont LG, Joseph W, Santa-Marina L, Thielens A, Torrent M, Vrijkotte T, Wiart J, Röösli M, Cardis E, Vermeulen R, Vrijheid M. Radiofrequency electromagnetic fields from mobile communication: Description of modeled dose in brain regions and the body in European children and adolescents. ENVIRONMENTAL RESEARCH 2021; 193:110505. [PMID: 33245886 DOI: 10.1016/j.envres.2020.110505] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/16/2019] [Revised: 11/02/2020] [Accepted: 11/17/2020] [Indexed: 06/11/2023]
Abstract
BACKGROUND Little is known about radiofrequency electromagnetic fields (RF) from mobile technology and resulting dose in young people. We describe modeled integrated RF dose in European children and adolescents combining own mobile device use and surrounding sources. METHODS Using an integrated RF model, we estimated the daily RF dose in the brain (whole-brain, cerebellum, frontal lobe, midbrain, occipital lobe, parietal lobe, temporal lobes) and the whole-body in 8358 children (ages 8-12) and adolescents (ages 14-18) from the Netherlands, Spain, and Switzerland during 2012-2016. The integrated model estimated RF dose from near-field sources (digital enhanced communication technology (DECT) phone, mobile phone, tablet, and laptop) and far-field sources (mobile phone base stations via 3D-radiowave modeling or RF measurements). RESULTS Adolescents were more frequent mobile phone users and experienced higher modeled RF doses in the whole-brain (median 330.4 mJ/kg/day) compared to children (median 81.8 mJ/kg/day). Children spent more time using tablets or laptops compared to adolescents, resulting in higher RF doses in the whole-body (median whole-body dose of 81.8 mJ/kg/day) compared to adolescents (41.9 mJ/kg/day). Among brain regions, temporal lobes received the highest RF dose (medians of 274.9 and 1786.5 mJ/kg/day in children and adolescents, respectively) followed by the frontal lobe. In most children and adolescents, calling on 2G networks was the main contributor to RF dose in the whole-brain (medians of 31.1 and 273.7 mJ/kg/day, respectively). CONCLUSION This first large study of RF dose to the brain and body of children and adolescents shows that mobile phone calls on 2G networks are the main determinants of brain dose, especially in temporal and frontal lobes, whereas whole-body doses were mostly determined by tablet and laptop use. The modeling of RF doses provides valuable input to epidemiological research and to potential risk management regarding RF exposure in young people.
Collapse
Affiliation(s)
- Laura Ellen Birks
- ISGlobal, Barcelona, Spain; Pompeu Fabra University, Barcelona, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain
| | - Luuk van Wel
- Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, the Netherlands
| | - Ilaria Liorni
- Foundation for Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - Livia Pierotti
- ISGlobal, Barcelona, Spain; Pompeu Fabra University, Barcelona, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain
| | - Mònica Guxens
- ISGlobal, Barcelona, Spain; Pompeu Fabra University, Barcelona, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain; Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Centre, Rotterdam, the Netherlands
| | - Anke Huss
- Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, the Netherlands
| | - Milena Foerster
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
| | - Myles Capstick
- Foundation for Research on Information Technologies in Society (IT'IS), Zurich, Switzerland
| | - Marloes Eeftens
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
| | - Hanan El Marroun
- Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Centre, Rotterdam, the Netherlands; Department of Pediatrics, Erasmus MC, the Netherlands; Department of Psychology, Education and Child Studies - Erasmus University Rotterdam, the Netherlands
| | - Marisa Estarlich
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain; Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Valencia, Spain; Faculty of Nursing and Chiropody, Universitat de València, Spain
| | - Mara Gallastegi
- BIODONOSTIA Health Research Institute, Dr. Begiristain Pasealekua, San Sebastian, Spain
| | - Llúcia González Safont
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain; Epidemiology and Environmental Health Joint Research Unit, FISABIO-Universitat Jaume I-Universitat de València, Valencia, Spain
| | - Wout Joseph
- Department of Information Technology, Ghent University/IMEC, Technologiepark 126, Ghent, 9052, Belgium
| | - Loreto Santa-Marina
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain; BIODONOSTIA Health Research Institute, Dr. Begiristain Pasealekua, San Sebastian, Spain; Department of Health of the Basque Government, Public Health Division of Gipuzkoa, Donostia-San Sebastián, Spain
| | - Arno Thielens
- Department of Information Technology, Ghent University/IMEC, Technologiepark 126, Ghent, 9052, Belgium
| | - Maties Torrent
- Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain
| | - Tanja Vrijkotte
- Department of Public Health, Amsterdam UMC, University of Amsterdam, Amsterdam Public Health Research Institute, Amsterdam, the Netherlands
| | - Joe Wiart
- Télécom ParisTech, LTCI University Paris Saclay, Chair C2M, Paris, France
| | - Martin Röösli
- Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
| | - Elisabeth Cardis
- ISGlobal, Barcelona, Spain; Pompeu Fabra University, Barcelona, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain
| | - Roel Vermeulen
- Institute for Risk Assessment Sciences (IRAS), Utrecht University, Utrecht, the Netherlands; Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, the Netherlands; School of Public Health, Imperial College London, London, UK
| | - Martine Vrijheid
- ISGlobal, Barcelona, Spain; Pompeu Fabra University, Barcelona, Spain; Spanish Consortium for Research on Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain.
| |
Collapse
|
86
|
Fagan AJ, Bitz AK, Björkman-Burtscher IM, Collins CM, Kimbrell V, Raaijmakers AJ. 7T MR Safety. J Magn Reson Imaging 2021; 53:333-346. [PMID: 32830900 PMCID: PMC8170917 DOI: 10.1002/jmri.27319] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Revised: 07/21/2020] [Accepted: 07/22/2020] [Indexed: 12/11/2022] Open
Abstract
Magnetic resonance imaging and spectroscopy (MRI/MRS) at 7T represents an exciting advance in MR technology, with intriguing possibilities to enhance image spatial, spectral, and contrast resolution. To ensure the safe use of this technology while still harnessing its potential, clinical staff and researchers need to be cognizant of some safety concerns arising from the increased magnetic field strength and higher Larmor frequency. The higher static magnetic fields give rise to enhanced transient bioeffects and an increased risk of adverse incidents related to electrically conductive implants. Many technical challenges remain and the continuing rapid pace of development of 7T MRI/MRS is likely to present further challenges to ensuring safety of this technology in the years ahead. The recent regulatory clearance for clinical diagnostic imaging at 7T will likely increase the installed base of 7T systems, particularly in hospital environments with little prior ultrahigh-field MR experience. Informed risk/benefit analyses will be required, particularly where implant manufacturer-published 7T safety guidelines for implants are unavailable. On behalf of the International Society for Magnetic Resonance in Medicine, the aim of this article is to provide a reference document to assist institutions developing local institutional policies and procedures that are specific to the safe operation of 7T MRI/MRS. Details of current 7T technology and the physics underpinning its functionality are reviewed, with the aim of supporting efforts to expand the use of 7T MRI/MRS in both research and clinical environments. Current gaps in knowledge are also identified, where additional research and development are required. Level of Evidence 5 Technical Efficacy 2 J. MAGN. RESON. IMAGING 2021;53:333-346.
Collapse
Affiliation(s)
- Andrew J. Fagan
- Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA
| | - Andreas K. Bitz
- Faculty of Electrical Engineering and Information Technology, FH Aachen - University of Applied Sciences, Aachen, Germany
| | - Isabella M. Björkman-Burtscher
- Department of Radiology, University of Gothenburg, Sahlgrenska Academy, Sahlgrenska University Hospital, Gothenburg, Sweden
| | - Christopher M. Collins
- Center for Advanced Imaging Innovation and Research, NYU Langone Medical Center, New York, New York, USA
| | - Vera Kimbrell
- Department of Radiology, Brigham and Women’s Hospital, Boston, Massachusetts, USA
| | | | | |
Collapse
|
87
|
Haggmark I, Shaker K, Hertz HM. In Silico Phase-Contrast X-Ray Imaging of Anthropomorphic Voxel-Based Phantoms. IEEE TRANSACTIONS ON MEDICAL IMAGING 2021; 40:539-548. [PMID: 33055024 DOI: 10.1109/tmi.2020.3031318] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Propagation-based phase-contrast X-ray imaging is an emerging technique that can improve dose efficiency in clinical imaging. In silico tools are key to understanding the fundamental imaging mechanisms and develop new applications. Here, due to the coherent nature of the phase-contrast effects, tools based on wave propagation (WP) are preferred over Monte Carlo (MC) based methods. WP simulations require very high wave-front sampling which typically limits simulations to small idealized objects. Virtual anthropomorphic voxel-based phantoms are typically provided with a resolution lower than imposed sampling requirements and, thus, cannot be directly translated for use in WP simulations. In the present paper we propose a general strategy to enable the use of these phantoms for WP simulations. The strategy is based on upsampling in the 3D domain followed by projection resulting in high-resolution maps of the projected thickness for each phantom material. These maps can then be efficiently used for simulations of Fresnel diffraction to generate in silico phase-contrast X-ray images. We demonstrate the strategy on an anthropomorphic breast phantom to simulate propagation-based phase-contrast mammography using a laboratory micro-focus X-ray source.
Collapse
|
88
|
Colella M, Paffi A, De Santis V, Apollonio F, Liberti M. Effect of skin conductivity on the electric field induced by transcranial stimulation techniques in different head models. Phys Med Biol 2021; 66:035010. [PMID: 33496268 DOI: 10.1088/1361-6560/abcde7] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
This study aims at quantifying the effect that using different skin conductivity values has on the estimation of the electric (E)-field distribution induced by transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) in the brain of two anatomical models. The induced E-field was calculated with numerical simulations inside MIDA and Duke models, assigning to the skin a conductivity value estimated from a multi-layered skin model and three values taken from literature. The effect of skin conductivity variations on the local E-field induced by tDCS in the brain was up to 70%. In TMS, minor local differences, in the order of 20%, were obtained in regions of interest for the onset of possible side effects. Results suggested that an accurate model of the skin is necessary in all numerical studies that aim at precisely estimating the E-field induced during TMS and tDCS applications. This also highlights the importance of further experimental studies on human skin characterization, especially at low frequencies.
Collapse
Affiliation(s)
- Micol Colella
- Department of Information Engineering, Electronics and Telecommunications (DIET), University of Rome 'La Sapienza', Rome, Italy
| | - Alessandra Paffi
- Department of Information Engineering, Electronics and Telecommunications (DIET), University of Rome 'La Sapienza', Rome, Italy
| | - Valerio De Santis
- Department of Industrial and Information Engineering and Economics (DIIEE), University of L'Aquila, L'Aquila, Italy
| | - Francesca Apollonio
- Department of Information Engineering, Electronics and Telecommunications (DIET), University of Rome 'La Sapienza', Rome, Italy
| | - Micaela Liberti
- Department of Information Engineering, Electronics and Telecommunications (DIET), University of Rome 'La Sapienza', Rome, Italy
| |
Collapse
|
89
|
Jeong H, Ntolkeras G, Alhilani M, Atefi SR, Zöllei L, Fujimoto K, Pourvaziri A, Lev MH, Grant PE, Bonmassar G. Development, validation, and pilot MRI safety study of a high-resolution, open source, whole body pediatric numerical simulation model. PLoS One 2021; 16:e0241682. [PMID: 33439896 PMCID: PMC7806143 DOI: 10.1371/journal.pone.0241682] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2020] [Accepted: 10/19/2020] [Indexed: 11/30/2022] Open
Abstract
Numerical body models of children are used for designing medical devices, including but not limited to optical imaging, ultrasound, CT, EEG/MEG, and MRI. These models are used in many clinical and neuroscience research applications, such as radiation safety dosimetric studies and source localization. Although several such adult models have been reported, there are few reports of full-body pediatric models, and those described have several limitations. Some, for example, are either morphed from older children or do not have detailed segmentations. Here, we introduce a 29-month-old male whole-body native numerical model, "MARTIN", that includes 28 head and 86 body tissue compartments, segmented directly from the high spatial resolution MRI and CT images. An advanced auto-segmentation tool was used for the deep-brain structures, whereas 3D Slicer was used to segment the non-brain structures and to refine the segmentation for all of the tissue compartments. Our MARTIN model was developed and validated using three separate approaches, through an iterative process, as follows. First, the calculated volumes, weights, and dimensions of selected structures were adjusted and confirmed to be within 6% of the literature values for the 2-3-year-old age-range. Second, all structural segmentations were adjusted and confirmed by two experienced, sub-specialty certified neuro-radiologists, also through an interactive process. Third, an additional validation was performed with a Bloch simulator to create synthetic MR image from our MARTIN model and compare the image contrast of the resulting synthetic image with that of the original MRI data; this resulted in a "structural resemblance" index of 0.97. Finally, we used our model to perform pilot MRI safety simulations of an Active Implantable Medical Device (AIMD) using a commercially available software platform (Sim4Life), incorporating the latest International Standards Organization guidelines. This model will be made available on the Athinoula A. Martinos Center for Biomedical Imaging website.
Collapse
Affiliation(s)
- Hongbae Jeong
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Georgios Ntolkeras
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Michel Alhilani
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States of America
- Department of Medicine, Charing Cross Hospital, Imperial College Healthcare NHS Trust, London, United Kingdom
| | - Seyed Reza Atefi
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Lilla Zöllei
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Kyoko Fujimoto
- Center for Devices and Radiological Health, U. S. Food and Drug Administration, Silver Spring, MD, United States of America
| | - Ali Pourvaziri
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Michael H. Lev
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| | - P. Ellen Grant
- Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children’s Hospital, Harvard Medical School, Boston, MA, United States of America
| | - Giorgio Bonmassar
- Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
- Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States of America
| |
Collapse
|
90
|
Fagan AJ, Jacobs PS, Hulshizer TC, Rossman PJ, Frick MA, Amrami KK, Felmlee JP. 7T MR Thermometry technique for validation of system-predicted SAR with a home-built radiofrequency wrist coil. Med Phys 2020; 48:781-790. [PMID: 33294999 DOI: 10.1002/mp.14641] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 11/03/2020] [Accepted: 11/30/2020] [Indexed: 11/12/2022] Open
Abstract
PURPOSE A 7T magnetic resonance thermometry (MRT) technique was developed to validate the conversion factor between the system-measured transmitted radiofrequency (RF) power into a home-built RF wrist coil with the system-predicted SAR value. The conversion factor for a new RF coil developed for ultra high magnetic field MRI systems is used to ensure that regulatory limits on RF energy deposition in tissue, specifically the local 10g-averaged specific absorption rate (SAR10g ), are not exceeded. MRT can be used to validate this factor by ensuring that MRT-measured SAR values do not exceed those predicted by the system. METHODS A 14-cm diameter high-pass birdcage RF coil was built to image the wrist at 7T. A high spatial and temporal resolution dual-echo gradient echo MRT technique, incorporating quasi-simultaneous RF-induced heating and temperature change measurements using the proton resonance frequency method, was developed. The technique allowed for high-temperature resolution measurements (~±0.1°C) to be performed every 20 s over a 4-min heating period, with high spatial resolution (2.56 mm3 voxel size) and avoiding phase discontinuities arising from severe magnetic susceptibility-induced B0 inhomogeneities. Magnetic resonance thermometry was performed on a phantom made from polyvinylpyrrolidone to mimic the dielectric properties of muscle tissue at 297.2 MHz. Temperature changes measured with MRT and four fiber optic temperature sensors embedded in the phantom were compared. Electromagnetic simulations of the coil and phantom were developed and validated via comparison of simulated and measured B1 + maps in the phantom. The position of maximum SAR within the coil was determined from simulations, and MRT was performed within a wrist-sized piece of meat positioned at that SAR hotspot location. MRT-measured and system-predicted SAR values for the phantom and meat were compared. RESULTS Temperature change measurements from MRT matched closely to those from the fiber optic temperature sensors. The simulations were validated via close correlation between the simulated and MRT-measured B1 + and SAR maps. Using a coil conversion factor of 2 kg-1 , MRT-measured point-SAR values did not exceed the system-predicted SAR10g in either the uniform phantom or in the piece of meat mimicking the wrist located at the SAR hotspot location. CONCLUSIONS A highly accurate MRT technique with high spatial and temporal resolution was developed. This technique can be used to ensure that system-predicted SAR values are not exceeded in practice, thereby providing independent validation of SAR levels delivered by a newly built RF wrist coil. The MRT technique is readily generalizable to perform safety evaluations for other RF coils at 7T.
Collapse
Affiliation(s)
- Andrew J Fagan
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Paul S Jacobs
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Thomas C Hulshizer
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Phillip J Rossman
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Matthew A Frick
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Kimberly K Amrami
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| | - Joel P Felmlee
- Department of Radiology, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA
| |
Collapse
|
91
|
Meliadò EF, Sbrizzi A, van den Berg CAT, Luijten PR, Raaijmakers AJE. Real-time assessment of potential peak local specific absorption rate value without phase monitoring: Trigonometric maximization method for worst-case local specific absorption rate determination. Magn Reson Med 2020; 85:3420-3433. [PMID: 33350525 PMCID: PMC7986921 DOI: 10.1002/mrm.28635] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 11/12/2020] [Accepted: 11/16/2020] [Indexed: 12/16/2022]
Abstract
Purpose Multi‐transmit MRI systems are typically equipped with dedicated hardware to sample the reflected/lost power in the transmit channels. After extensive calibration, the amplitude and phase of the signal at the feed of each array element can be accurately determined. However, determining the phase is more difficult and monitoring errors can lead to a hazardous peak local specific absorption rate (pSAR10g) underestimation. For this purpose, methods were published for online maximum potential pSAR10g estimation without relying on phase monitoring, but these methods produce considerable overestimation. We present a trigonometric maximization method to determine the actual worst‐case pSAR10g without any overestimation. Theory and Method The proposed method takes advantage of the sinusoidal relation between the SAR10g in each voxel and the phases of input signals, to return the maximum achievable SAR10g in a few iterations. The method is applied to determine the worst‐case pSAR10g for three multi‐transmit array configurations at 7T: (1) body array with eight fractionated dipoles; (2) head array with eight fractionated dipoles; (3) head array with eight rectangular loops. The obtained worst‐case pSAR10g values are compared with the pSAR10g values determined with a commonly used method and with a more efficient method based on reference‐phases. Results For each voxel, the maximum achievable SAR10g is determined in less than 0.1 ms. Compared to the reference‐phases‐based method, the proposed method reduces the mean overestimation of the actual pSAR10g up to 52%, while never underestimating the true pSAR10g. Conclusion The proposed method can widely improve the performance of parallel transmission MRI systems without phase monitoring.
Collapse
Affiliation(s)
- Ettore Flavio Meliadò
- Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands.,Computational Imaging Group for MR diagnostics & therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.,Tesla Dynamic Coils BV, Zaltbommel, the Netherlands
| | - Alessandro Sbrizzi
- Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands.,Computational Imaging Group for MR diagnostics & therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Cornelis A T van den Berg
- Computational Imaging Group for MR diagnostics & therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.,Department of Radiotherapy, Division of Imaging & Oncology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Peter R Luijten
- Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands
| | - Alexander J E Raaijmakers
- Department of Radiology, University Medical Center Utrecht, Utrecht, the Netherlands.,Computational Imaging Group for MR diagnostics & therapy, Center for Image Sciences, University Medical Center Utrecht, Utrecht, the Netherlands.,Biomedical Image Analysis, Department Biomedical Engineering, Eindhoven University of Technology, Eindhoven, the Netherlands
| |
Collapse
|
92
|
Dietrich S, Aigner CS, Kolbitsch C, Mayer J, Ludwig J, Schmidt S, Schaeffter T, Schmitter S. 3D Free-breathing multichannel absolute B 1 + Mapping in the human body at 7T. Magn Reson Med 2020; 85:2552-2567. [PMID: 33283915 DOI: 10.1002/mrm.28602] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 10/23/2020] [Accepted: 10/25/2020] [Indexed: 12/13/2022]
Abstract
PURPOSE To introduce and investigate a method for free-breathing three-dimensional (3D) B 1 + mapping of the human body at ultrahigh field (UHF), which can be used to generate homogenous flip angle (FA) distributions in the human body at UHF. METHODS A 3D relative B 1 + mapping sequence with a radial phase-encoding (RPE) k-space trajectory was developed and applied in 11 healthy subjects at 7T. An RPE-based actual flip angle mapping method was applied with a dedicated B 1 + shim setting to calibrate the relative B 1 + maps yielding absolute B 1 + maps of the individual transmit channels. The method was evaluated in a motion phantom and by multidimensional in vivo measurements. Additionally, 3D gradient echo scans with and without static phase-only B 1 + shims were used to qualitatively validate B 1 + shim predictions. RESULTS The phantom validation revealed good agreement for B 1 + maps between dynamic measurement and static reference acquisition. The proposed 3D method was successfully validated in vivo by comparing magnitude and phase distributions with a 2D Cartesian reference. 3D B 1 + maps free from visible motion artifacts were successfully acquired for 11 subjects with body mass indexes ranging from 19 kg/m2 to 34 kg/m2 . 3D respiration-resolved absolute B 1 + maps indicated FA differences between inhalation and exhalation up to 15% for one channel and up to 24% for combined channels for shallow breathing. CONCLUSION The proposed method provides respiration-resolved absolute 3D B 1 + maps of the human body at UHF, which enables the investigation and development of 3D B 1 + shimming and parallel transmission methods to further enhance body imaging at UHF.
Collapse
Affiliation(s)
- Sebastian Dietrich
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Christoph S Aigner
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Christoph Kolbitsch
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Johannes Mayer
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Juliane Ludwig
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
| | - Simon Schmidt
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Tobias Schaeffter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Department of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| | - Sebastian Schmitter
- Physikalisch-Technische Bundesanstalt (PTB), Braunschweig and Berlin, Germany
- Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
- Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA
| |
Collapse
|
93
|
Liorni I, Capstick M, van Wel L, Wiart J, Joseph W, Cardis E, Guxens M, Vermeulen R, Thielens A. EVALUATION OF SPECIFIC ABSORPTION RATE IN THE FAR-FIELD, NEAR-TO-FAR FIELD AND NEAR-FIELD REGIONS FOR INTEGRATIVE RADIOFREQUENCY EXPOSURE ASSESSMENT. RADIATION PROTECTION DOSIMETRY 2020; 190:459-472. [PMID: 32990753 DOI: 10.1093/rpd/ncaa127] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 08/26/2020] [Accepted: 09/10/2020] [Indexed: 06/11/2023]
Abstract
The specific absorption rate (SAR) induced by wireless radiofrequency (RF) systems depends on different parameters. Previously, SAR was mainly assessed under conditions of a single frequency and technology and for a limited number of localized RF sources. The current and emerging mobile systems involve a wider range of usage scenarios and are frequently used simultaneously, leading to combined exposures for which almost no exposure evaluation exists. The aim and novelty of this study is to close this gap of knowledge by developing new methods to rapidly evaluate the SAR induced by RF systems in such scenarios at frequencies from 50 MHz to 5.5 GHz. To this aim, analytical methods for SAR estimation in several usage scenarios were derived through a large-scale numerical study. These include subject-specific characteristics, properties of the RF systems and provide an estimation of the SAR in the whole body, tissues and organs, and different brain regions.
Collapse
Affiliation(s)
- Ilaria Liorni
- Foundation for Research on Information Technologies in Society (IT'IS), Zeughausstrasse 43, 8004 Zürich, Zurich, Switzerland
| | - Myles Capstick
- Foundation for Research on Information Technologies in Society (IT'IS), Zeughausstrasse 43, 8004 Zürich, Zurich, Switzerland
| | - Luuk van Wel
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80178, 3508 TD, Utrecht, the Netherlands
| | - Joe Wiart
- Chaire C2M LTCI, Telecom ParisTech Universitè Paris Saclay, 46 Rue Barrault, 75013 Paris, Paris, France
| | - Wout Joseph
- Department of Information Technology, Ghent University/IMEC, Technologiepark-Zwijnaarde 126, 9052 Ghent, Ghent, Belgium
| | - Elisabeth Cardis
- ISGlobal, Carrer del Rosselló, 132, 08036 Barcelona, Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Plaça de la Mercè, 10-12, 08002 Barcelona, Barcelona, Spain
- CIBER Epidemiología y Salud Pública (CIBERESP), C/ Monforte de Lemos 3-5, 28029 Madrid, Madrid, Spain
| | - Mònica Guxens
- ISGlobal, Carrer del Rosselló, 132, 08036 Barcelona, Barcelona, Spain
- Universitat Pompeu Fabra (UPF), Plaça de la Mercè, 10-12, 08002 Barcelona, Barcelona, Spain
- CIBER Epidemiología y Salud Pública (CIBERESP), C/ Monforte de Lemos 3-5, 28029 Madrid, Madrid, Spain
- Department of Child and Adolescent Psychiatry/Psychology, Erasmus MC, University Medical Centre, Doctor Molewaterplein 40, 3015 GD Rotterdam, Rotterdam, the Netherlands
| | - Roel Vermeulen
- Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80178, 3508 TD, Utrecht, the Netherlands
- Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, Utrecht, the Netherlands
- MRC-PHE Centre for Environment and Health, Department of Epidemiology and Biostatistics, School of Public Health, Imperial College London, Norfolk Place, London W2 1PG, London, UK
| | - Arno Thielens
- Department of Information Technology, Ghent University/IMEC, Technologiepark-Zwijnaarde 126, 9052 Ghent, Ghent, Belgium
| |
Collapse
|
94
|
Fagan AJ, Amrami KK, Welker KM, Frick MA, Felmlee JP, Watson RE. Magnetic Resonance Safety in the 7T Environment. Magn Reson Imaging Clin N Am 2020; 28:573-582. [PMID: 33040997 DOI: 10.1016/j.mric.2020.07.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The arrival of 7T MR imaging into the clinic represents a significant step-change in MR technology. This article describes safety concerns associated with imaging at 7T, including the increased magnetic forces on magnetic objects at 7T and the interaction of the 300 MHz (Larmor) radiofrequency energy with tissue in the body. A dedicated multidisciplinary 7T Safety team should develop safety policies and procedures to address these safety challenges and keep abreast of best practice in the field. The off-label imaging of implanted devices is discussed, and also the need for staff training to deal with complexities of patient handling and image interpretation.
Collapse
Affiliation(s)
- Andrew J Fagan
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA.
| | - Kimberly K Amrami
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Kirk M Welker
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Matthew A Frick
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Joel P Felmlee
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| | - Robert E Watson
- Department of Radiology, Mayo Clinic, 200 First Street Southwest, Rochester, MN 55905, USA
| |
Collapse
|
95
|
Sun X, Wang H, Ristaniemi T. Registration-based Construction of a Whole-body Human Phantom Library for Anthropometric Modeling. ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. IEEE ENGINEERING IN MEDICINE AND BIOLOGY SOCIETY. ANNUAL INTERNATIONAL CONFERENCE 2020; 2020:2396-2399. [PMID: 33018489 DOI: 10.1109/embc44109.2020.9175295] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Various computational human phantoms have been proposed in the past decades, but few of them include delicate anthropometric variations. In this study, we build a whole-body phantom library including 145 anthropometric parameters. This library is constructed by registration-based pipeline, which transfers a standard whole-body anatomy template to an anthropometry-adjustable body shape library (MakeHuman™). Therefore, internal anatomical structures are created for body shapes of different anthropometric parameters. Based on the constructed library, we can generate individualized whole-body phantoms according to given arbitrary anthropometric parameters. Moreover, the proposed phantom library can also be converted to voxel-based and tetrahedron-based model for further personalized simulation. We hope this phantom library will serve as a computational tool in research community.
Collapse
|
96
|
Li M, Li Y, Jin J, Yang Z, Zhang B, Liu Y, Song M, Freakly C, Weber E, Liu F, Jiang T, Crozier S. A dedicated eight-channel receive RF coil array for monkey brain MRI at 9.4 T. NMR IN BIOMEDICINE 2020; 33:e4369. [PMID: 32729642 DOI: 10.1002/nbm.4369] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 06/09/2020] [Accepted: 06/15/2020] [Indexed: 06/11/2023]
Abstract
The neuroimaging of nonhuman primates (NHPs) realised with magnetic resonance imaging (MRI) plays an important role in understanding brain structures and functions, as well as neurodegenerative diseases and pathological disorders. Theoretically, an ultrahigh field MRI (≥7 T) is capable of providing a higher signal-to-noise ratio (SNR) for better resolution; however, the lack of appropriate radiofrequency (RF) coils for 9.4 T monkey MRI undermines the benefits provided by a higher field strength. In particular, the standard volume birdcage coil at 9.4 T generates typical destructive interferences in the periphery of the brain, which reduces the SNR in the neuroscience-focused cortex region. Also, the standard birdcage coil is not capable of performing parallel imaging. Consequently, extended scan durations may cause unnecessary damage due to overlong anaesthesia. In this work, assisted by numerical simulations, an eight-channel receive RF coil array was specially designed and manufactured for imaging NHPs at 9.4 T. The structure and geometry of the proposed receive array was optimised with numerical simulations, so that the SNR enhancement region was particularly focused on monkey brain. Validated with rhesus monkey and cynomolgus monkey brain images acquired from a 9.4 T MRI scanner, the proposed receive array outperformed standard birdcage coil with higher SNR, mean diffusivity and fractional anisotropy values, as well as providing better capability for parallel imaging.
Collapse
Affiliation(s)
- Mingyan Li
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| | - Yu Li
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| | - Jin Jin
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
- Siemens Healthcare Pty. Ltd., Bowen Hills QLD, 4006, Australia
| | - Zhengyi Yang
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing, China
| | - Baogui Zhang
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing, China
| | - Yanyan Liu
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing, China
| | - Ming Song
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing, China
- National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Craig Freakly
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| | - Ewald Weber
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| | - Feng Liu
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| | - Tianzi Jiang
- Brainnetome Center, Institute of Automation, Chinese Academy of Sciences, Beijing, China
- National Laboratory of Pattern Recognition, Institute of Automation, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
- CAS Center for Excellence in Brain Science and Intelligence Technology, Institute of Automation, Chinese Academy of Sciences, Beijing, China
- Key Laboratory for NeuroInformation of Ministry of Education, School of Life Science and Technology, University of Electronic Science and Technology of China, Chengdu, China
- Queensland Brain Institute, University of Queensland, Brisbane, Queensland, Australia
| | - Stuart Crozier
- School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, Queensland, Australia
| |
Collapse
|
97
|
Xia M, Zheng J, Yang R, Song S, Xu J, Liu Q, Kainz W, Long SA, Chen J. Effects of patient orientations, landmark positions, and device positions on the MRI RF-induced heating for modular external fixation devices. Magn Reson Med 2020; 85:1669-1680. [PMID: 32970911 DOI: 10.1002/mrm.28514] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Revised: 08/13/2020] [Accepted: 08/18/2020] [Indexed: 12/17/2022]
Abstract
PURPOSE This paper studies the RF-induced heating for modular external fixation devices applied on the leg regions of the human bodies. Through numerical investigations of RF-induced heating related to different patient orientations, landmark positions, and device positions under 1.5T and 3T MRI systems, simple and practical methods to reduce RF-induced heating are recommended. METHODS Numerical simulations using a full-wave electromagnetic solver based on the finite-difference time-domain method were performed to characterize the effects of patient orientations (head-first/feet-first), landmark positions (the scanning area of the patient), and device positions (device on left or right leg) on the RF-induced heating of the external fixation devices. The G32 coil design and three anatomical human models (Duke model, Ella model, and Fats model) were adopted to model the MRI RF coil and the patients. RESULTS The relative positions of the patient, device, and coil can significantly affect the RF-induced heating. With other conditions remaining the same, changing the device position or patient orientation can lead to a peak 1-g averaged spatial absorption ratio variation of a factor around four. By changing the landmark position and the patient orientation, the RF-induced heating can be reduced from 1323.6 W/kg to 217.5 W/kg for the specific scanning situations studied. CONCLUSION Patient orientations, landmark positions, and device positions influence the RF-induced heating of modular external fixation devices at 1.5 T and 3 T. These features can be used to reduce the RF-induced heating during MRI simply and practically.
Collapse
Affiliation(s)
- Meiqi Xia
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Jianfeng Zheng
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Rui Yang
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Shuo Song
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Jian Xu
- UIH America Inc, Houston, Texas, USA
| | - Qi Liu
- UIH America Inc, Houston, Texas, USA
| | - Wolfgang Kainz
- Center for Devices and Radiological Health (CDRH), US Food and Drug Administration (FDA), Silver Spring, Maryland, USA
| | - Stuart A Long
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| | - Ji Chen
- Department of Electrical and Computer Engineering, University of Houston, Houston, Texas, USA
| |
Collapse
|
98
|
VilasBoas-Ribeiro I, van Rhoon GC, Drizdal T, Franckena M, Paulides MM. Impact of Number of Segmented Tissues on SAR Prediction Accuracy in Deep Pelvic Hyperthermia Treatment Planning. Cancers (Basel) 2020; 12:cancers12092646. [PMID: 32947939 PMCID: PMC7563220 DOI: 10.3390/cancers12092646] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2020] [Revised: 09/10/2020] [Accepted: 09/14/2020] [Indexed: 11/16/2022] Open
Abstract
Simple Summary Hyperthermia treatment planning is the process of optimizing treatment quality using pre-treatment simulations. Although it has become a powerful tool, prediction accuracy is strongly dependent on the patient model. For deep hyperthermia in the pelvis, it is common that only four tissue categories are discriminated (bone, fat, muscle-like, and tumor). For the head and neck region, more tissues have been shown to be required for good prediction accuracy. Delineating is a labor-intensive and difficult process. Hence, it is important to find the optimum between accuracy and labor, but for deep pelvic hyperthermia, there are no published studies showing the impact of the number of tissues. We studied the trade-off between the segmentation detail needed and segmentation feasibility. Our findings indicate that including high water content tissues can impact simulation accuracy. Although our results, in general, underline the suitability of our current clinical protocol, they help to prioritize improvements for specific cases. Abstract In hyperthermia, the general opinion is that pre-treatment optimization of treatment settings requires a patient-specific model. For deep pelvic hyperthermia treatment planning (HTP), tissue models comprising four tissue categories are currently discriminated. For head and neck HTP, we found that more tissues are required for increasing accuracy. In this work, we evaluated the impact of the number of segmented tissues on the predicted specific absorption rate (SAR) for the pelvic region. Highly detailed anatomical models of five healthy volunteers were selected from a virtual database. For each model, seven lists with varying levels of segmentation detail were defined and used as an input for a modeling study. SAR changes were quantified using the change in target-to-hotspot-quotient and maximum SAR relative differences, with respect to the most detailed patient model. The main finding of this study was that the inclusion of high water content tissues in the segmentation may result in a clinically relevant impact on the SAR distribution and on the predicted hyperthermia treatment quality when considering our pre-established thresholds. In general, our results underline the current clinical segmentation protocol and help to prioritize any improvements.
Collapse
Affiliation(s)
- Iva VilasBoas-Ribeiro
- Department of Radiation Oncology, Erasmus MC Cancer Institute, 3015 GD Rotterdam, The Netherlands; (G.C.v.R.); (M.F.); (M.M.P.)
- Correspondence:
| | - Gerard C. van Rhoon
- Department of Radiation Oncology, Erasmus MC Cancer Institute, 3015 GD Rotterdam, The Netherlands; (G.C.v.R.); (M.F.); (M.M.P.)
- Department of Radiation Science and Technology, Faculty of Applied Sciences, Delft University of Technology, 2629 JB Delft, The Netherlands
| | - Tomas Drizdal
- Department of Biomedical Technology, Czech Technical University in Prague, nam. Sitna 3105, 272 01 Kladno, Czech Republic;
| | - Martine Franckena
- Department of Radiation Oncology, Erasmus MC Cancer Institute, 3015 GD Rotterdam, The Netherlands; (G.C.v.R.); (M.F.); (M.M.P.)
| | - Margarethus M. Paulides
- Department of Radiation Oncology, Erasmus MC Cancer Institute, 3015 GD Rotterdam, The Netherlands; (G.C.v.R.); (M.F.); (M.M.P.)
- Electromagnetics for Care & Cure (EM-4C&C) Laboratory, Center for Care and Cure Technologies Eindhoven (C3Te), Department of Electrical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
| |
Collapse
|
99
|
Performance of parallel FDTD method for shared- and distributed-memory architectures: Application tobioelectromagnetics. PLoS One 2020; 15:e0238115. [PMID: 32915812 PMCID: PMC7485784 DOI: 10.1371/journal.pone.0238115] [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: 01/27/2020] [Accepted: 08/10/2020] [Indexed: 11/19/2022] Open
Abstract
This work provides an in-depth computational performance study of the parallel finite-difference time-domain (FDTD) method. The parallelization is done at various levels including: shared- (OpenMP) and distributed- (MPI) memory paradigms and vectorization on three different architectures: Intel's Knights Landing, Skylake and ARM's Cavium ThunderX2. This study contributes to prove, in a systematic manner, the well-established claim within the Computational Electromagnetic community, that the main factor limiting FDTD performance, in realistic problems, is the memory bandwidth. Consequently a memory bandwidth threshold can be assessed depending on the problem size in order to attain optimal performance. Finally, the results of this study have been used to optimize the workload balancing of simulation of a bioelectromagnetic problem consisting in the exposure of a human model to a reverberation chamber-like environment.
Collapse
|
100
|
Tsanidis G, Samaras T. Numerical calculation of the radiofrequency transfer function of cochlear implants for assessing deposited power in MRI. Phys Med Biol 2020; 65:175005. [PMID: 32580168 DOI: 10.1088/1361-6560/ab9fc7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The medical imaging of patients with a cochlear implant inside a Magnetic Resonance Imaging (MRI) scanner carries the risk of power deposition in the tissues at the tip of the implant lead, which may result in their heating. In order to assess this risk, ISO/TS 10 974 (2018) describes a methodology (Tier 3 approach) whereby a radiofrequency electrical model for the implant lead in the form of a transfer function is constructed. The construction of the transfer function takes place by assuming that a homogenous medium surrounds the implant, whereas, in reality, implants can traverse various tissues of different electrical properties. The results show that the use of a High Permittivity Medium (HPM) overestimates the Tier 3 calculated deposited power by almost 6 dB, whereas a Low Permittivity Medium (LPM) underestimates it by 9 dB, compared to the in vivo power deposition in three virtual human models, obtained following the Tier 4 approach of ISO/TS 10 974(2018). Since the Tier 3 approach requires less computational resources compared to Tier 4, we suggest its modification with the use of two media (mixed media approach), where implant is immersed. By carefully choosing the media electrical properties, it is possible to calculate power deposition values at the lead tip that differ less than 1 dB from the in vivo ones.
Collapse
Affiliation(s)
- George Tsanidis
- Department of Physics, Aristotle University of Thessaloniki, Thessaloniki, Greece. Thessaloniki Software Solutions (THESS) S.A., Technopolis ICT Business Park, Thessaloniki, Greece
| | | |
Collapse
|