Pub Date : 2023-03-07DOI: 10.1109/JERM.2023.3247904
Peter Serano;Johnathan W. Adams;Louis Chen;Ara Nazarian;Reinhold Ludwig;Sergey Makaroff
On-body antennas for use in microwave imaging (MI) systems can direct energy around the body instead of through the body, thus degrading the overall signal-to-noise ratio (SNR) of the system. This work introduces and quantifies the usage of modern metal-backed RF absorbing foam in conjunction with on-body antennas to dampen energy flowing around the body, using both simulations and experiments. A head imaging system is demonstrated herein but the principle can be applied to any part of the body including the torso or extremities. A computational model was simulated numerically using Ansys HFSS. A physical prototype in the form of a helmet with embedded antennas was built to compare simulations with measured data. Simulations and measurements demonstrate that usage of such metal-backed RF-absorbing foams can significantly reduce around-body coupling from Transmit (Tx) and Receive (Rx) antennas by approximately 10 dB. Thus, the overall SNR of the MI system can be substantially improved using this low-cost and affordable method.
{"title":"Reducing Non-Through Body Energy Transfer in Microwave Imaging Systems","authors":"Peter Serano;Johnathan W. Adams;Louis Chen;Ara Nazarian;Reinhold Ludwig;Sergey Makaroff","doi":"10.1109/JERM.2023.3247904","DOIUrl":"10.1109/JERM.2023.3247904","url":null,"abstract":"On-body antennas for use in microwave imaging (MI) systems can direct energy around the body instead of through the body, thus degrading the overall signal-to-noise ratio (SNR) of the system. This work introduces and quantifies the usage of modern metal-backed RF absorbing foam in conjunction with on-body antennas to dampen energy flowing around the body, using both simulations and experiments. A head imaging system is demonstrated herein but the principle can be applied to any part of the body including the torso or extremities. A computational model was simulated numerically using Ansys HFSS. A physical prototype in the form of a helmet with embedded antennas was built to compare simulations with measured data. Simulations and measurements demonstrate that usage of such metal-backed RF-absorbing foams can significantly reduce around-body coupling from Transmit (Tx) and Receive (Rx) antennas by approximately 10 dB. Thus, the overall SNR of the MI system can be substantially improved using this low-cost and affordable method.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 2","pages":"187-192"},"PeriodicalIF":3.2,"publicationDate":"2023-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=10061855","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41239316","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-03DOI: 10.1109/JERM.2023.3247959
Johnathan W. Adams;Louis Chen;Peter Serano;Ara Nazarian;Reinhold Ludwig;Sergey N. Makaroff
An on-body antenna, comprised of two closely-spaced antiphase patch elements, for microwave imaging may provide enhanced signal penetration into the tissue. By further integrating a 180-degree on-chip power splitter with the dual antiphase patch antenna element, a low-profile miniaturized antenna, integrated into a single 18.5 mm × 10 mm × 1.6 mm circuit board assembly, is designed and evaluated both numerically and experimentally. This is the smallest on-body antenna known to the authors for the given frequency band. This linearly polarized antenna may potentially serve as a building block of a dense antenna array for prospective high-resolution microwave imaging. A 2.4 GHz band was chosen as the design target. The final antenna size was a compromise between the miniaturization, the SNR (Signal-to-Noise Ratio), and the targeted antenna bandwidth (2.3–2.5 GHz). The effect of surface waves (the secondary radiating components) was also factored in the design consideration, while maximizing the detected signals’ SNR.
{"title":"Miniaturized Dual Antiphase Patch Antenna Radiating Into the Human Body at 2.4 GHz","authors":"Johnathan W. Adams;Louis Chen;Peter Serano;Ara Nazarian;Reinhold Ludwig;Sergey N. Makaroff","doi":"10.1109/JERM.2023.3247959","DOIUrl":"https://doi.org/10.1109/JERM.2023.3247959","url":null,"abstract":"An on-body antenna, comprised of two closely-spaced antiphase patch elements, for microwave imaging may provide enhanced signal penetration into the tissue. By further integrating a 180-degree on-chip power splitter with the dual antiphase patch antenna element, a low-profile miniaturized antenna, integrated into a single 18.5 mm × 10 mm × 1.6 mm circuit board assembly, is designed and evaluated both numerically and experimentally. This is the smallest on-body antenna known to the authors for the given frequency band. This linearly polarized antenna may potentially serve as a building block of a dense antenna array for prospective high-resolution microwave imaging. A 2.4 GHz band was chosen as the design target. The final antenna size was a compromise between the miniaturization, the SNR (Signal-to-Noise Ratio), and the targeted antenna bandwidth (2.3–2.5 GHz). The effect of surface waves (the secondary radiating components) was also factored in the design consideration, while maximizing the detected signals’ SNR.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 2","pages":"182-186"},"PeriodicalIF":3.2,"publicationDate":"2023-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50238622","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-02DOI: 10.1109/JERM.2023.3268553
Audrey L. Evans;Ruixi L. Liu;Chu Ma;Susan C. Hagness
The temperature dependence of microwave-induced thermoacoustic signals generated in tissue may be exploited to monitor microwave ablation in real-time. We present an experimental study investigating the evolution of microwave-induced thermoacoustic signals that are generated within an ablation zone during microwave ablation in bovine liver tissue. An X-band interstitial coaxial ablation antenna is used to simultaneously heat liver tissue to temperatures up to 90 $^{circ }$ C and excite thermoacoustic signals via the absorption of pulsed microwave energy. Thermoacoustic signals are detected using a single-element ultrasound transducer located at the surface of the tissue. Both fresh and boiled liver tissue samples are used in experiments to decouple the influence of temperature and tissue coagulation on thermoacoustic signal characteristics. We identify two thermoacoustic signal characteristics of interest: arrival time of the pulse at the ultrasound receiver and the energy in the pulse. We find that the time difference of arrival over the course of microwave ablation grows in magnitude due to temperature-dependent speed of sound and tissue shrinkage. Thermoacoustic signal energy generally increases throughout microwave ablation, implying an increasing temperature-dependent thermal expansion coefficient of liver tissue. Of the two characteristics, time difference of arrival shows the most promise as a trackable feature for monitoring microwave ablation in real time.
{"title":"The Evolution of Microwave-Induced Thermoacoustic Signals Generated During Pulsed Microwave Ablation in Bovine Liver","authors":"Audrey L. Evans;Ruixi L. Liu;Chu Ma;Susan C. Hagness","doi":"10.1109/JERM.2023.3268553","DOIUrl":"https://doi.org/10.1109/JERM.2023.3268553","url":null,"abstract":"The temperature dependence of microwave-induced thermoacoustic signals generated in tissue may be exploited to monitor microwave ablation in real-time. We present an experimental study investigating the evolution of microwave-induced thermoacoustic signals that are generated within an ablation zone during microwave ablation in bovine liver tissue. An X-band interstitial coaxial ablation antenna is used to simultaneously heat liver tissue to temperatures up to 90 \u0000<inline-formula><tex-math>$^{circ }$</tex-math></inline-formula>\u0000C and excite thermoacoustic signals via the absorption of pulsed microwave energy. Thermoacoustic signals are detected using a single-element ultrasound transducer located at the surface of the tissue. Both fresh and boiled liver tissue samples are used in experiments to decouple the influence of temperature and tissue coagulation on thermoacoustic signal characteristics. We identify two thermoacoustic signal characteristics of interest: arrival time of the pulse at the ultrasound receiver and the energy in the pulse. We find that the time difference of arrival over the course of microwave ablation grows in magnitude due to temperature-dependent speed of sound and tissue shrinkage. Thermoacoustic signal energy generally increases throughout microwave ablation, implying an increasing temperature-dependent thermal expansion coefficient of liver tissue. Of the two characteristics, time difference of arrival shows the most promise as a trackable feature for monitoring microwave ablation in real time.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 3","pages":"273-280"},"PeriodicalIF":3.2,"publicationDate":"2023-03-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50291934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-01DOI: 10.1109/JERM.2023.3267042
Tom P. G. van Nunen;Rob M. C. Mestrom;Hubregt J. Visser
In this article, we propose a strategy for the design of a wireless power transfer system consisting of a class-E inverter, a half-bridge class-DE rectifier, and two coupled coils. The system is optimized for maximum power transfer efficiency. The design is validated via a case study, for which a wireless power transfer link to a neuroprosthesis was designed. After circuit simulations, a prototype was realized and measured. There is a good agreement between the calculated, simulated and measured voltages and currents. The prototype delivers ${text {80}}$ mW, ${text {7}}$ V to a biomedical implant at ${text {6.78}}$ MHz, the transfer efficiency is ${text {52}}$ to 68%, depending on the alignment. The end-to-end efficiency, with the controller and gate driver also taken into account, is ${text {39}}$ to 57%. Electromagnetic and thermal simulations were performed to verify compliance with relevant safety regulations on specific absorption rate (SAR) levels, magnetic field strength, and heat generation in the implant, for separation distances between the coils of ${text {8}}$ to ${text {15}}$ mm, and transverse misalignment from ${text {0}}$ to $text {15}$ mm.
{"title":"Wireless Power Transfer to Biomedical Implants Using a Class-E Inverter and a Class-DE Rectifier","authors":"Tom P. G. van Nunen;Rob M. C. Mestrom;Hubregt J. Visser","doi":"10.1109/JERM.2023.3267042","DOIUrl":"https://doi.org/10.1109/JERM.2023.3267042","url":null,"abstract":"In this article, we propose a strategy for the design of a wireless power transfer system consisting of a class-E inverter, a half-bridge class-DE rectifier, and two coupled coils. The system is optimized for maximum power transfer efficiency. The design is validated via a case study, for which a wireless power transfer link to a neuroprosthesis was designed. After circuit simulations, a prototype was realized and measured. There is a good agreement between the calculated, simulated and measured voltages and currents. The prototype delivers \u0000<inline-formula><tex-math>${text {80}}$</tex-math></inline-formula>\u0000 mW, \u0000<inline-formula><tex-math>${text {7}}$</tex-math></inline-formula>\u0000 V to a biomedical implant at \u0000<inline-formula><tex-math>${text {6.78}}$</tex-math></inline-formula>\u0000 MHz, the transfer efficiency is \u0000<inline-formula><tex-math>${text {52}}$</tex-math></inline-formula>\u0000 to 68%, depending on the alignment. The end-to-end efficiency, with the controller and gate driver also taken into account, is \u0000<inline-formula><tex-math>${text {39}}$</tex-math></inline-formula>\u0000 to 57%. Electromagnetic and thermal simulations were performed to verify compliance with relevant safety regulations on specific absorption rate (SAR) levels, magnetic field strength, and heat generation in the implant, for separation distances between the coils of \u0000<inline-formula><tex-math>${text {8}}$</tex-math></inline-formula>\u0000 to \u0000<inline-formula><tex-math>${text {15}}$</tex-math></inline-formula>\u0000 mm, and transverse misalignment from \u0000<inline-formula><tex-math>${text {0}}$</tex-math></inline-formula>\u0000 to \u0000<inline-formula><tex-math>$text {15}$</tex-math></inline-formula>\u0000 mm.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 3","pages":"202-209"},"PeriodicalIF":3.2,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10226431/10113711.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50291927","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-01DOI: 10.1109/JERM.2023.3268555
Marta Bonato;Emma Chiaramello;Marta Parazzini;Peter Gajšek;Paolo Ravazzani
Extremely Low Frequency Electric (ELF-EF) and Magnetic Field (ELF-MF) exposure is caused by different types of sources, from those related to the production, transmission, and distribution of electric currents, to technologies of common use, such as domestic appliances or electric transportation. Establishing the levels of exposure for general public is a fundamental step in the health risk management process but could be challenging due to differences in the approaches used in different studies. The goal of this study is to present an overview of the last years research efforts (from 2015 to nowadays) about ELF-EF and MF exposure in everyday environments, considering different sources and different approaches used to assess the exposure. All ELF-EMF exposure levels were found to be below the ICNIRP guidelines for general public exposure. The higher MF levels were measured in apartments very close to built-in power transformers. Household electrical devices showed high levels of MF exposure in their proximity, but the duration of such exposure is extremely limited.
{"title":"Extremely Low Frequency Electric and Magnetic Fields Exposure: Survey of Recent Findings","authors":"Marta Bonato;Emma Chiaramello;Marta Parazzini;Peter Gajšek;Paolo Ravazzani","doi":"10.1109/JERM.2023.3268555","DOIUrl":"https://doi.org/10.1109/JERM.2023.3268555","url":null,"abstract":"Extremely Low Frequency Electric (ELF-EF) and Magnetic Field (ELF-MF) exposure is caused by different types of sources, from those related to the production, transmission, and distribution of electric currents, to technologies of common use, such as domestic appliances or electric transportation. Establishing the levels of exposure for general public is a fundamental step in the health risk management process but could be challenging due to differences in the approaches used in different studies. The goal of this study is to present an overview of the last years research efforts (from 2015 to nowadays) about ELF-EF and MF exposure in everyday environments, considering different sources and different approaches used to assess the exposure. All ELF-EMF exposure levels were found to be below the ICNIRP guidelines for general public exposure. The higher MF levels were measured in apartments very close to built-in power transformers. Household electrical devices showed high levels of MF exposure in their proximity, but the duration of such exposure is extremely limited.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 3","pages":"216-228"},"PeriodicalIF":3.2,"publicationDate":"2023-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10226431/10113779.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50291937","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-28DOI: 10.1109/JERM.2023.3246722
Kyle A. Thackston;Mara D. Casebeer;Dimitri D. Deheyn;Andreas W. Götz;Daniel F. Sievenpiper
There is a great deal of interest in interactions between biomolecules and high frequency electromagnetic (EM) fields. To investigate these interactions, a variety of simulation methods are available. For small length and time scales (approximately $< $$1 ,mathrm{mu }mathrm{s}$ and $100 ,mathrm{n}mathrm{m}$ ), All-Atom Molecular Dynamics simulates every atom in the system. This captures the relevant physics to a high degree of accuracy. Phenomena such as electric field screening by counter-ions are emergent properties from the collective interactions of these atoms. For larger systems on longer time scales, however, this method is too computationally expensive. To reduce complexity, other simulation techniques such as Brownian Dynamics treat the solvent as a continuum, instead of explicitly. One typical assumption is that electric field interactions are electrostatic and subjected to Debye screening. Once charges start moving at high frequencies and velocities, however, charges are able to outrun the counter-ion cloud and this assumption breaks down. We propose a method of removing the electrostatic assumption without explicitly modeling the solvent or imposing a grid on the simulation. We demonstrate the charged wake can be modeled using a finite trail of charges. Interactions can be computed using electrostatic expressions only, but still capture electrodynamics.
{"title":"Modeling Electrodynamic Interactions in Brownian Dynamics Simulations","authors":"Kyle A. Thackston;Mara D. Casebeer;Dimitri D. Deheyn;Andreas W. Götz;Daniel F. Sievenpiper","doi":"10.1109/JERM.2023.3246722","DOIUrl":"https://doi.org/10.1109/JERM.2023.3246722","url":null,"abstract":"There is a great deal of interest in interactions between biomolecules and high frequency electromagnetic (EM) fields. To investigate these interactions, a variety of simulation methods are available. For small length and time scales (approximately \u0000<inline-formula><tex-math>$< $</tex-math></inline-formula>\u0000 \u0000<inline-formula><tex-math>$1 ,mathrm{mu }mathrm{s}$</tex-math></inline-formula>\u0000 and \u0000<inline-formula><tex-math>$100 ,mathrm{n}mathrm{m}$</tex-math></inline-formula>\u0000), All-Atom Molecular Dynamics simulates every atom in the system. This captures the relevant physics to a high degree of accuracy. Phenomena such as electric field screening by counter-ions are emergent properties from the collective interactions of these atoms. For larger systems on longer time scales, however, this method is too computationally expensive. To reduce complexity, other simulation techniques such as Brownian Dynamics treat the solvent as a continuum, instead of explicitly. One typical assumption is that electric field interactions are electrostatic and subjected to Debye screening. Once charges start moving at high frequencies and velocities, however, charges are able to outrun the counter-ion cloud and this assumption breaks down. We propose a method of removing the electrostatic assumption without explicitly modeling the solvent or imposing a grid on the simulation. We demonstrate the charged wake can be modeled using a finite trail of charges. Interactions can be computed using electrostatic expressions only, but still capture electrodynamics.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 2","pages":"176-181"},"PeriodicalIF":3.2,"publicationDate":"2023-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50238621","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-17DOI: 10.1109/JERM.2023.3243510
{"title":"IEEE Journal of Electromagnetics, RF, and Microwaves in Medicine and Biology About this Journal","authors":"","doi":"10.1109/JERM.2023.3243510","DOIUrl":"https://doi.org/10.1109/JERM.2023.3243510","url":null,"abstract":"","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 1","pages":"C3-C3"},"PeriodicalIF":3.2,"publicationDate":"2023-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10048702/10048713.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50411262","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-17DOI: 10.1109/JERM.2023.3243506
{"title":"IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology Publication Information","authors":"","doi":"10.1109/JERM.2023.3243506","DOIUrl":"https://doi.org/10.1109/JERM.2023.3243506","url":null,"abstract":"","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 1","pages":"C2-C2"},"PeriodicalIF":3.2,"publicationDate":"2023-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10048702/10048709.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50411259","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-17DOI: 10.1109/JERM.2023.3235264
{"title":"2022 List of Reviewers","authors":"","doi":"10.1109/JERM.2023.3235264","DOIUrl":"https://doi.org/10.1109/JERM.2023.3235264","url":null,"abstract":"","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 1","pages":"99-100"},"PeriodicalIF":3.2,"publicationDate":"2023-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10048702/10048710.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50411261","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-14DOI: 10.1109/JERM.2023.3236153
Jessica A. Martinez;Alessandro Arduino;Oriano Bottauscio;Luca Zilberti
The specific absorption rate (SAR) estimates the amount of power absorbed by the tissue and is determined by the electrical conductivity and the E-field. Conductivity can be estimated using Electric Properties Tomography (EPT) but only the E-field component associated with $B_{1}^+$ can be deduced from $B_{1}$ -mapping. Herein, a correction factor was calculated to compensate for the differences between the actual SAR and the one obtained with $B_{1}^+$ . Numerical simulations were performed for 27 head models at $128 ,mathrm{M}mathrm{Hz}$ . Ground-truth local-SAR and 10g-SAR (SAR GT ) were computed using the exact electrical conductivity and the E-field. Estimated local-SAR and 10g-SAR (SAR EST ) were computed using the electrical conductivity obtained with a convection-reaction EPT and the E-field obtained from $B_{1}^+$ . Correction factors (CFs) were estimated for gray matter, white matter, and cerebrospinal fluid (CSF). A comparison was performed for different levels of signal-to-noise ratios (SNR). Local-SAR/10g-SAR CF was 3.08 $pm$ 0/06 / 2.11 $pm$ 0.04 for gray matter, 1.79 $pm$ 0/05 / 2.06 $pm$ 0.04 for white matter, and 2.59 $pm$ 0/05 / 1.95 $pm$ 0.03 for CSF. SAR EST without CF were underestimated (ratio across [ $infty$ - 25] SNRs: 0.52 $pm$ 0.02 for local-SAR; 0.55 $pm$ 0.01 for 10g-SAR). After correction, SAR EST was equivalent to SAR GT (ratio across [ $infty$ - 25] SNRs: 0.97 $pm$ 0.02 for local-SAR; 1.06 $pm$ 0.01 for 10g-SAR). SAR maps based on $B_{1}^+$ can be corrected with a correction factor to compensate for potential differences between the actual SAR and the SAR calculated with the E-field derived from $B_{1}^+$ .
{"title":"Evaluation and Correction of $B_{1}^+$-Based Brain Subject-Specific SAR Maps Using Electrical Properties Tomography","authors":"Jessica A. Martinez;Alessandro Arduino;Oriano Bottauscio;Luca Zilberti","doi":"10.1109/JERM.2023.3236153","DOIUrl":"https://doi.org/10.1109/JERM.2023.3236153","url":null,"abstract":"The specific absorption rate (SAR) estimates the amount of power absorbed by the tissue and is determined by the electrical conductivity and the E-field. Conductivity can be estimated using Electric Properties Tomography (EPT) but only the E-field component associated with \u0000<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\u0000 can be deduced from \u0000<inline-formula><tex-math>$B_{1}$</tex-math></inline-formula>\u0000-mapping. Herein, a correction factor was calculated to compensate for the differences between the actual SAR and the one obtained with \u0000<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\u0000. Numerical simulations were performed for 27 head models at \u0000<inline-formula><tex-math>$128 ,mathrm{M}mathrm{Hz}$</tex-math></inline-formula>\u0000. Ground-truth local-SAR and 10g-SAR (SAR\u0000<sub>GT</sub>\u0000) were computed using the exact electrical conductivity and the E-field. Estimated local-SAR and 10g-SAR (SAR\u0000<sub>EST</sub>\u0000) were computed using the electrical conductivity obtained with a convection-reaction EPT and the E-field obtained from \u0000<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\u0000. Correction factors (CFs) were estimated for gray matter, white matter, and cerebrospinal fluid (CSF). A comparison was performed for different levels of signal-to-noise ratios (SNR). Local-SAR/10g-SAR CF was 3.08 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0/06 / 2.11 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.04 for gray matter, 1.79 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0/05 / 2.06 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.04 for white matter, and 2.59 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0/05 / 1.95 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.03 for CSF. SAR\u0000<sub>EST</sub>\u0000 without CF were underestimated (ratio across [\u0000<inline-formula><tex-math>$infty$</tex-math></inline-formula>\u0000 - 25] SNRs: 0.52 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.02 for local-SAR; 0.55 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.01 for 10g-SAR). After correction, SAR\u0000<sub>EST</sub>\u0000 was equivalent to SAR\u0000<sub>GT</sub>\u0000 (ratio across [\u0000<inline-formula><tex-math>$infty$</tex-math></inline-formula>\u0000 - 25] SNRs: 0.97 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.02 for local-SAR; 1.06 \u0000<inline-formula><tex-math>$pm$</tex-math></inline-formula>\u0000 0.01 for 10g-SAR). SAR maps based on \u0000<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\u0000 can be corrected with a correction factor to compensate for potential differences between the actual SAR and the SAR calculated with the E-field derived from \u0000<inline-formula><tex-math>$B_{1}^+$</tex-math></inline-formula>\u0000.","PeriodicalId":29955,"journal":{"name":"IEEE Journal of Electromagnetics RF and Microwaves in Medicine and Biology","volume":"7 2","pages":"168-175"},"PeriodicalIF":3.2,"publicationDate":"2023-02-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/iel7/7397573/10138047/10044569.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"50238039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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