SAR Distribution Research Articles

Analysis of SAR mitigation implementing millimeter wave antenna with FSS-based absorber for 5 G application

In this article, an FSS-based absorber has been developed and utilized to mitigate the specific absorption rate of a millimeter-wave antenna loaded with an inter-digital capacitor (IDC) for 5 G applications. SAR mitigation of millimeter-wave antennas is one of the aspects to be considered for next-generation applications. The addition of a triple-band absorber operating at 28, 60, and 73 GHz reduces the SAR value by blocking radiation on the antenna's backside. This approach lowered the value of the SAR by 75 % and more through the targeted operating bands, diminished significantly the SAR distribution, and increased the antenna gain. In accordance with the Federal Communications Commission and International Commission on Non-Ionizing Radiation Protection (ICNIRP) regulations, a decrease in SAR values signify a decrement in radiation absorption by human tissue, thereby lowering the likelihood of health risks from electromagnetic radiation. Rogers RT-Duroid 5880 serves as the antenna's substrate, while epoxy resin fiber (FR-4) is used for the absorber. The investigation's findings in the constructed antenna sample with the incorporated absorber demonstrate that the modeled and observed results correspond well, demonstrating the viability and effectiveness of the unique design in SAR mitigation in millimeter wave bands.

Study upon the influence of mobile phone protective case on SAR distribution

Abstract The article presents a series of simulations performed with CST Studio software, using the Hugo male model, a member of CST Voxel Family. These simulations aim to study the effect that the conductivity (thermal and electrical) of the phone protective case might have on the SAR distribution. In the first part, details are presented on how to understand and use the SAR parameter, on how CST Studio simulates it, complementary with the method of delivery of the obtained data. All 6 communication ports of the available phone model have been tested, 4 of them intended for 2G, 2G+, 3G, 4G mobile phone technologies, the other 2 being dedicated to the two Wi-Fi standards (2.4 and 5 GHz). The phone has been placed in the left breast pocket (near heart). The SAR values have been compared for three different cases: silicone protective case without conductive foil, with 0.5 mm Aluminum conductive foil, placed between the phone and the case and with foil of the same thickness, but made of Copper. Conclusions have been drawn regarding the SAR reduction percentages as a result of the use of conductive foils. A recommendation regarding an efficient and accessible solution for designing and making phone protective cases has been issued.

A Mathematical Analysis of Clustering-Free Local SAR Compression Algorithms for MRI Safety in Parallel Transmission.

Parallel transmission (pTX) is a versatile solution to enable UHF MRI of the human body, where radiofrequency (RF) field inhomogeneity appears very challenging. Today, state of the art monitoring of the local SAR in pTX consists in evaluating the RF power deposition on specific SAR matrices called Virtual Observation Points (VOPs). It essentially relies on accurate electromagnetic simulations able to return the local SAR distribution inside the body in response to any applied pTX RF waveform. In order to reduce the number of SAR matrices to a value compatible with real time SAR monitoring ( << 103) , a VOP set is obtained by partitioning the SAR model into clusters, and associating a so- called dominant SAR matrix to every cluster. More recently, a clustering-free compression method was proposed, allowing for a significant reduction in the number of SAR matrices. The concept and derivation however assumed static RF shims and their extension to dynamic pTX is not straightforward, thereby casting doubt on the strict validity of the compression approach for these more complicated RF waveforms. In this work, we provide the mathematical framework to tackle this problem and find a rigorous justification of this criterion in the light of convex optimization theory. Our analysis led us to a variant of the clustering-free compression approach exploiting convex optimization. This new compression algorithm offers computational gains for large SAR models and for high-channel count pTX RF coils.

Study on the distribution of SAR and temperature in human brain during radio-frequency cosmetic treatment

Study on the distribution of SAR and temperature in human brain during radio-frequency cosmetic treatment

SAR Analysis Using Various Substrates of Microstrip Antenna for Breast Cancer Hyperthermia Treatment

Hyperthermia is an alternative technique used to treat breast cancer using high heat, around 41°C to 45°C, to denature cancer tissue into necrotic tissue. It can work independently or in adjuvant with other conventional methods. The design of an antenna with a suitable substrate is essential for the applicator to transmit maximal heat to the intended area and distribute the heat uniformly on the treated tissues. Therefore, the inset feed microstrip antenna is design with five different substrates, simulated, analyzed, and their performance is compared to get the best substrate. The substrates used include Rogers Duroid RT5880, Rogers RO4003, FR4, Alumina and Rogers RO3010. SEMCAD X 14.8.4 software is used to design, simulate and generate SAR. RT5880 and RO4003 show better SAR distribution and focus position distance (FPD), which can be further examined for future research. 2450 MHz, 915 MHz and 434 MHz frequencies are compared to find the most suitable frequency to apply with the applicator. A 915 MHz frequency shows better performance which can penetrate more toward the cancerous areas. However, there are several deficiencies such as difficulty in controlling FPD, wide unwanted hotspot and massive skin burn problem, that needs to be improved to provide less adverse health effects due to the execution of hyperthermia treatment. The selection of suitable substrates can help reduce the deficiencies and improve the effectiveness of the hyperthermia technique. The estimated period is within 2 hours to 3.6 hours to achieve sufficient heating to destroy the cancerous cells.

Thermal measurements of a muscle-mimicking phantom during ultra-high field magnetic resonance imaging

Abstract At ultra-high field MRI (Bo&gt;7T) it is crucial to predict and control the patient safety. Commonly patient safety is controlled by the power deposited in the tissue (specific absorption rate - SAR). However, temperature distributions do not always correlate directly with SAR distributions, which makes temperature control also a crucial parameter to guarantee patient safety. In this work, temperature changes were accessed by MR thermometry, specifically by the proton resonance frequency shift technique (PRF). A phantom mimicking muscle tissue was used to evaluate the temperature rise caused by the radiofrequency (RF) absorption during 7T MRI, applied through a commercial birdcage head coil. A pulse-sequence protocol was implemented for both, the generation of temperature increase and the MR thermometry. To control the temperature, a digital thermometer was used, and oil tubes were utilized to dismiss the drift effects for PRF. Measurements of the phantom’s dielectric characteristics, i.e. conductivity and permittivity, were in good agreement with the literature values for muscle. Spatio-temporal evaluations showed a temperature increase in time via RF exposure and the feasibility of measuring temperature maps using the PRF shift method. The accuracy of the PRF shift method increased when the drift effects were quantified and dismissed, indicating a PRF reading accuracy differing less than 0.5 °C from the thermometer. Results also validate our heating and temperature imaging protocol. This study is a valuable contribution to the evaluation of heating effects caused by RF absorption and demonstrates potential impact on future thermal investigations, which may use different heating sources, as well validate thermal simulations.

Design of Ultra-Wideband Phased Array Applicator for Breast Cancer Hyperthermia Therapy.

Focused microwave-hyperthermia therapy has recently emerged as a key technology in the treatment of breast cancer due to non-invasive treatment. An applicator of a three-ring phased array consisting of ultra-wideband (UWB) microstrip antennas was designed for breast cancer therapy and operates at 0.915 GHz and 2.45 GHz. The proposed antenna has an ultra-wideband from 0.7 GHz to 5.5 GHz with resonant frequencies of 0.915 GHz and 2.45 GHz and dimensions of 15 × 43.5 × 1.575 mm3. The number of each ring was chosen to be 12 based on the SAR distribution and the performance indicators of tumor off-center focusing results for four different numbers of single-ring arrays. The homogeneous breast model is applied to a three-ring phased array consisting of 36 elements for focused simulation, and 1 cm3 and 2 cm3 tumors are placed in three different locations in the breast. The simulation results show that the proposed phased array has good performance and the capability to raise the temperature of different volumes of breast cancer above 42.5 °C after choosing a suitable operating frequency. The proposed applicator allows for precise treatment of tumors by selecting the appropriate operating frequency based on the size of the malignant tumor.

NUMERICAL SIMULATIONS OF A FLAT PHANTOM IN THE NEAR-FIELD OF SYMMETRIC DIPOLE ANTENNA

The paper presents a numerical electromagnetic simulations of SAR limited to human tissues based on FDTD algorithm using Sim4Life platform. Flat-bottomed dielectric vessel (flat phantom) and half-wave symmetric dipole antenna were modeled. Simulations were done for the frequencies 0.9 GHz and 0.6 GHz. The analysis were performed according to the IEEE/IEC62704-1 standard and include distributions of electric and magnetic fields around the phantom and antenna. Finally, SAR distributions in the phantom and near the antenna.

Study on response of metal wire in thermoacoustic imaging

Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3[Formula: see text]GHz, 3.0[Formula: see text]GHz, and 5.3[Formula: see text]GHz, and the lengths of copper wires are separately set to 11[Formula: see text]cm, 5[Formula: see text]cm, and 2.5[Formula: see text]cm, the maximum SAR distribution and energy coupling efficiency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11[Formula: see text]cm, 4.77[Formula: see text]cm, and 2.7[Formula: see text]cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.

Adapt2Heat: treatment planning-assisted locoregional hyperthermia by on-line visualization, optimization and re-optimization of SAR and temperature distributions

Background Hyperthermia treatment planning is increasingly used in clinical applications and recommended in quality assurance guidelines. Assistance in phase-amplitude steering during treatment requires dedicated software for on-line visualization of SAR/temperature distributions and fast re-optimization in response to hot spots. As such software tools are not yet commercially available, we developed Adapt2Heat for on-line adaptive hyperthermia treatment planning and illustrate possible application by different relevant real patient examples. Methods Adapt2Heat was developed as a separate module of the treatment planning software Plan2Heat. Adapt2Heat runs on a Linux operating system and was developed in C++, using the open source Qt, Qwt and VTK libraries. A graphical user interface allows interactive and flexible on-line use of hyperthermia treatment planning. Predicted SAR/temperature distributions and statistics for selected phase-amplitude settings can be visualized instantly and settings can be re-optimized manually or automatically in response to hot spots. Results Pretreatment planning E-Field, SAR and temperature calculations are performed with Plan2Heat and imported in Adapt2Heat. Examples show that Adapt2Heat can be helpful in assisting with phase-amplitude steering, e.g., by suppressing indicated hot spots. The effects of phase-amplitude adjustments on the tumor and potential hot spot locations are comprehensively visualized, allowing intuitive and flexible assistance by treatment planning during locoregional hyperthermia treatments. Conclusion Adapt2Heat provides an intuitive and flexible treatment planning tool for on-line treatment planning-assisted hyperthermia. Extensive features for visualization and (re-)optimization during treatment allow practical use in many locoregional hyperthermia applications. This type of tools are indispensable for enhancing the quality of hyperthermia treatment delivery.

Numerical Analysis of SAR and Temperature Distribution in Human Eye Due to Moving Electromagnetic Source

Numerical Analysis of SAR and Temperature Distribution in Human Eye Due to Moving Electromagnetic Source

Feasibility, SAR Distribution, and Clinical Outcome upon Reirradiation and Deep Hyperthermia Using the Hypercollar3D in Head and Neck Cancer Patients.

Simple SummaryFollowing radiotherapy for head and neck cancer, patients are at risk for developing a recurrent or second tumor. Often reirradiation is required in these patients, which is hampered in dose by the previous irradiation. Besides chemotherapy, hyperthermia can potentially increase the effectivity of the radiotherapy. In this study we have used a new hyperthermia applicator in order to increase the effectivity of the radiotherapy in patients requiring reirradiation. We show that the added hyperthermia treatment is tolerated by patients and that we reach a higher hyperthermia dose to the tumor compared to the previous applicator. In addition, we show that the tumor control and survival as well as toxicity are similar compared to what has been reported in literature using chemotherapy as an additive to reirradiation in head and neck cancer patients.(1) Background: Head and neck cancer (HNC) patients with recurrent or second primary (SP) tumors in previously irradiated areas represent a clinical challenge. Definitive or postoperative reirradiation with or without sensitizing therapy, like chemotherapy, should be considered. As an alternative to chemotherapy, hyperthermia has shown to be a potent sensitizer of radiotherapy in clinical studies in the primary treatment of HNC. At our institution, we developed the Hypercollar3D, as the successor to the Hypercollar, to enable improved application of hyperthermia for deeply located HNC. In this study, we report on the feasibility and clinical outcome of patients treated with the Hypercollar3D as an adjuvant to reirradiation in recurrent or SP HNC patients; (2) Methods: We retrospectively analyzed all patients with a recurrent or SP HNC treated with reirradiation combined with hyperthermia using the Hypercollar3D between 2014 and 2018. Data on patients, tumors, and treatments were collected. Follow-up data on disease specific outcomes as well as acute and late toxicity were collected. Data were analyzed using Kaplan Meier analyses; (3) Results: Twenty-two patients with recurrent or SP HNC were included. The average mean estimated applied cfSAR to the tumor volume for the last 17 patients was 80.5 W/kg. Therefore, the novel Hypercollar3D deposits 55% more energy at the target than our previous Hypercollar applicator. In patients treated with definitive thermoradiotherapy a complete response rate of 81.8% (9/11) was observed at 12 weeks following radiotherapy. Two-year local control (LC) and overall survival (OS) were 36.4% (95% CI 17.4–55.7%) and 54.6% (95% CI 32.1–72.4%), respectively. Patients with an interval longer than 24 months from their previous radiotherapy course had an LC of 66.7% (95% CI 37.5–84.6%), whereas patients with a time interval shorter than 24 months had an LC of 14.3% (95% CI 0.7–46.5%) at 18 months (p = 0.01). Cumulative grade 3 or higher toxicity was 39.2% (95% CI 16.0–61.9%); (4) Conclusions: Reirradiation combined with deep hyperthermia in HNC patients using the novel Hypercollar3D is feasible and deposits an average cfSAR of 80.5 W/kg in the tumor volume. The treatment results in high complete response rates at 12 weeks post-treatment. Local control and local toxicity rates were comparable to those reported for recurrent or SP HNC. To further optimize the hyperthermia treatment in the future, temperature feedback is warranted to apply heat at the maximum tolerable dose without toxicity. These data support further research in hyperthermia as an adjuvant to radiotherapy, both in the recurrent as well as in the primary treatment of HNC patients.

Simulation of SAR Induced Heating in Infants undergoing 1.5 T Magnetic Resonance Imaging.

RF absorption in patients undergoing MRI procedures poses a major safety risk due to resulting heating in the tissue. In order to stay below permitted temperature limits the SAR has to be quantified and limited. Based on the model of an infant inside a birdcage coil we have investigated the SAR distribution in the body at 1.5T. Thermal simulations could thus be performed to establish a relationship between the limitations of SAR and temperature. Results show a thermal hotspot in the neck region caused by high local absorption. The temperature limits in this local area were exceeded after 7min of excitation within regulatory SAR limits. For a long-term exposure critical organs in the body's core also undergo thermal stress beyond limitations. This indicates the need for constraints in regard to long MR procedures to consider the temporal aspect of heating.Clinical Relevance-This work establishes a relationship between SAR and temperature in infants undergoing MRI and shows potential risks of long-term procedures due to induced thermal stress.

SAR and temperature distributions in a database of realistic human models for 7 T cardiac imaging.

PurposeTo investigate inter‐subject variability of B 1 +, SAR and temperature rise in a database of human models using a local transmit array for 7 T cardiac imaging.MethodsDixon images were acquired of 14 subjects and segmented in dielectric models with an eight‐channel local transmit array positioned around the torso for cardiac imaging. EM simulations were done to calculate SAR distributions. Based on the SAR distributions, temperature simulations were performed for exposure times of 6 min and 30 min. Peak local SAR and temperature rise levels were calculated for different RF shim settings. A statistical analysis of the resulting peak local SAR and temperature rise levels was performed to arrive at safe power limits.ResultsFor RF shim vectors with random phase and uniformly distributed power, a safe average power limit of 35.7 W was determined (first level controlled mode). When RF amplitude and phase shimming was performed on the heart, a safe average power limit of 35.0 W was found. According to Pennes' model, our numerical study suggests a very low probability of exceeding the absolute local temperature limit of 40 °C for a total exposure time of 6 min and a peak local SAR of 20 W/kg. For a 30 min exposure time at 20 W/kg, it was shown that the absolute temperature limit can be exceeded in the case where perfusion does not change with temperature.ConclusionSafe power constraints were found for 7 T cardiac imaging with an eight‐channel local transmit array, while considering the inter‐subject variability of B 1 +, SAR and temperature rise.

SAR distribution of non-invasive hyperthermia with microstrip applicators on different breast cancer stages

&lt;span&gt;This paper presents the microstrip antenna with different applied frequencies used as a non-invasive hyperthermia applicator. This non-invasive hyperthermia applicator is introduced to clarify the sufficient heat distribution on the treated tissue for different breast cancer stages. 57 mammogram breast cancer images from early-stage to stage-3 are analyzed to obtain the required penetration depth and focus position distance. Then, the simulation-based experiment is carried out to observe the heating distribution on different stages of cancer with two different operating frequencies; 915MHz and 2450MHz. Also included in this paper is the prediction on the period for hyperthermia treatment planning execution. Based on the results, various penetration depths are obtained when different operating frequencies are applied. 915MHz antenna showed better results when compared to 2450MHz, where microstrip applicator with 915MHz is able to heat cancer at stage-1, stage-2, and stage-3 with good penetration depth and focus position distance, while 2450MHz only performed well in early-stage cancer. Meanwhile, different stages require various periods of time. From the results, the shortest period for hyperthermia execution simulated in the early-stage and then followed by stage-3, stage-2, and the longest period is in stage-1.&lt;/span&gt;

Проблематика увеличения пропускной способности каналов мобильной связи и возможные пути решения

In this paper the problem of the growing demand for increasing the capacity of communication channels is considered, using the example of real statistical data of the current mobile operator, and the search for possible ways to solve this issue. The analysis of the distribution of electromagnetic fields and SAR for a three-layer model of the human head when interacting with a cell phone is carried out. The results obtained allow us to conclude that it is impossible to significantly increase the capacity of mobile terminals. The increase in power is accompanied by a significant increase in the spatial peak SAR, which exceeds the value recommended by international standards. As an alternative, the main directions and developments for raising the energy potential in the fifth generation 5G cellular radio channels in the millimeter wavelength range have been identified.

Safety Study of Implant Wearers in MRI RF Field Environment

The complex electromagnetic field environments in magnetic resonance imaging system(MRI) can have a significant impact on patients carrying implants, the RF heating problems being particularly important. To ensure the safety of the patients, it is necessary to understand the distribution of tissue temperature in the MRI environment and its changes over time. Based on the analysis of tissue temperature rise in MRI, this paper constructs a bird cage coil for generating RF field in MRI system, and constructs ASTM standard/improved phantom and single-cavity pacemaker finite element models, use time-domain finite difference (FDTD) to simulate. Firstly, the correctness of the simulation software and simulation method was validated according to the method of ISO. Then the distribution of the electric field, SAR and temperature field and the temperature change with time were calculated in the environment of 64 MHz, 2 W/kg. The difference in temperature rise with blood heat exchange and no blood heat exchange (standard/improved phantom) was specifically compared. The simulation results show that there are electric field and SAR hotspots near the electrode tip, the wire tail and the case of pacemaker. There are high SAR values on both sides of the phantom, and the shorter the distance from the coil, the higher the SAR. The temperature field distribution is similar to the SAR distribution; the temperature is higher in the area around the end of the wire and the case of pacemaker because the heat accumulation is higher around this area. At the same time, blood heat exchange can reduce the temperature rise to a certain extent.

Experimental assessment of clinical MRI-induced global SAR distributions in head phantoms

ObjectiveAccurate estimation of SAR is critical to safeguarding vulnerable patients who require an MRI procedure. The increased static field strength and RF duty cycle capabilities in modern MRI scanners mean that systems can easily exceed safe SAR levels for patients. Advisory protocols routinely used to establish quality assurance protocols are not required to advise on the testing of MRI SAR levels and is not routinely measured in annual medical physics quality assurance checks. This study aims to develop a head phantom and protocol that can independently verify global SAR for MRI clinical scanners. MethodsA four-channel birdcage head coil was used for RF transmission and signal reception. Proton resonance shift thermometry was used to estimate SAR. The SAR estimates were verified by comparing results against two other independent measures, then applied to a further four scanners at field strengths of 1.5 T and 3 T. ResultsScanner output SAR values ranged from 0.42 to 1.52 W/kg. Percentage SAR differences between independently estimated values and those calculated by the scanners differed by 0–2.3%. ConclusionWe have developed a quality assurance protocol to independently verify the SAR output of MRI scanners.

An Extremely Safe Low-SAR Antenna with Study of Its Electromagnetic Biological Effects on Human Head

In this paper, a new low-Specific Absorption Rate (SAR) antenna is proposed for the sake of safe communication in all situations. The proposed antenna involves a Microstrip patch antenna and a metallic casing loop which leads to SAR reduction. The structure operates at 0.9 GHz and 2.4 GHz which produces 0.52 W/kg and 0.25 W/kg SAR value on the human head, respectively. Then, in order to guarantee the antenna safety feature, the experiments are carried out when the human wear an earring. The impact of metallic earrings in different sizes on SAR distribution is investigated. Also, the antenna orientation and rotation effect is considered in detail. It is concluded that the change of Antenna position or use of metallic earrings makes an extremely significant impact on SAR value. But, the results of the presented antenna demonstrate that the produced SAR value in all positions, do not exceed the safe rate. It makes the antenna a suitable candidate for employing in most telecommunication applications.

252. Prediction of subject-specific SAR distribution in MSK MR exam at 7 T

Purpose we predict SAR during MRI exam using a 7 T 1H 298 MHz eight-channel degenerate birdcage coil1 combining SAR simulations with subject-specific measured (RF) B 1 + maps. Materials and Methods We simulated the coil1 in CST MW Suite, loaded by a model of human knee (Fig. 1, top). B 1 + was calculated in an axial slice crossing the patella. The maximum local SAR for an Axial “Zero” Time-of-Echo (ZTE) sequence “SILENT”2 was calculated. We acquired ∣ B 1 , map + ∣ maps of an adult (female) knee with a Bloch-Siegert sequence on 7 axial slices, centered on the same slice of the simulation, on a GE MR950 7T human system. For each slice a coefficient C, proportional to avg ( ∣ B 1 , map + ∣ ) / B 1 , nominal + , was used to scale the SAR simulated3. Results Fig. 1 shows: bottom left, simulated B 1 + magnitude; bottom center, local SAR for an input of 1 W per channel; bottom right, simulated B 1 , nominal + magnitude for a FA = 90° (length = 3.2 ms) sinc-pulse in the slice previously chosen. Fig. 2 shows the subject-specific measured ∣ B 1 , map + ∣ for a FA = 90° sinc-pulse. The predicted SAR obtained with scaled B 1 + maps are 0.50 W/kg (global) and 3.68 W/kg (maximum). Conclusions we obtained a good agreement between simulated and measured in vivo B 1 + maps, and we were able to calculate the distribution of SAR exposure, a safety MRI parameter not available in current exams, where only global SAR is provided, combining simulations and subject-specific measurements. Limits on global and local SAR (20 W/kg) were met for this sequence [1] , [2] , [3] .