Rigorous evaluation of specific absorption rate (SAR) induced in a multilayer biological structure
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This paper compares the specific absorption rate (SAR) values induced in human tissues once obtained when using the equivalent liquid dielectric properties of the equivalent liquid filling the phantom used in SAR measurements and from a model that proposes realistic continuation of tissues in the human body. The calculations are performed for the case of a dipole close to a multilayer structure representing the different body tissues using integral equations techniques solved by the method of moments.Keywords:
Specific absorption rate
Absorption rate
This paper compares the specific absorption rate (SAR) values induced in human tissues once obtained when using the equivalent liquid dielectric properties of the equivalent liquid filling the phantom used in SAR measurements and from a model that proposes realistic continuation of tissues in the human body. The calculations are performed for the case of a dipole close to a multilayer structure representing the different body tissues using integral equations techniques solved by the method of moments.
Specific absorption rate
Absorption rate
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The evaluation of the local Specific Absorption Rate (local SAR) is a major concern in high field Magnetic Resonance (MR) systems. The investigation here presented is focused on the estimation of the Specific Absorption Rate in human head excited by a 7T surface coil. The aim of our work is to evaluate the maximum local SAR of the sample inside the scanner under realistic condition of use. The proposed methodology can be adopted to avoid the over-exposure of the body during the MR exam.
Specific absorption rate
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Specific absorption rate
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This paper compares the specific absorption rate (SAR) values induced in human tissues once obtained when using the equivalent liquid dielectric properties of the equivalent liquid filling the phantom used in SAR measurements and from a model that proposes realistic continuation of tissues in the human body. The calculations are performed for the case of a dipole close to a multilayer structure representing the different body tissues using integral equations techniques solved by the method of moments.
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A specific absorption rate (SAR) estimation system, using a flat-plane solid phantom that provides stable dielectric properties and easy handling of the phantom, is presented. The SAR distribution measured using the solid phantom agrees well with that measured using a liquid phantom, Which is recommended by the International Electrotechnical Commission (IEC), for a standard dipole antenna at 1950 MHz. Calculated mass-averaged SARs, based on the distribution using the solid phantom, have a difference of +2.1% for 10 g and -6.8% for 1 g, respectively, compared to the reference values by IEC. Those results can be improved with a smaller step size of scanning. In addition, in order to decrease the measuring time, the use of two probes is investigated, As a result, the averaged SAR can be obtained with a difference of within 10% with the distance between the two probes of 20 mm.
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This paper evaluates the whole body averaged specific absorption rate (WB-SAR) for a saline-filled standardized phantom in seven different commercial 1.5 T MR systems. Using calorimetry we measured the actual delivered WB-SAR to the phantom. The variability between different MR systems of the actual WB-SAR delivered to the phantom strongly depends on the landmark positions; it ranges for a system estimated WB-SAR of 2 W/kg from 0.6 W/kg at landmark L1 and L2 to 1.2 W/kg for landmark L3. The WB-SAR overestimation ranges from 1.7 to 8.0 depending on the landmark, MR system, and temperature sensor used. The system estimated WB-SAR overestimates the phantom WB-SAR for most cases which can lead to a proportional underestimation of the reported implant heating. Testing in various MR systems using calorimetry to assess the WB-SAR is necessary because of large implant and gel heating variations in different MR systems.
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Comparison the specific absorption rate of the human head model between the second generation (2G)and the fourth generation (4G) of mobile phone communication. rectangular micro strip patch antenna was designed and operated at (1.8 & 2.3) GHz for Global system of mobile communication (GSM)and long term evolution (LTE) applications respectively. Placing the antenna close to the human head model and all the simulation executed using the CST program. The obtained results for the comparison in the second generation is smallest from the specific absorption rate level in the fourth generation, and the specific absorption rate level in (2G and 4G) well below the limitation value recommended by FCC and IEEE.
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The specific absorption rate is used as one of the main safety parameters in magnetic resonance imaging. The performance of imaging sequences is frequently hampered by the limitations imposed on the specific absorption rate that increase in severity at higher field strengths. The most well‐known approach to reducing the specific absorption rate is presumably the variable rate selective excitation technique, which modifies the gradient waveforms in time. In this article, an alternative approach is introduced that uses gradient fields with nonlinear variations in space to reduce the specific absorption rate. The effect of such gradient fields on the relationship between the desired excitation profile and the corresponding radiofrequency pulse is shown. The feasibility of the method is demonstrated using three examples of radiofrequency pulse design. Finally, the proposed method is compared with and combined with the variable rate selective excitation technique. Magn Reson Med 70:537–546, 2013. © 2012 Wiley Periodicals, Inc.
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In order to develop an applicator for microwave hyperthermia, it is necessary to use phantom models to simulate human tissues. In this paper, dry state phantom models which are very stable and easy to handle are studied. The phantom models are made of solid materials and soft materials, which are electrically simulated human muscle and fat. The models are very useful to simulate distribution of specific absorption rate (SAR) inside human tissue model.
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A simplified method for measuring the specific absorption rate (SAR) is required in order to limit the spatial-average SAR for mobile devices in Japan. In this paper, a simplified SAR measurement method involving the use of a flat-plane lightweight phantom composed of a radio wave absorber is proposed. The utility of the lightweight phantom and the feasibility of using the proposed measurement method along with the lightweight phantom are verified. Finally, the peak spatial-average SAR is estimated by using the proposed measurement method.
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