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Magnetic Resonance Imaging Physics
Published in Debbie Peet, Emma Chung, Practical Medical Physics, 2021
SAR limits have been set for specific areas of the body (e.g. the head) and must not be exceeded. Scanners include safety features to limit the SAR so that RF deposition is within standard limits set by organisations such as the International Electrotechnical Commission (IEC). For the SAR to be correctly calculated by the scanner software, it is critical to enter the patient’s correct weight and to follow the manufacturer’s safety instructions. Failure to do so may result in incorrect calculation of SAR limits, which may result in patient heating or burns. The SAR applied to the body is also dependent on the temperature and humidity within the bore.
Radiofrequency Fields
Published in Bertil R. R. Persson, Freddy Ståhlberg, Health and Safety of Clinical NMR Examinations, 2019
Bertil R. R. Persson, Freddy Ståhlberg
The specific absorption rate “SAR” corresponds to the rate of specific absorbed electromagnetic power in tissue. The absorbed power in the irradiated body depends on the electric conductivity (σ) and density (ρ) of the medium and the square of the electric fields strength (E). For a sinusoidal wave the effective field strength is where Eo is the peak value. With the above notations, the rate of specific absorbed power is given by:
Evaluation of Hyperthermia Equipment
Published in Leopold J. Anghileri, Jacques Robert, Hyperthermia in Cancer Treatment, 2019
In Figure 1A is shown a typical CT scan and in Figure IB the finite element grid superimposed on the digitized outline of the major tissue regions. In Figure 2 is shown the contours of iso-SAR values for this patient model calculated using the finite element method.11 The term SAR stands for specific absorption rate and is equal to the power absorbed per unit volume of tissue (watt/kg). To generate these iso-SAR curves the magnetic intensity, H(x,y), is calculated using the finite element method, and then the electric field is calculated from where ω = radian frequency, E = electric field, ∈ = dielectric constant, and σ = electrical conductivity. The SAR or absorbed power density is then found from
Multi-criterion optimization of invasive antenna applicators for Au@Fe3O4, Au@-Fe2O3 and Au@-Fe2O3 mediated microwave ablation treatment
Published in Electromagnetic Biology and Medicine, 2023
Alka Singla, Anupma Marwaha, Sanjay Marwaha
Here, Table 1. From Figure 12(d) it can be seen that maximum SAR value is obtained while the healthy tissues remain safe. The MNP characteristics such as its size and composition play an important role in the heating mechanism and liver tissue SAR distribution. It is analyzed that with the increase in radius of MNP, higher SAR values are obtained for all the three composites of MNP. Though the increase in size of 25 nm and 30 nm enhances the value of SAR i.e.10 kW/kg and 11 kW/kg but as discussed in previous section, increase in core radius also increments the temperature, which is not in the permissible limits of ablation treatment for core radius above 20 nm. Further it is noticeable that the magnetite (Fe3O4) of size 20 nm gives much localized SAR with maximum value of 9.5 kW/kg while the other composites such as hematite and maghemite give maximum SAR values of 8.9 kW/kg and 4.4 kW/kg respectively.
Effects of radiofrequency radiation on apoptotic and antiapoptotic factors in colorectal cancer cells
Published in Electromagnetic Biology and Medicine, 2022
Sanem Gökçen, Berrak Kurt, Yusuf Küçükbağrıaçık, Elcin Ozgur-Buyukatalay, Görkem Kismali
The International Commission of Non-Ionizing Radiation Protection Center (ICNIRP) declares that RFR may have thermal and non-thermal effects on bodies. While thermal effects are very much expected, non-thermal effects are called biological effects in which these effects occur without increasing the temperature of the tissue (ICNIRP, 1998). According to the commission’s guidelines, The Specific Absorption Rate (SAR), which is defined as the electromagnetic energy absorbed by the body, is used to evaluate the biological effects of RFR if it is thermal or non-thermal. The amount of electromagnetic energy that increases the temperature of 1 kg of the body by 1°C, which absorbs RF energy, is defined as 4 W. Whole body SAR value as 0.4 W/kg, which is 10 times lower than this value, is accepted as the value at which the limit thermal effects begin (WHO 1998). Although the mechanism of heating effect of RFR is known as rotational motion of the singlet electron of the molecules, researchers try to enlighten the mechanism of non-thermal effects, one of which is apoptotic pathways. Apoptosis is a mechanism that causes programmed cell death leading to cell shrinkage, nuclear fragmentation, and chromatin condensation (Su et al. 2015). The apoptotic pathway, stimulated by extrinsic and intrinsic factors, is regulated by caspase family aspartate-specific proteases (Kischkel et al. 1995).
A novel and effective technique to reduce electromagnetic radiation absorption on biotic components at 2.45 GHz
Published in Electromagnetic Biology and Medicine, 2022
Meenu L, Aiswarya S, Sreedevi K. Menon
This experiment is a direct validation and serves as a proof of concept that the EMR exposure rate, time and intensity has an adverse effect on the plant tissues. The study shows that the variation in secretion of plant hormones like Gibberellins, Cytokinins, Abscisic Acid and Auxins had led to the retardation in the complete growth of the plant (Naqvi 1999) – (Arteca 1996.). The radiation is mainly due to the antenna present in the gadgets and these radiations will be absorbed by the vegetation. This is measured in terms of SAR for a given tissue. SAR depends upon dielectric property, conductivity, mass density, electric field strength of the tissues etc. The absorption of radiation by pea seeds near to the router is more as it receives more power in the vicinity of the router. So the variation in absorption results in growth retardation even from its initial stage of the germination. This effect in the sprouting stage makes changes in the entire life cycle of each plant community. These continuous exposure reduces the nutrient capability of vegetations and it makes them unhealthy to human life.