Assessment of the potential threats to brain health posed by the radiation from 5G sub-6 GHz base stations in China using dosimetric methods

The 5G sub-6 GHz radio frequency (RF) electromagnetic fields (EMF) are the most widely used in China's communications. The public has expressed concerns about possible brain health effects of the higher frequency bands in 5G compared to 2G, 3G, and 4G bands. It is imperative to empirically investigate the potential health hazards of these novel frequency bands in 5G communication technology. This study evaluates the assessment of brain tissue dose coupling from sub-6 GHz band EMF emitted by base stations in China. Based on the 3D virtual human body model, the simulation environment was established. Dose including specific absorption rate (SAR) and internal electric field (IEF) between 2G, 3G, and 4G bands and 5G sub-6 GHz was investigated using normalized exposure values and exposure limits. The results indicate that the sub-6 GHz high-frequency band of 5G has the lowest dose value. It can be concluded that high-frequency electromagnetic radiation in 5G sub-6 GHz reduces the dose and health threats to the brain. This provides strong support for the promotion of 5G commutation in China and other regions.

A metamaterial unit-cell based patch radiator for brain-machine interface technology

This paper presents a novel approach to the design of a brain implantable antenna tailored for brain-machine interface (BMI) technology. The design is based on a U-shaped unit-cell metamaterial (MTM), introducing innovative features to enhance performance and address specific challenges associated with BMI applications. The motivation behind the use of the unit-cell structure is to elongate the electric path within the antenna patch, diverging from a reliance on the electrical properties of the MTM. Consequently, the unit cell is connected to an inset-fed transmission line and shorted to the ground. This configuration serves the dual purpose of reducing the size of the antenna and enabling resonance at the 2.442 GHz band within a seven-layer brain phantom. The antenna is designed using a FR-4 substrate (ε r  = 4.3 and tan δ = 0.025) of 1.5 mm thickness, and it is coated with a biocompatible polyamide material (ε r  = 4.3 and tan δ = 0.004) of 0.05 mm thickness. The proposed antenna achieves a compact dimension of 20 × 20 × 1.6 m m 3 (0.338 × 0.338 × 0.027 λ g 3 ) and demonstrates a high bandwidth of 974 MHz with its gain of -14.6 dBi in the 2.442 GHz band. It also exhibits a matched impedance of 49.41-j1.32 Ω in the implantable condition, corresponding to a 50 Ω source impedance. In comparison to a selection of relevant research works, the proposed antenna has a low specific absorption rate (SAR) of 218 W/kg and 68 W/kg at 1g and 10g brain tissue standards, respectively. An antenna prototype has been fabricated and measured for return loss in both free space and in-vivo conditions using sheep's brain. The measurement results are found to be in close agreement with the simulation results for both conditions, showing the practical applicability of the proposed antenna for BMI applications.

Design and performance analysis of an L-shaped radiator and defected ground antenna for enhancing wireless connectivity in brain implants

Brain implantable wireless microsystems has potential to treat neurological diseases and maintain the quality of life. Highly efficient miniaturized antenna is the fundamental part of BID (brain implantable device) for reliable signaling of data through dissipative intracranial material. In this paper, a patch antenna with L-shaped defected ground is demonstrated. L-shaped radiator contributed to achieve the resonance at 2.45 GHz industrial scientific and medical (ISM) band. Antenna size is reduced to 10 × 10 × 0.25 mm3. The proposed L-shaped ground plane geometry is contributing in improving the radiation performance. |S11| value shifts from 15 dB to 30 dB after modifying the ground plane. Proposed structure attained the gain of -14 dBi when located between the Dura and CSF layers at the depth of 12 mm in human brain model. Full wave simulated antenna prototype is fabricated and measured for performance verification. Impedance bandwidth of 270 MHz and broadside radiation pattern (for transferring maximum electromagnetic energy away from tissue) are maintained by the proposed antenna. Brain tissue safety is ensured by specific absorption rate which is 0.709 W/kg and in compliance with the safety limits of 1.6 W/kg for 1-g averaged tissue. Proposed antenna structure is the promising candidate for medical implant technology.

The HL-60 human promyelocytic cell line constitutes an effective in vitro model for evaluating toxicity, oxidative stress and necrosis/apoptosis after exposure to black carbon particles and 2.45 GHz radio frequency

The cellular and molecular mechanisms by which atmospheric pollution from particulate matter and/or electromagnetic fields (EMFs) may prove harmful to human health have not been extensively researched. We analyzed whether the combined action of EMFs and black carbon (BC) particles induced cell damage and a pro-apoptotic response in the HL-60 promyelocytic cell line when exposed to 2.45 GHz radio frequency (RF) radiation in a gigahertz transverse electromagnetic (GTEM) chamber at sub-thermal specific absorption rate (SAR) levels. RF and BC induced moderately significant levels of cell damage in the first 8 or 24 h for all exposure times/doses and much greater damage after 48 h irradiation and the higher dose of BC. We observed a clear antiproliferative effect that increased with RF exposure time and BC dose. Oxidative stress or ROS production increased with time (24 or 48 h of radiation), BC dose and the combination of both. Significant differences between the proportion of damaged and healthy cells were observed in all groups. Both radiation and BC participated separately and jointly in triggering necrosis and apoptosis in a programmed way. Oxidative-antioxidant action activated mitochondrial anti-apoptotic BCL2a gene expression after 24 h irradiation and exposure to BC. After irradiation of the cells for 48 h, expression of FASR cell death receptors was activated, precipitating the onset of pro-apoptotic phenomena and expression and intracellular activity of caspase-3 in the mitochondrial pathways, all of which can lead to cell death. Our results indicate that the interaction between BC and RF modifies the immune response in the human promyelocytic cell line and that these cells had two fates mediated by different pathways: necrosis and mitochondria-caspase dependent apoptosis. The findings may be important in regard to antimicrobial, inflammatory and autoimmune responses in humans.

Specific absorption rate (SAR) simulations for low-field (< 0.1 T) MRI systems

OBJECTIVE

To simulate the magnetic and electric fields produced by RF coil geometries commonly used at low field. Based on these simulations, the specific absorption rate (SAR) efficiency can be derived to ensure safe operation even when using short RF pulses and high duty cycles.

METHODS

Electromagnetic simulations were performed at four different field strengths between 0.05 and 0.1 T, corresponding to the lower and upper limits of current point-of-care (POC) neuroimaging systems. Transmit magnetic and electric fields, as well as transmit efficiency and SAR efficiency were simulated. The effects of a close-fitting shield on the EM fields were also assessed. SAR calculations were performed as a function of RF pulse length in turbo-spin echo (TSE) sequences.

RESULTS

Simulations of RF coil characteristics and B₁⁺ transmit efficiencies agreed well with corresponding experimentally determined parameters. Overall, the SAR efficiency was, as expected, higher at the lower frequencies studied, and many orders of magnitude greater than at conventional clinical field strengths. The tight-fitting transmit coil results in the highest SAR in the nose and skull, which are not thermally sensitive tissues. The calculated SAR efficiencies showed that only when 180° refocusing pulses of duration ~ 10 ms are used for TSE sequences does SAR need to be carefully considered.

CONCLUSION

This work presents a comprehensive overview of the transmit and SAR efficiencies for RF coils used for POC MRI neuroimaging. While SAR is not a problem for conventional sequences, the values derived here should be useful for RF intensive sequences such as T_1ρ, and also demonstrate that if very short RF pulses are required then SAR calculations should be performed.

Evaluation of Chinese populational exposure to environmental electromagnetic field based on stochastic dosimetry and parametric human modelling

This study aimed to estimate the distribution of the whole-body averaged specific absorption rate (WBSAR) using several measurable physique parameters for Chinese adult population exposed to environmental electromagnetic fields (EMFs) of current wireless communication frequencies, and to discuss the effects of these physique parameters in the frequency-dependent dosimetric results. The physique distribution of Chinese adults was obtained from the National Physical Fitness and Health Database comprising 81,490 adult samples. The number of physique parameters used to construct the surrogate model was reduced to three via mutual information analysis. A stochastic method with 40 deterministic simulations was used to generate frequency-dependent and gender-specific surrogate models for WBSAR via polynomial chaos expansion. In the simulations, we constructed anatomically correct models conforming to the targeted physique parameters via deformable human modelling technique, which was based on deep learning from the image database including 767 Chinese adults. Thereafter, we analysed the sensitivity of the physique parameters to WBSAR by covariance-based Sobol decomposition. The results indicated that the generated models were consistent with the targeted physique parameters. The estimated dosimetric results were validated using finite-difference time-domain simulations (the error was < 6% across all the investigated frequencies for WBSAR). The novelty of the study included that it demonstrated the feasibility of estimating the individual WBSAR using a limited number of physique parameters with the aid of surrogate modelling. In addition, the population-based distribution of the WBSAR in Chinese adults was firstly presented in the manuscript. The results also indicated that the different combinations of physique parameter, dependent on genders and frequencies, significantly influenced the WBSAR, although the general conservativeness of the guidelines of the International Commission on Non-Ionizing Radiation and Protection can be confirmed in the surveyed population.

Investigation of extremely low-frequency (1 Hz-400 kHz) pollution frequently encountered in social life: a case study of a shopping mall

It is important to periodically measure, analyze, and map electromagnetic radiation levels due to potential risks. This study aims to draw attention to new electromagnetic pollution caused by radio frequencies and extremely low frequencies. For this reason, electric field and magnetic field measurements were carried out in the 1-Hz-400-kHz frequency band in a shopping mall, where electronic devices cause low-frequency electromagnetic radiation intensively. The measurements were performed with the EHP-50F device for 24 h a day for a week. The measurements were made at 10 points in the shopping mall, and the measurement results were evaluated over five different sectors: electronics, clothing and accessories (male-female), personal care and cosmetics, supermarket, and the playland for children. Magnetic maps of each sector were produced. In addition, the specific absorption rates (SAR) of male and female customers in these workplaces were determined. This is the first study carried out to find SAR caused by low-frequency radiation. Although the safe limit value of SAR for the whole body is 0.08 W/kg, the SAR values calculated in the playland and electronics sectors were obtained to be 0.763 and 0.39 W/kg, respectively. Results clearly demonstrate how especially small children are exposed to danger in the long term.

In silico evaluation of adverse eddy current effects in preclinical tests of magnetic hyperthermia

BACKGROUND AND OBJECTIVE

Magnetic hyperthermia is an oncological therapy that employs magnetic nanoparticles activated by alternating current (AC) magnetic fields with frequencies between 50 kHz and 1 MHz, to release heat in a diseased tissue and produce a local temperature increase of about 5 °C. To assess the treatment efficacy, in vivo tests on murine models (mice and rats) are typically performed. However, these are often carried out without satisfying the biophysical constraints on the electromagnetic (EM) field exposure, with consequent generation of hot spots and undesirable heating of healthy tissues. Here, we investigate possible adverse eddy current effects, to estimate AC magnetic field parameters (frequency and amplitude) that can potentially guarantee safe animal tests of magnetic hyperthermia.

METHODS

The analysis is performed through in silico modelling by means of finite element simulation tools, specifically developed to study eddy current effects in computational animal models, during magnetic hyperthermia treatments. The numerical tools enable us to locally evaluate the specific absorption rate (SAR) and the produced temperature increase, under different field exposure conditions.

RESULTS

The simulation outcomes demonstrate that in mice with weight lower than 30 g the thermal effects induced by AC magnetic fields are very weak, also when slightly overcoming the Hergt-Dutz limit, that is the product of the magnetic field amplitude and frequency should be lower than 5·10⁹ A/(m·s). Conversely, we observe significant temperature increases in 500 g rats, amplified when the field is applied transversally to the body longitudinal axis. A strong mitigation of side-effects can be achieved by introducing water boluses or by applying focused fields.

CONCLUSIONS

The developed physics-based modelling approach has proved to be a useful predictive tool for the optimization of preclinical tests of magnetic hyperthermia, allowing the identification of proper EM field conditions and the design of setups that guarantee safe levels of field exposure during animal treatments. In such contest, the obtained results can be considered as valid indicators to assess reference levels for animal testing of biomedical techniques that involve EM fields, like magnetic hyperthermia, thus complying with the Directive 2010/63/EU on the protection of animals used for scientific purposes.

Volumetric wireless coil for wrist MRI at 1.5 T as a practical alternative to Tx/Rx extremity coil: a comparative study

This work performs a detailed assessment of radiofrequency (RF) safety and imaging performance of a volumetric wireless coil based on periodically coupled split-loop resonators (SLRs) for 1.5 T wrist MRI versus a commercially available transceive extremity coil. In particular, we evaluated the transmit efficiency and RF safety for three setups: a whole-body birdcage coil, a transceive extremity birdcage coil, and a volumetric wireless coil inductively coupled to the whole-body birdcage coil. The imaging performance of the two latter setups was studied experimentally for nine subjects. The signal-to-noise ratio (SNR) of the images acquired with several standard pulse sequences for osteoarthritis wrist imaging was assessed. Application of the wireless coil significantly improved the specific absorption rate (SAR) efficiency of the whole-body birdcage coil, with at least 4.3-fold and 7.6-fold improvement of local and global SAR efficiencies, respectively. This setup also outperformed the transceive extremity coil in terms of SNR (up to 1.40-fold gain) with a moderate (11%) reduction of the local SAR efficiency.

Compressed SENSE in Pediatric Brain Tumor MR Imaging : Assessment of Image Quality, Examination Time and Energy Release

Purpose

To compare the image quality, examination time, and total energy release of a standardized pediatric brain tumor magnetic resonance imaging (MRI) protocol performed with and without compressed sensitivity encoding (C-SENSE). Recently introduced as an acceleration technique in MRI, we hypothesized that C‑SENSE would improve image quality, reduce the examination time and radiofrequency-induced energy release compared with conventional examination in a pediatric brain tumor protocol.

Methods

This retrospective study included 22 patients aged 2.33–18.83 years with different brain tumor types who had previously undergone conventional MRI examination and underwent follow-up C‑SENSE examination. Both examinations were conducted with a 3.0-Tesla device and included pre-contrast and post-contrast T1-weighted turbo-field-echo, T2-weighted turbo-spin-echo, and fluid-attenuated inversion recovery sequences. Image quality was assessed in four anatomical regions of interest (tumor area, cerebral cortex, basal ganglia, and posterior fossa) using a 5-point scale. Reader preference between the standard and C‑SENSE images was evaluated. The total examination duration and energy deposit were compared based on scanner log file analysis.

Results

Relative to standard examinations, C‑SENSE examinations were characterized by shorter total examination times (26.1 ± 3.93 vs. 22.18 ± 2.31 min; P = 0.001), reduced total energy deposit (206.0 ± 19.7 vs. 92.3 ± 18.2 J/kg; P < 0.001), and higher image quality (overall P < 0.001).

Conclusion

C‑SENSE contributes to the improvement of image quality, reduction of scan times and radiofrequency-induced energy release relative to the standard protocol in pediatric brain tumor MRI.

Supplementary Information

The online version of this article (10.1007/s00062-021-01112-3) contains supplementary material, which is available to authorized users.

Average SAR prediction, validation, and evaluation for a compact MR scanner head-sized RF coil

A recently developed compact 3 T (C3T) MRI scanner with high performance gradients [1, 2] has a dedicated radiofrequency (RF) transmit coil that exposes only the head, neck and a small portion of the upper body region during head-first scanning. Due to the unique coil geometry and patient positioning, the established SAR model used for a conventional whole-body scanner cannot be directly translated to the C3T. Here a specific absorption rate (SAR) estimation and validation framework was developed and used to implement a dedicated and accurate SAR prediction model for the C3T. Two different SAR prediction models for the C3T were defined and evaluated: one based on an anatomically derived exposed mass, and one using a fixed anatomical position located caudally to the RF coil to determine the exposed mass. After coil modeling and virtual human body simulation, the designed SAR prediction model was implemented on the C3T and verified with calorimetry and in vivo scan power monitoring. The fixed-demarcation exposed mass model was selected as appropriate exposed mass region to accurately estimate the SAR deposition in the patient on the C3T.

The effect of exposure to radiofrequency electromagnetic fields on cognitive performance in human experimental studies: A protocol for a systematic review

BACKGROUND

The World Health Organization (WHO) is currently assessing the potential health effects of exposure to radiofrequency electromagnetic fields (RF-EMFs) in the general and working population. Related to one such health effect, there is a concern that RF-EMFs may affect cognitive performance in humans. The systematic review (SR) aims to identify, summarize and synthesize the evidence base related to this question. Here, we present the protocol for the planned SR.

OBJECTIVES

The main objective is to present a protocol for a SR which will evaluate the associations between short-term exposure to RF-EMFs and cognitive performance in human experimental studies.

DATA SOURCES

We will search the following databases: PubMed, Embase, Web of Science, Scopus, and the EMF-Portal. The reference lists of included studies and retrieved review articles will be manually searched.

STUDY ELIGIBILITY AND CRITERIA

We will include randomized human experimental studies that assess the effects of RF-EMFs on cognitive performance compared to no exposure or lower exposure. We will include peer-reviewed articles of any publication date in any language that report primary data.

DATA EXTRACTION AND ANALYSIS

Data will be extracted according to a pre-defined set of forms developed and piloted by the review author team. To assess the risk of bias, we will apply the Rating Tool for Human and Animal Studies developed by NTP/OHAT, supplemented with additional questions relevant for cross-over studies. Where sufficiently similar studies are identified (e.g. the heterogeneity concerning population, exposure and outcome is low and the studies can be combined), we will conduct random-effects meta-analysis; otherwise, we will conduct a narrative synthesis.

ASSESSMENT OF CERTAINTY OF EVIDENCE

The certainty of evidence for each identified outcome will be assessed according to Grading of Recommendations Assessment, Development, and Evaluation (GRADE). Performing the review according to this protocol will allow the identification of possible effects of RF-EMFs on cognitive performance in humans. The protocol has been registered in PROSPERO, an open-source protocol registration system, to foster transparency.

Radiofrequency at 2.45 GHz increases toxicity, pro-inflammatory and pre-apoptotic activity caused by black carbon in the RAW 264.7 macrophage cell line

Environmental factors such as air pollution by particles and/or electromagnetic fields (EMFs) are studied as harmful agents for human health. We analyzed whether the combined action of EMF with fine and coarse black carbon (BC) particles induced cell damage and inflammatory response in RAW 264.7 cell line macrophages exposed to 2.45 GHz in a gigahertz transverse electromagnetic (GTEM) chamber at sub-thermal specific absorption rate (SAR) levels. Radiofrequency (RF) dramatically increased BC-induced toxicity at high doses in the first 24 h and toxicity levels remained high 72 h later for all doses. The increase in macrophage phagocytosis induced after 24 h of RF and the high nitrite levels obtained by stimulation with lipopolysaccharide (LPS) endotoxin 24 and 72 h after radiation exposure suggests a prolongation of the innate and inflammatory immune response. The increase of proinflammatory cytokines tumor necrosis factor-α, after 24 h, and of interleukin-1β and caspase-3, after 72 h, indicated activation of the pro-inflammatory response and the apoptosis pathways through the combined effect of radiation and BC. Our results indicate that the interaction of BC and RF modifies macrophage immune response, activates apoptosis, and accelerates cell toxicity, by which it can activate the induction of hypersensitivity reactions and autoimmune disorders.

Metamaterial inspired wireless coil for clinical breast imaging

In this work, we propose an application of a metamaterial inspired volumetric wireless coil (WLC) based on coupled split-loop resonators for targeted breast MRI at 1.5 T. Due to strong electromagnetic coupling with the body coil, the metamaterial inspired WLC locally focuses radiofrequency (RF) magnetic flux in the target region, thus improving both transmit and receive performance of the external body coil. This leads to substantial enhancement in local transmit efficiency and improvement of RF safety. Phantom images showed a tenfold increase of signal-to-noise ratio (SNR) in the region-of-interest (ROI) and, at the same time, an almost 50-fold reduction in transmit power relative to the same body coil used alone.

MRSaiFE: An AI-based Approach Towards the Real-Time Prediction of Specific Absorption Rate

The purpose of this study is to investigate feasibility of estimating the specific absorption rate (SAR) in MRI in real time. To this goal, SAR maps are predicted from 3T- and 7T-simulated magnetic resonance (MR) images in 10 realistic human body models via a convolutional neural network. Two-dimensional (2-D) U-Net architectures with varying contraction layers and different convolutional filters were designed to estimate the SAR distribution in realistic body models. Sim4Life (ZMT, Switzerland) was used to create simulated anatomical images and SAR maps at 3T and 7T imaging frequencies for Duke, Ella, Charlie, and Pregnant Women (at 3, 7, and 9 month gestational stages) body models. Mean squared error (MSE) was used as the cost function and the structural similarity index (SSIM) was reported. A 2-D U-Net with 4 contracting (and 4 expanding) layers and 64 convolutional filters at the initial stage showed the best compromise to estimate SAR distributions. Adam optimizer outperformed stochastic gradient descent (SGD) for all cases with an average SSIM of 90.5∓3.6 % and an average MSE of 0.7∓0.6% for head images at 7T, and an SSIM of >85.1∓6.2 % and an MSE of 0.4∓0.4% for 3T body imaging. Algorithms estimated the SAR maps for 224×224 slices under 30 ms. The proposed methodology shows promise to predict real-time SAR in clinical imaging settings without using extra mapping techniques or patient-specific calibrations.

The cumulative effects and clinical safety of repeat magnetic resonance imaging on an MRI-conditional pacemaker system at 1.5 tesla

Background

Studies have demonstrated magnetic resonance imaging (MRI) safety in the presence of MRI-conditional permanent pacemakers (PPM). However, since patients' care may require serial MRIs, it is necessary to evaluate device safety and performance after multiple scans.

Objectives

We evaluated safety and performance of MRI-conditional PPMs after serial MRIs over various anatomic regions performed during a multicenter, prospective, single-arm study (ProMRI).

Methods

ProMRI was a multiphase observational study designed to evaluate PPM performance after MRI scans. Our study evaluated PPM function in a cohort of patients who underwent multiple 1.5-T MRI scans. Selected patients underwent separate head, chest, and lumbar spine MRIs. Pacing capture threshold (PCT), lead impedance (LI), sensing amplitude, and battery capacity were collected before and after scanning. Freedom from serious adverse device effects (SADE) through 1 month post MRI served as a primary endpoint. Changes in PPM function parameters, including threshold success rate and sensing attenuation, were analyzed for statistical significance and clinical relevance.

Results

In 81 patients no adverse events or SADE occurred. Statistically significant changes in ventricular PCT (0.034 ± 0.15 V) immediately after, ventricular LI immediately after (-18.7 ± 44.2 Ω) and 1 month post phase B (-19.8 ± 44.9 Ω), and atrial sensing attenuation immediately after (-0.27 ± 0.92 mV) and 1 month post phase B (-0.22 ± 0.92 mV) were noted. However, these changes were not clinically relevant in degree.

Conclusion

These results demonstrate the safety and performance of the ProMRI PPM in patients undergoing 3 serial MRIs over various anatomic regions.

Biological effects of radiofrequency fields: Testing a paradigm shift in dosimetry

Biological effects have been reproducibly reported in rodents exposed to radiofrequency fields (RF) without significant change of the body temperature. These observations relaunch the controversial question of non-thermal effects of RF. If true, such effects would imply to consider RF energy absorption/interaction in tissues, not as volume-averaged, but locally down to the microscale, which is of potential consequence in particular at frequencies beyond 3 GHz. We propose study protocols to explore that question.

The potential of magnetic heating for fabricating Pickering-emulsion-based capsules

Pickering emulsions (particle-stabilized emulsions) have been widely explored due to their potential applications, one of which is using them as precursors for the formation of colloidal capsules that could be utilized in, among others, the pharmacy and food industries. Here, we present a novel approach to fabricating such colloidal capsules by using heating in the alternating magnetic field. When exposed to the alternating magnetic field, magnetic particles, owing to the hysteresis and/or relaxation losses, become sources of nano- and micro-heating that can significantly increase the temperature of the colloidal system. This temperature rise was evaluated in oil-in-oil Pickering emulsions stabilized by both magnetite and polystyrene particles. When a sample reached high enough temperature, particle fusion caused by glass transition of polystyrene was observed on surfaces of colloidal droplets. Oil droplets covered with shells of fused polystyrene particles were proved to be less susceptible to external stress, which can be evidence of the successful formation of capsules from Pickering emulsion droplets as templates.

A stable miniaturised AMC loaded flexible monopole antenna for ingestible applications

This paper proposes an ultra-miniaturised, flexible 5.8 GHz antenna to give better performance for an ingestible wireless capsule endoscopy system. The use of an artificial magnetic conductor (AMC) unit cell in this design helps in enhancing the gain, improving the efficiency and reducing the size at resonance. This novel AMC-based layer is modelled as a radiator, and is excited by a complementary strip feed. The proposed design is printed on a flexible polyimide material of size 4.6 × 7.6 × 0.15 mm, with dielectric constant 3.5 and loss tangent 0.008. The antenna has an omni-directional radiation pattern with gain 1.64 dBi. The size is reduced drastically by bending the structure to fit inside a standard-sized ingestible capsule of 26 × 11 mm. The performance metrics of the antenna after placing inside the wireless ingestible capsule are presented with the help of an analysis of the reflection coefficient curves, radiation pattern, specific absorption rate (SAR) and field distributions. In addition, different positions and orientations of the antenna and different bending conditions are used, and these cases are solved using our AMC-based unit cell radiator. We carry out simulations using High Frequency Structure Simulator (HFSS) and measurements are made by immersing the fabricated antenna in minced meat. The results of this novel structure are compared with those of other ingestible antennas proposed in the literature. The proposed design has a SAR value of 0.82505 W/kg at around 5.8 GHz over 1 g of tissue, thereby redirecting the radiation away from the human body. This conformal AMC structure achieved better miniaturisation while maintaining the antenna resonance and SAR within permissible limits.

Heating Efficiency of Triple Vortex State Cylindrical Magnetic Nanoparticles

A well-established method for treating cancerous tumors is magnetic hyperthermia, which uses localized heat generated by the relaxation mechanism of magnetic nanoparticles (MNPs) in a high-frequency alternating magnetic field. In this work, we investigate the heating efficiency of cylindrical NiFe MNPs, fabricated by template-assisted pulsed electrodeposition combined with differential chemical etching. The cylindrical geometry of the MNP enables the formation of the triple vortex state, which increases the heat generation efficiency by four times. Using time-dependent calorimetric measurements, the specific absorption rate (SAR) of the MNPs was determined and compared with the numerical calculations from micromagnetic simulations and vibrating sample magnetometer measurements. The magnetization reversal of high aspect ratios MNPs showed higher remanent magnetization and low-field susceptibility leading to higher hysteresis losses, which was reflected in higher experimental and theoretical SAR values. The SAR dependence on magnetic field strength exhibited small SAR values at low magnetic fields and saturates at high magnetic fields, which is correlated to the coercive field of the MNPs and a characteristic feature of ferromagnetic MNPs. The optimization of cylindrical NiFe MNPs will play a pivotal role in producing high heating performance and biocompatible magnetic hyperthermia agents.

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

OBJECTIVE

Accurate 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.

METHODS

A 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.

RESULTS

Scanner 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%.

CONCLUSION

We have developed a quality assurance protocol to independently verify the SAR output of MRI scanners.

[Implant clarification : Management in clinical practice]

BACKGROUND

The increasing number of magnetic resonance imaging (MRI) examinations and the increasing number of medical implants lead to an ever-increasing expenditure in implant research, which as a consequence is becoming more time and resource consuming.

MATERIAL AND METHODS

This review article provides guidelines for optimized implant clarification in clinical practice by means of patient interrogation and the incorporation of implant databases. The technical background of implant interactions is discussed and an outlook on new integrated MRI safety systems is given.

CONCLUSION

The optimization of the implant clarification process integrated into the clinical workflow avoids undesired MRI interactions and enables a safe and economic working procedure for patients.

Mobile phones: A trade-off between speech intelligibility and exposure to noise levels and to radio-frequency electromagnetic fields

When making phone calls, cellphone and smartphone users are exposed to radio-frequency (RF) electromagnetic fields (EMFs) and sound pressure simultaneously. Speech intelligibility during mobile phone calls is related to the sound pressure level of speech relative to potential background sounds and also to the RF-EMF exposure, since the signal quality is correlated with the RF-EMF strength. Additionally, speech intelligibility, sound pressure level, and exposure to RF-EMFs are dependent on how the call is made (on speaker, held at the ear, or with headsets). The relationship between speech intelligibility, sound exposure, and exposure to RF-EMFs is determined in this study. To this aim, the transmitted RF-EMF power was recorded during phone calls made by 53 subjects in three different, controlled exposure scenarios: calling with the phone at the ear, calling in speaker-mode, and calling with a headset. This emitted power is directly proportional to the exposure to RF EMFs and is translated into specific absorption rate using numerical simulations. Simultaneously, sound pressure levels have been recorded and speech intelligibility has been assessed during each phone call. The results show that exposure to RF-EMFs, quantified as the specific absorption in the head, will be reduced when speaker-mode or a headset is used, in comparison to calling next to the ear. Additionally, personal exposure to sound pressure is also found to be highest in the condition where the phone is held next to the ear. On the other hand, speech perception is found to be the best when calling with a phone next to the ear in comparison to the other studied conditions, when background noise is present.

Mobile phone antenna-matching study with different finger positions on an inhomogeneous human model

The human head and hand being in the near-field zone of a mobile phone antenna can drastically influence the antenna matching with free space. The goal of the presented research is to study this phenomenon on an inhomogeneous human model for different relative positions and distances of hand and fingers when using a mobile phone. The only safety criteria commonly used to estimate RF exposure impact on humans is the specific absorption rate (SAR). Its limits are determined by the Federal Communication Commission (FCC) in the USA and the International Commission on Non-Ionizing Radiation Protection (ICNIRP) in Europe. The maximal values of SAR for a mobile handset are determined for each model by the manufacturer. In this paper, it is shown that the peak values provided by the manufacturers and their understanding may need refinement. It is almost impossible to consider all parameters, such as the dependence of SAR on antenna communication matching, with a variety of shapes and forms and other details during physical measurements or numerical estimation. The premise for such assumptions is based on the analysis of S11 dependency on the exposure scenario and the fact that the Automatic Gain Control (AGC) increases power when the signal strength at the base station drops.

Effects of a brain tumor in a dispersive human head on SAR and temperature rise distributions due to RF sources at 4G and 5G frequencies

In this paper, effects of a brain tumor located in a dispersive human head model on specific absorption rate (SAR) and temperature rise distributions due to different types of RF sources at 4G and 5G cellular frequencies are investigated with the use of a multiphysics model. This multiphysics model analyzes the dispersive human head with the brain tumor and provides the SAR and temperature rise distributions in the head due to the RF source operated at 4G and 5G cellular frequencies in a single finite-difference time-domain simulation. An adjacent antenna operated at 4G and 5G cellular frequencies to the human head is considered as the RF source for near-field exposure, while a plane wave field radiated by base stations operated at 4G and 5G cellular frequencies is considered as the RF source for far-field exposure. Numerical results show that the brain tumor in the head slightly affects the SAR and temperature rise distributions due to different RF sources at 4G and 5G cellular frequencies.

Absorption of wireless radiation in the child versus adult brain and eye from cell phone conversation or virtual reality

Children's brains are more susceptible to hazardous exposures, and are thought to absorb higher doses of radiation from cell phones in some regions of the brain. Globally the numbers and applications of wireless devices are increasing rapidly, but since 1997 safety testing has relied on a large, homogenous, adult male head phantom to simulate exposures; the "Standard Anthropomorphic Mannequin" (SAM) is used to estimate only whether tissue temperature will be increased by more than 1 Celsius degree in the periphery. The present work employs anatomically based modeling currently used to set standards for surgical and medical devices, that incorporates heterogeneous characteristics of age and anatomy. Modeling of a cell phone held to the ear, or of virtual reality devices in front of the eyes, reveals that young eyes and brains absorb substantially higher local radiation doses than adults'. Age-specific simulations indicate the need to apply refined methods for regulatory compliance testing; and for public education regarding manufacturers' advice to keep phones off the body, and prudent use to limit exposures, particularly to protect the young.

SERIAL transmit - parallel receive (STxPRx) MR imaging produces acceptable proton image uniformity without compromising field of view or SAR guidelines for human neuroimaging at 9.4 Tesla

PURPOSE

Non-uniform B1⁺ excitation and high specific absorption rates (SAR) compromise proton MR imaging of human brain at 9.4 T (400.5 MHz). By combining a transmit/receive surface coil array using serial transmission of individual coils with a total generalized variation reconstruction of images from all coils, acceptable quality human brain imaging is demonstrated.

METHODS

B₀ is shimmed using sodium MR imaging (105.4 MHz) with a birdcage coil. Proton MR imaging is performed with an excitation/receive array of surface coils. The modified FLASH pulse sequence transmits serially across each coil within the array thereby distributing SAR in time and space. All coils operate in receive mode. Although the excitation profile of each transmit coil is non-uniform, the sensitivity profile estimated from the non-transmit receive coils provides an acceptable sensitivity correction. Signals from all coils are combined in a total generalized variation (TGV) reconstruction to provide a full field of view image at maximum signal to noise (SNR) performance.

RESULTS

High-resolution images across the human head are demonstrated with acceptable uniformity and SNR.

CONCLUSION

Proton MR imaging of the human brain is possible with acceptable uniformity at low SAR at 9.4 Tesla using this serial excitation and parallel reception strategy with TGV reconstruction.

Assessment of MRI issues at 1.5 T for the Temperature Logger Implant

PURPOSE

The Temperature Logger Implant is a newly developed device that is capable of providing data for animal studies on thermoregulatory function, hibernation, hypothermia, and general health. During research, it may be necessary to conduct a magnetic resonance imaging (MRI) examination on an animal with this device implanted to assess anatomical changes or other conditions. Notably, this new device was specially designed to be unaffected by the electromagnetic fields used for MRI. Therefore, to verify that there would be no problems related to MRI, the purpose of this investigation was to evaluate MRI-related issues for the Temperature Logger Implant.

METHODS

Tests were performed on the Temperature Logger Implant using well-accepted techniques to evaluate magnetic field interactions (translational attraction and torque, 1.5 T), MRI-related heating (whole body averaged specific absorption rate, 2.9 W/kg), artifacts (T1-weighted, spin echo and gradient echo pulse sequences), and functional changes related to exposure to eight different imaging conditions.

RESULTS

Magnetic field interactions were relatively low (deflection angle 4°, no torque) and heating was minor (highest temperature rise, > 1.1 °C) indicating that these factors will not pose a hazard to an animal. The largest artifact (gradient echo pulse sequence) extended 10 mm from the size and shape of the Temperature Logger Implant. Exposure to the eight different conditions at 1.5 T/ 64 MHz did not alter or damage the operational aspects of the device.

CONCLUSIONS

The findings demonstrated that MRI can be performed safely on an animal with this new Temperature Logger Implant and, thus, this device is deemed "MR Conditional" (i.e., using current labeling terminology), according to the conditions used in this investigation.

Experimental investigation of a metasurface resonator for in vivo imaging at 1.5 T

In this work, we experimentally demonstrate an increase in the local transmit efficiency of a 1.5 T MRI scanner by using a metasurface formed by an array of brass wires embedded in a high permittivity low loss medium. Placement of such a structure inside the scanner results in strong coupling of the radiofrequency field produced by the body coil with the lowest frequency electromagnetic eigenmode of the metasurface. This leads to spatial redistribution of the near fields with enhancement of the local magnetic field and an increase in the transmit efficiency per square root maximum specific absorption rate in the region-of-interest. We have investigated this structure in vivo and achieved a factor of 3.3 enhancement in the local radiofrequency transmit efficiency.

Interaction Effects in Assembly of Magnetic Nanoparticles

A specific absorption rate of a dilute assembly of various random clusters of iron oxide nanoparticles in alternating magnetic field has been calculated using Landau-Lifshitz stochastic equation. This approach simultaneously takes into account both the presence of thermal fluctuations of the nanoparticle magnetic moments and magneto-dipole interaction between the nanoparticles of the clusters. It is shown that for usual 3D clusters, the intensity of the magneto-dipole interaction is determined mainly by the cluster packing density η = N _p V/V _cl , where N _p is the average number of the particles in the cluster, V is the nanoparticle volume, and V _cl is the cluster volume. The area of the low frequency hysteresis loop and the assembly-specific absorption rate have been found to be considerably reduced when the packing density of the clusters increases in the range of 0.005 ≤ η < 0.4. The dependence of the specific absorption rate on the mean nanoparticle diameter is retained with an increase of η, but becomes less pronounced. For fractal clusters of nanoparticles, which arise in biological media, in addition to a considerable reduction of the absorption rate, the absorption maximum is shifted to smaller particle diameters. It is found also that the specific absorption rate of fractal clusters increases appreciably with an increase of the thickness of nonmagnetic shells at the nanoparticle surfaces.

Assessment of MRI issues for a new cerebral spinal fluid shunt, gravitational valve (GV)

PURPOSE

A gravitational valve (GV) may be used to treat hydrocephalus, offering possible advantages that include avoidance of over drainage and long-term complications. Because a GV is made from metal, there are potential safety and other problems related to the use of MRI. The objective of this investigation was to evaluate MRI-related issues (i.e., magnetic field interactions, heating, and artifacts) for a newly developed, metallic GV.

METHODS

Tests were performed on the GV (GAV 2.0) using well-accepted techniques to assess magnetic field interactions (translational attraction and torque, 3-Tesla), MRI-related heating (1.5-T/64-MH and 3-T/128-MHz, whole body averaged SAR, 2.7-W/kg and 2.9-W/kg, respectively), artifacts (3-Tesla; gradient echo and T1-weighted, spin echo sequences), and possible functional changes related to exposures to different MRI conditions (exposing six samples each to eight different pulse sequences at 1.5-T/64-MHz and 3-T/128-MHz).

RESULTS

Magnetic field interactions were not substantial (deflection angle 2°, no torque) and heating was minor (highest temperature rise, ≥1.9°C, highest background temperature rise, ≥1.7°C). Artifacts on the gradient echo pulse sequence extended approximately 10mm from the size and shape of the GV. The different exposures to 1.5-T/64-MHz and 3-T/128-MHz conditions did not alter or damage the operational aspects of the GV samples.

CONCLUSIONS

The findings demonstrated that MRI can be safely used in patients with this GV and, thus, this metallic implant is deemed acceptable or "MR Conditional" (i.e., using current labeling terminology), according to the conditions used in this study.

Hysteresis losses and specific absorption rate measurements in magnetic nanoparticles for hyperthermia applications

BACKGROUND

Magnetic hysteresis loops areas and hyperthermia on magnetic nanoparticles have been studied with the aim of providing reliable and reproducible methods of measuring the specific absorption rate (SAR).

METHODS

The SAR of Fe₃O₄ nanoparticles with two different mean sizes, and Ni_1-xZn_xFe₂O₄ ferrites with 0 ≤ x ≤ 0.8 has been measured with three approaches: static hysteresis loops areas, dynamic hysteresis loops areas and hyperthermia of a water solution. For dynamic loops and thermometric measurements, specific experimental setups have been developed, that operate at comparable frequencies (≈ 69kHz and ≈ 100kHz respectively) and rf magnetic field peak values (up to 100mT). The hyperthermia setup has been fully modelled to provide a direct measurement of the SAR of the magnetic nanoparticles by taking into account the heat exchange with the surrounding environment in non-adiabatic conditions and the parasitic heating of the water due to ionic currents.

RESULTS

Dynamic hysteresis loops are shown to provide an accurate determination of the SAR except for superparamagnetic samples, where the boundary with a blocked regime could be crossed in dynamic conditions. Static hysteresis loops consistently underestimate the specific absorption rate but can be used to select the most promising samples.

CONCLUSIONS

A means of reliably measure SAR of magnetic nanoparticles by different approaches for hyperthermia applications is presented and its validity discussed by comparing different methods.

GENERAL SIGNIFICANCE

This work fits within the general subject of metrological traceability in medicine with a specific focus on magnetic hyperthermia. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Determining iron oxide nanoparticle heating efficiency and elucidating local nanoparticle temperature for application in agarose gel-based tumor model

Magnetic iron oxide nanoparticles (MNPs) have been developed for magnetic fluid hyperthermia (MFH) cancer therapy, where cancer cells are treated through the heat generated by application of a high frequency magnetic field. This heat has also been proposed as a mechanism to trigger release of chemotherapy agents. In each of these cases, MNPs with optimal heating performance can be used to maximize therapeutic effect while minimizing the required dosage of MNPs. In this study, the heating efficiencies (or specific absorption rate, SAR) of two types of MNPs were evaluated experimentally and then predicted from their magnetic properties. MNPs were also incorporated in the core of poly(ethylene glycol-b-caprolactone) micelles, co-localized with rhodamine B fluorescent dye attached to polycaprolactone to monitor local, nanoscale temperatures during magnetic heating. Despite a relatively high SAR produced by these MNPs, no significant temperature rise beyond that observed in the bulk solution was measured by fluorescence in the core of the magnetic micelles. MNPs were also incorporated into a macro-scale agarose gel system that mimicked a tumor targeted by MNPs and surrounded by healthy tissues. The agarose-based tumor models showed that targeted MNPs can reach hyperthermia temperatures inside a tumor with a sufficient MNP concentration, while causing minimal temperature rise in the healthy tissue surrounding the tumor.

Bovine Serum Albumin-Conjugated Ferrimagnetic Iron Oxide Nanoparticles to Enhance the Biocompatibility and Magnetic Hyperthermia Performance

ABSTRACT

Magnetic hyperthermia is a fast emerging, non-invasive cancer treatment method which is used synergistically with the existing cancer therapeutics. We have attempted to address the current challenges in clinical magnetic hyperthermia-improved biocompatibility and enhanced heating characteristics, through a single combinatorial approach. Both superparamagnetic iron oxide nanoparticles (SPIONs) of size 10 nm and ferrimagnetic iron oxide nanoparticles (FIONs) of size 30 nm were synthesized by thermal decomposition method for comparison studies. Two different surface modifying agents, viz, Cetyl Trimethyl Ammonium Bromide and 3-Aminopropyltrimethoxysilane, were used to conjugate Bovine Serum Albumin (BSA) over the iron oxide nanoparticles via two different methods-surface charge adsorption and covalent amide bonding, respectively. The preliminary haemolysis and cell viability experiments show that BSA conjugation mitigates the haemolytic effect of the iron oxide nanoparticles on erythrocytes and is non-cytotoxic to the healthy Baby Hamster Kidney cells. It was observed from the results that due to better colloidal stability, the SAR value of the BSA-iron oxide nanoparticles is higher than the iron oxide nanoparticles without BSA, irrespective of the size of the iron oxide nanoparticles and method of conjugation. The BSA-FIONs seem to show improved biocompatibility, as the haemolytic index is less than 2 % and cell viability is up to 120 %, when normalized with the control. The SAR value of BSA-FIONs is 2300 W g^-1 when compared to 1700 W g^-1 of FIONs without BSA conjugation. Thus, we report here that BSA conjugation over FIONs (with a high saturation magnetization of 87 emu g^-1) provide a single combinatorial approach to improve the biocompatibility and enhance the SAR value for magnetic hyperthermia, thus addressing both the current challenges of the same.

Polyethylene Glycol-Mediated Synthesis of Cubic Iron Oxide Nanoparticles with High Heating Power

Iron oxide magnetic nanoparticles (IOMNPs) have been successfully synthesized by means of solvothermal reduction method employing polyethylene glycol (PEG200) as a solvent. The as-synthesized IOMNPs are poly-dispersed, highly crystalline, and exhibit a cubic shape. The size of IOMNPs is strongly dependent on the reaction time and the ration between the amount of magnetic precursor and PEG200 used in the synthesis method. At low magnetic precursor/PEG200 ratio, the cubic IOMNPs coexist with polyhedral IOMNPs. The structure and morphology of the IOMNPs were thoroughly investigated by using a wide range of techniques: TEM, XRD, XPS, FTIR, and RAMAN. XPS analysis showed that the IOMNPs comprise a crystalline magnetite core bearing on the outer surface functional groups from PEG200 and acetate. The presence of physisorbed PEG200 on the IOMNP surface is faintly detected through FT-IR spectroscopy. The surface of IOMNPs undergoes oxidation into maghemite as proven by RAMAN spectroscopy and the occurrence of satellite peaks in the Fe2p XP spectra. The magnetic studies performed on powder show that the blocking temperature (TB) of IOMNPs is around 300 K displaying a coercive field in between 160 and 170 Oe. Below the TB, the field-cooled (FC) curves turn concave and describe a plateau indicating that strong magnetic dipole-dipole interactions are manifested in between IOMNPs. The specific absorption rate (SAR) values increase with decreasing nanoparticle concentrations for the IOMNPs dispersed in water. The SAR dependence on the applied magnetic field, studied up to magnetic field amplitude of 60 kA/m, presents a sigmoid shape with saturation values up to 1700 W/g. By dispersing the IOMNPs in PEG600 (liquid) and PEG1000 (solid), it was found that the SAR values decrease by 50 or 75 %, indicating that the Brownian friction within the solvent was the main contributor to the heating power of IOMNPs.

Optimization of synthesis and peptization steps to obtain iron oxide nanoparticles with high energy dissipation rates

Magnetic Fluid Hyperthermia (MFH) uses heat generated by magnetic nanoparticles exposed to alternating magnetic fields to cause a temperature increase in tumors to the hyperthermia range (43-47 °C), inducing apoptotic cancer cell death. As with all cancer nanomedicines, one of the most significant challenges with MFH is achieving high nanoparticle accumulation at the tumor site. This motivates development of synthesis strategies that maximize the rate of energy dissipation of iron oxide magnetic nanoparticles, preferable due to their intrinsic biocompatibility. This has led to development of synthesis strategies that, although attractive from the point of view of chemical elegance, may not be suitable for scale-up to quantities necessary for clinical use. On the other hand, to date the aqueous co-precipitation synthesis, which readily yields gram quantities of nanoparticles, has only been reported to yield sufficiently high specific absorption rates after laborious size selective fractionation. This work focuses on improvements to the aqueous co-precipitation of iron oxide nanoparticles to increase the specific absorption rate (SAR), by optimizing synthesis conditions and the subsequent peptization step. Heating efficiencies up to 1,048 W/g_Fe (36.5 kA/m, 341 kHz; ILP = 2.3 nH·m²·kg^-1) were obtained, which represent one of the highest values reported for iron oxide particles synthesized by co-precipitation without size-selective fractionation. Furthermore, particles reached SAR values of up to 719 W/g_Fe (36.5 kA/m, 341 kHz; ILP = 1.6 nH·m²·kg^-1) when in a solid matrix, demonstrating they were capable of significant rates of energy dissipation even when restricted from physical rotation. Reduction in energy dissipation rate due to immobilization has been identified as an obstacle to clinical translation of MFH. Hence, particles obtained with the conditions reported here have great potential for application in nanoscale thermal cancer therapy.

A far-field radio-frequency experimental exposure system with unrestrained mice

Many studies have been performed on exploring the effects of radio-frequency (RF) energy on biological function in vivo. In particular, gene expression results have been inconclusive due, in part, to a lack of a standardized experimental procedure. This research describes a new far field RF exposure system for unrestrained murine models that reduces experimental error. The experimental procedure includes the materials used, the creation of a patch antenna, the uncertainty analysis of the equipment, characterization of the test room, experimental equipment used and setup, power density and specific absorption rate experiment, and discussion. The result of this research is an experimental exposure system to be applied to future biological studies.

Surface coil with reduced specific absorption rate for rat MRI at 7 T

OBJECTIVE

A scaled-down slotted surface radio frequency (RF) coil was built, and the specific absorbance rate (SAR) in 100 mg of tissue (SAR100 mg) produced in a rat brain phantom was computed at 7 T.

MATERIALS AND METHODS

A slotted coil 2-cm in diameter with six circular slots was developed. Its theoretical and experimental performance was computed and compared using the signal-to-noise ratio (SNR) expression and phantom images obtained with a spin echo sequence. Electromagnetic simulations were performed using the finite integral method with saline sphere and rat brain phantoms. SAR100 mg was computed for the circular coil, by varying its radius, and was also computed for the slotted coil.

RESULTS

The slotted coil quality factor gave a twofold increment over the circular coil, and noise was reduced by 17%. The experimental SNR of the slotted coil produced a 30% improvement for points near the coil plane. The theoretical and experimental results showed substantial agreement. Axial map histograms and profiles showed greater SAR100 mg values for the circular coil than for the slotted coil.

CONCLUSIONS

The slotted surface coil offers improved performance and low SAR100 mg for rat brain imaging at 7 T. This approach may be used with new RF coils to investigate SAR in humans.

Bioelectromagnetic effects measurements - SAR and induced current

The paper discusses several theoretical and practical aspects of the application of currents flowing through the body of a radiotelephone operator and Specific Absorption Rate (SAR). SAR is known as the physical quantity which is a perfect solution for biological experiments. Unfortunately, SAR cannot be measured directly. Contrary to SAR, which is limited to the penetration depth, a current induced in a point of a body is measurable in any other point of the body. The main objective of this paper is to show that the current induced in a human body when using a radiotelephone or mobile phone is significant and should be analyzed as widely as SAR is. Computer simulations of a human's hand with a radiotelephone were made. Experiments were also conducted. The results of the experiments show that induced current is also as important as SAR and it cannot be omitted in bioelectromagnetic experiments. In biomedical studies both parameters: induced current and SAR play a major role.

Recent advances in MRI technology: Implications for image quality and patient safety

Recent advances in MRI technology are presented, with emphasis on how this new technology impacts clinical operations (better image quality, faster exam times, and improved throughput). In addition, implications for patient safety are discussed with emphasis on the risk of patient injury due to either high local specific absorption rate (SAR) or large cumulative energy doses delivered during long exam times. Patient comfort issues are examined as well.