Comparative study of shortwave heating patterns in phantoms with polyethylene and silk partitions

Specific absorption rate (SAR) and effective depths of heating patterns induced by a shortwave, pancake diathermy applicator in fat-muscle phantom are measured. Midplane partitions of polyethylene and silk screen with and without contact chemicals are used. Thermographically obtained SAR data show nearly the same value for silk-screen partitions with and without contact chemicals and slightly lower values with polyethylene partitions, provided that the partition midplanes are tightly pressed against each other. Thermometry data indicate that for low-power exposures the major error in thermographic measurements obtained after termination of heating is due to thermal diffusion and not evaporative cooling in the opened midplane of the phantom.     

Improved preferential tumor hyperthermia with regional heating and systemic blood cooling: a balanced heat transfer method

Absorption of power in large body volumes can occur with some approaches used for hyperthermia treatment of cancer. A systemic heat absorption rate exceeding the heat dissipation rate can lead to systemic temperature elevation that limits the magnitude and duration of application of power and hence the degree of preferential tumor temperature rise. We describe a hyperthermia approach consisting of regional electromagnetic power absorption and extracorporeal blood cooling with regulation of both systemic heat absorption and dissipation rates ("balanced heat transfer"). A test of this approach in five dogs with nonperfused tumor models demonstrated intratumoral temperatures greater than 42 degrees C, while systemic temperature remained at 33 degrees C and visceral temperatures within the heated region equilibrated between 33 and 42 degrees C. Solutions of the bioheat transfer equation were obtained for a simplified model with a tumor perfusion rate lower than surrounding normal tissue perfusion rate. In this model, the use of arterial blood temperatures less than 37 degrees C allowed higher power densities to be used, for given normal tissue temperatures, than when arterial temperature was greater than or equal to 37 degrees C. As a result, higher intratumoral temperatures were predicted. Control of arterial blood temperature using extracorporeal cooling may thus (1) limit systemic temperature rise produced by regional heating devices and (2) offer a means of improving intratumoral temperature elevations.     

Exposure of non‐target tissues in medical diathermy

With different prevalence in different regions, radio frequency (RF) electromagnetic fields (EMF) are widely used for therapeutic tissue heating. Although short‐wave diathermy (27.12 MHz) is the most popular treatment modality, quantitative data on patient's exposure have been lacking. By numerical simulation with the numerical anatomical model NORMAN, intracorporal distributions of specific absorption rates (SAR) were investigated for different treatment scenarios and applicators. Quantitative data are provided for exposures of target treatment areas as well as for vulnerable regions such as the eye lenses, central nervous system, and testes. Different applicators and distances were investigated. Capacitive and inductive applicators exhibit quite a different heating efficiency. It could be shown that for the same output power therapeutic heat deposition can vary by almost one order of magnitude. By mimicking therapist's practice to use patient's heat perception as an indicator for output power setting, numerical data were elaborated demonstrating that muscle tissue exposures may be several times higher for inductive than for capacitive applicators. Presented quantitative data serve as a guide for power adjustment preventing relevant overexposures without compromising therapy; they also provide a basis for estimating target tissue heat load and developing therapeutic guidelines. Bioelectromagnetics 31:12–19, 2010. © 2009 Wiley‐Liss, Inc.     

A network model of successive partitioning-limited solute diffusion through the stratum corneum

As the most exposed point of contact with the external environment, the skin is an important barrier to many chemical exposures, including medications, potentially toxic chemicals and cosmetics. Traditional dermal absorption models treat the stratum corneum lipids as a homogenous medium through which solutes diffuse according to Fick's first law of diffusion. This approach does not explain non-linear absorption and irregular distribution patterns within the stratum corneum lipids as observed in experimental data. A network model, based on successive partitioning-limited solute diffusion through the stratum corneum, where the lipid structure is represented by a large, sparse, and regular network where nodes have variable characteristics, offers an alternative, efficient, and flexible approach to dermal absorption modeling that simulates non-linear absorption data patterns. Four model versions are presented: two linear models, which have unlimited node capacities, and two non-linear models, which have limited node capacities. The non-linear model outputs produce absorption to dose relationships that can be best characterized quantitatively by using power equations, similar to the equations used to describe non-linear experimental data.     

Absence of a synergistic effect between moderate-power radio-frequency electromagnetic radiation and adriamycin on cell-cycle progression and sister-chromatid exchange.

In our laboratories we are conducting investigations of potential interactions between radio-frequency electromagnetic radiation (RFR) and chemicals that are toxic by different mechanisms to mammalian cells. The RFR is being tested at frequencies in the microwave range and at different power levels. We report here on the 1) ability of simultaneous RFR exposures to alter the distribution of cells in first and second mitoses from that after treatment by adriamycin alone, and 2) on the ability of simultaneous RFR exposure to alter the extent of sister chromatid exchanges (SCEs) induced by adriamycin alone. This chemical was selected because of its reported mechanism of action and because it is of interest in the treatment of cancer. In our studies, Chinese hamster ovary (CHO) cells were exposed for 2 h simultaneously to adriamycin and pulsed RFR at a frequency of 2,450 MHz and a specific absorption rate of 33.8 W/Kg. The maximal temperature (in the tissue-culture medium) was 39.7 +/- 0.2 degrees C. The experiments were controlled for chemical and RFR exposures, as well as for temperature. Verified statistically, the data indicate that the RFR did not affect changes in cell progression caused by adriamycin, and the RFR did not change the number of SCEs that were induced by the adriamycin, which adriamycin is known to affect cells by damaging their membranes and DNA.     

Predicting effects of blood flow rate and size of vessels in a vasculature on hyperthermia treatments using computer simulation

Background

Pennes Bio Heat Transfer Equation (PBHTE) has been widely used to approximate the overall temperature distribution in tissue using a perfusion parameter term in the equation during hyperthermia treatment. In the similar modeling, effective thermal conductivity (K_eff) model uses thermal conductivity as a parameter to predict temperatures. However the equations do not describe the thermal contribution of blood vessels. A countercurrent vascular network model which represents a more fundamental approach to modeling temperatures in tissue than do the generally used approximate equations such as the Pennes BHTE or effective thermal conductivity equations was presented in 1996. This type of model is capable of calculating the blood temperature in vessels and describing a vasculature in the tissue regions.

Methods

In this paper, a countercurrent blood vessel network (CBVN) model for calculating tissue temperatures has been developed for studying hyperthermia cancer treatment. We use a systematic approach to reveal the impact of a vasculature of blood vessels against a single vessel which most studies have presented. A vasculature illustrates branching vessels at the periphery of the tumor volume. The general trends present in this vascular model are similar to those shown for physiological systems in Green and Whitmore. The 3-D temperature distributions are obtained by solving the conduction equation in the tissue and the convective energy equation with specified Nusselt number in the vessels.

Results

This paper investigates effects of size of blood vessels in the CBVN model on total absorbed power in the treated region and blood flow rates (or perfusion rate) in the CBVN on temperature distributions during hyperthermia cancer treatment. Also, the same optimized power distribution during hyperthermia treatment is used to illustrate the differences between PBHTE and CBVN models. K_eff (effective thermal conductivity model) delivers the same difference as compared to the CBVN model. The optimization used here is adjusting power based on the local temperature in the treated region in an attempt to reach the ideal therapeutic temperature of 43°C. The scheme can be used (or adapted) in a non-invasive power supply application such as high-intensity focused ultrasound (HIFU). Results show that, for low perfusion rates in CBVN model vessels, impacts on tissue temperature becomes insignificant. Uniform temperature in the treated region is obtained.

Conclusion

Therefore, any method that could decrease or prevent blood flow rates into the tumorous region is recommended as a pre-process to hyperthermia cancer treatment. Second, the size of vessels in vasculatures does not significantly affect on total power consumption during hyperthermia therapy when the total blood flow rate is constant. It is about 0.8% decreasing in total optimized absorbed power in the heated region as γ (the ratio of diameters of successive vessel generations) increases from 0.6 to 0.7, or from 0.7 to 0.8, or from 0.8 to 0.9. Last, in hyperthermia treatments, when the heated region consists of thermally significant vessels, much of absorbed power is required to heat the region and (provided that finer spatial power deposition exists) to heat vessels which could lead to higher blood temperatures than tissue temperatures when modeled them using PBHTE.     

Millimeter wave absorption spectra of biological samples

A solid-state computer-controlled system has been used to make swept-frequency measurements of absorption of biological specimens from 26.5 to 90.0 GHz. A wide range of samples was used, including solutions of DNA and RNA, and suspensions of BHK-21/C13 cells, Candida albicans, C krusei, and Escherichia coli. Sharp spectra reported by other workers were not observed. The strong absorbance of water (10--30 dB/mm) caused the absorbance of all aqueous preparations that we examined to have a water-like dependence on frequency. Reduction of incident power (to below 1.0 microW), elimination of modulation, and control of temperature to assure cell viability were not found to significantly alter the water-dominated absorbance. Frozen samples of BHK-21/C13 cells tested at dry ice and liquid nitrogen temperatures were found to have average insertion loss reduced to 0.2 dB/cm but still showed no reproducible peaks that could be attributed to absorption spectra. It is concluded that the special resonances reported by others are likely to be in error.     

Electrical discontinuity of tissue substitute models at 27.12 MHz

Tissue-substitute models consisting of layers of synthetic, electrically equivalent subcutaneous fat, muscle, and bone shaped in conformation with the normal anatomy are used for rapid determination of distribution of temperature and specific absorption rate throughout the tissues when exposed to electromagnetic radiation. The surfaces of the bisected models are approximated during a short exposure period, then separated and scanned with a thermograph. A method was developed to eliminate the electrical discontinuity at the bisected surfaces while allowing separation and subsequent thermographic scanning. A thin layer of silk screen wetted with propylene glycol saturated with sodium chloride was used at the fat interface and a 0.9% sodium chloride solution was used to wet the screen at the muscle interface to eliminate electrical discontinuity during exposure to 27.12-MHz diathermy. Tests showed that in the presence of an electrical discontinuity the heating pattern was grossly distorted. With the method used, the electrical discontinuity is minimized and the subsequent thermographic scanning reveals that the heating pattern is equivalent to that of an intact model.     

RF Energy Absorption in Human Bodies Due to Wearable Antennas in the 2.4 GHz Frequency Band

Human exposure to electromagnetic fields produced by two wearable antennas operating in the 2.4 GHz frequency band was assessed by computational tools. Both antennas were designed to be attached to the skin, but they were intended for different applications. The first antenna was designed for off-body applications, i.e. to communicate with a device placed outside the body, while the second antenna model was optimized to communicate with a device located inside the body. The power absorption in human tissues was determined at several locations of adult male and female body models. The maximum specific absorption rate (SAR) value obtained with the off-body antenna was found on the torso of the woman model and was equal to 0.037 W/kg at 2.45 GHz. SAR levels increased significantly for the antenna transmitting inside the body. In this case, SAR values ranged between 0.23 and 0.45 W/kg at the same body location. The power absorbed in different body tissues and total power absorbed in the body were also calculated; the maximum total power absorbed was equal to 5.2 mW for an antenna input power equal to 10 mW. Bioelectromagnetics. 2020;41:73–79 © 2019 Wiley Periodicals, Inc.     

Exposure to non-ionizing radiation provokes changes in rat thyroid morphology and expression of HSP-90

Non-ionizing radiation at 2.45 GHz may modify the morphology and expression of genes that codify heat shock proteins (HSP) in the thyroid gland. Diathermy is the therapeutic application of non-ionizing radiation to humans for its beneficial effects in rheumatological and musculo-skeletal pain processes. We used a diathermy model on laboratory rats subjected to maximum exposure in the left front leg, in order to study the effects of radiation on the nearby thyroid tissue. Fifty-six rats were individually exposed once or repeatedly (10 times in two weeks) for 30 min to 2.45 GHz radiation in a commercial chamber at different non-thermal specific absorption rates (SARs), which were calculated using the finite difference time domain technique. We used immunohistochemistry methods to study the expression of HSP-90 and morphological changes in thyroid gland tissues. Ninety minutes after radiation with the highest SAR, the central and peripheral follicles presented increased size and the thickness of the peripheral septa had decreased. Twenty-four hours after radiation, only peripheral follicles radiated at 12 W were found to be smaller. Peripheral follicles increased in size with repeated exposure at 3 W power. Morphological changes in the thyroid tissue may indicate a glandular response to acute or repeated stress from radiation in the hypothalamic–pituitary–thyroid axis. Further research is needed to determine if the effect of this physical agent over time may cause disease in the human thyroid gland.     

Low power millimeter wave irradiation exerts no harmful effect on human keratinocytes in vitro

Low power millimeter wave (LP-MW) irradiation has been successfully used in clinical practice as an independent and/or supplemental therapy in patients with various diseases. It is still not clear, however, whether exposed skin is directly affected by repeated LP-MW irradiation and whether cells of the epidermis can be activated by the absorbed energy. Keratinocytes, the most numerous component of the epidermis are believed to manifest functional responses to physical stimuli. In this study we analyzed whether LP-MW irradiation modulated the production of chemokines, including RANTES and IP-10 of keratinocytes in vitro. We also investigated whether LP-MW irradiation induces a heat stress reaction in keratinocytes, and stimulates heat shock protein 70 (Hsp70) production. Vital staining of keratinocytes with carboxyfluorescein succinimidyl ester and ethidium bromide was used to analyze the MW effect on the viability of adherent cells. In addition, we studied the effect of LP-MW irradiation on intercellular gap junctional communication in keratinocyte monolayers by Lucifer yellow dye transfer. We found no significant changes in constitutive RANTES and inducible IP-10 production following LP-MW irradiation. LP-MW exposure of keratinocyte monolayers did not alter Hsp70 production, unlike exposure to higher power MWs (HP-MW) or hyperthermia (43 degrees C; 1 h). LP-MW irradiation and hyperthermia did not alter the viability of adherent keratinocytes, while HP-MW irradiation induced cellular damage within the beam area. Finally, we found no alteration in the gap junctional intercellular communication of keratinocytes following LP-MW irradiation, which on the other hand, was significantly increased by hyperthermia. In summary, we detected no harmful effect of LP-MW irradiation on both keratinocyte function and structure in vitro, although these cells were sensitive to higher MW power that developed heat stress reaction and cellular damage. Our results provide further evidence that LP-MW irradiation does not induce evidence of skin inflammation or keratinocyte damage and that its clinical application appears to be safe.     

Implanted Miniaturized Antenna for Brain Computer Interface Applications: Analysis and Design

Implantable Brain Computer Interfaces (BCIs) are designed to provide real-time control signals for prosthetic devices, study brain function, and/or restore sensory information lost as a result of injury or disease. Using Radio Frequency (RF) to wirelessly power a BCI could widely extend the number of applications and increase chronic in-vivo viability. However, due to the limited size and the electromagnetic loss of human brain tissues, implanted miniaturized antennas suffer low radiation efficiency. This work presents simulations, analysis and designs of implanted antennas for a wireless implantable RF-powered brain computer interface application. The results show that thin (on the order of 100 micrometers thickness) biocompatible insulating layers can significantly impact the antenna performance. The proper selection of the dielectric properties of the biocompatible insulating layers and the implantation position inside human brain tissues can facilitate efficient RF power reception by the implanted antenna. While the results show that the effects of the human head shape on implanted antenna performance is somewhat negligible, the constitutive properties of the brain tissues surrounding the implanted antenna can significantly impact the electrical characteristics (input impedance, and operational frequency) of the implanted antenna. Three miniaturized antenna designs are simulated and demonstrate that maximum RF power of up to 1.8 milli-Watts can be received at 2 GHz when the antenna implanted around the dura, without violating the Specific Absorption Rate (SAR) limits.     

Evaluation of the effectiveness of transurethral radio frequency hyperthermia in the canine prostate: temperature distribution analysis

The heating pattern of a transurethral radio frequency (RF) applicator and its induced steady-state temperature field in the prostate during transurethral hyperthermia treatment were investigated in this study. The specific absorption rate (SAR) of the electromagnetic energy was first quantified in a tissue-equivalent gel phantom. It was used in conjunction with the Pennes bioheat transfer equation to model the steady-state temperature field in prostate during the treatment. Theoretical predictions were compared to in vivo temperature measurements in the canine prostate and good agreement was found to validate the model. The prostatic tissue temperature rise and its relation to the effect of blood perfusion were analyzed. Blood perfusion is found to be an important factor for removal of heat especially at the higher RF heating level. To achieve a temperature above 44 degrees C within 10 percent of the prostatic tissue volume, the minimum RF power required ranges from 5.5 W to 36.4 W depending on the local blood perfusion rate (omega = 0.2-1.5 ml/gm/min). The corresponding histological results from the treatment suggest that to obtain better treatment results, either higher RF power level or longer treatment time (> 180 minutes) is necessary. This is consistent with the predictions from the theoretical model developed in this study.     

Use of diathermy for weeding heterogeneous tissue cultures

Summary Cultures generated from tissues consisting of multiple types of cells are often heterogeneous. Unless the cell type of interest has or can be given some selective growth advantage it may be overgrown by other cells. While developing techniques for the tissue culture of microvascular endothelial cells we evaluated an electrosurgical generator (diathermy) to selectively kill nonendothelail cells. Primary cell cultures were observed at ×100 magnification under phase contrast microscopy and a needle electrode apposed to the cell to be destroyed. A return electrode was constructed by placing a sterile clip in contact with the culture medium. The diathermy power setting controlled the area of lysis. Use of this technique allowed weeding of unwanted cells without damage to endothelial cells, which were able to grow to confluence in pure culture. Dr. Marks receives a Medical Postgraduate Research Scholarship from the National Health and Medical Research Council of Australia. Financial support was received from the Leo Leukaemia and Cancer Research Trust and the Scleroderma Association of New South Wales.     

螺旋藻培养液吸收CO2特性的研究

培养液中含有高浓度的ＨＣＯ和ＣＯ,活跃进行的ＣＯ２,ＨＣＯ和ＣＯ３种碳源形式相互转变的化学反应,构成了螺旋藻培养液不同于其它藻类培养液的显著特征。定量研究了ＣＯ２吸收速率与碳源浓度、温度、ｐＨ值、盐度、培养液运动状态的关系,利用培养液吸收ＣＯ２的物理模型解释了碳源浓度、ｐＨ值、培养液运动状态影响ＣＯ２吸收速率的机理。对化学反应是否影响ＣＯ２吸收速率这一有争议的问题进行了探讨,在肯定化学反应影响的前提下,指出化学反应的影响能否被观察到,显著程度如何,关键在于培养液的运动状态。根据实验结果,给出了利用“气罩法”添加ＣＯ２,所需气罩面积与产量、碳源浓度、培养液运动状态、培养面积数量关系的理论值。使用培养液的“ＣＯ２容量”的概念,说明利用ＣＯ２为碳源培养螺旋藻与其它藻类相比,可以得到更高的碳源利用率,从而产生更大的效益。     

Nonlinear changes in brain electrical activity due to cell phone radiation

We studied the effect of an electromagnetic field from a cellular telephone on brain electrical activity, using a novel analytical method based on a nonlinear model. The electroencephalogram (EEG) from rabbits was embedded in phase space and local recurrence plots were calculated and quantified using recurrence quantitation analysis to permit statistical comparisons between filtered segments of exposed and control epochs from individual rabbits. When the rabbits were exposed to the radiation from a standard cellular telephone (800 MHz band, 600 mW maximum radiated power) under conditions that simulated normal human use, the EEG was significantly affected in nine of ten animals studied. The effect occurred beginning about 100 ms after initiation of application of the field and lasted approximately 300 ms. In each case, the fields increased the randomness in the EEG. A control procedure ruled out the possibility that the observations were a product of the method of analysis. No differences were found between exposed and control epochs in any animal when the experiment was repeated after the rabbits had been sacrificed, indicating that absorption of radiation by the EEG electrodes could not account for the observed effect. No effect was seen when deposition of energy in the brain was minimized by repositioning the radiating antenna from the head to the chest, showing that the type of tissue that absorbed the energy determined the observed changes in the EEG. We conclude that, in normal use, the fields from a standard cellular telephone can alter brain function as a consequence of absorption of energy by the brain.     

The Importance of Subcellular Structures to the Modeling of Biological Cells in the Context of Computational Bioelectromagnetics Simulations

Numerical investigation of the interaction of electromagnetic fields with eukaryotic cells requires specifically adapted computer models. Virtual microdosimetry, used to investigate exposure, requires volumetric cell models, which are numerically challenging. For this reason, a method is presented here to determine the current and volumetric loss densities occurring in single cells and their distinct compartments in a spatially accurate manner as a first step toward multicellular models within the microstructure of tissue layers. To achieve this, 3D models of the electromagnetic exposure of generic eukaryotic cells of different shape (i.e. spherical and ellipsoidal) and internal complexity (i.e. different organelles) are performed in a virtual, finite element method-based capacitor experiment in the frequency range from 10 Hz to 100 GHz. In this context, the spectral response of the current and loss distribution within the cell compartments is investigated and any effects that occur are attributed either to the dispersive material properties of these compartments or to the geometric characteristics of the cell model investigated in each case. In these investigations, the cell is represented as an anisotropic body with an internal distributed membrane system of low conductivity that mimics the endoplasmic reticulum in a simplified manner. This will be used to determine which details of the cell interior need to be modeled, how the electric field and the current density will be distributed in this region, and where the electromagnetic energy is absorbed in the microstructure regarding electromagnetic microdosimetry. Results show that for 5 G frequencies, membranes make a significant contribution to the absorption losses. © 2023 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.     

An analytical solution for percutaneous drug absorption: application and removal of the vehicle

The methods of Laplace transform were used to solve a mathematical model developed for percutaneous drug absorption. This model includes application and removal of the vehicle from the skin. A system of two linear partial differential equations was solved for the application period. The concentration of the medicinal agent in the skin at the end of the application period was used as the initial condition to determine the distribution of the drug in the skin following instantaneous removal of the vehicle. The influences of the diffusion and partition coefficients, clearance factor and vehicle layer thickness on the amount of drug in the vehicle and the skin were discussed.