Numerical Dosimetry Research Articles

A new in vitro exposure device for the mobile frequency of 900 MHz.

A wire patch cell has been designed for exposing cell cultures during in vitro experiments studying possible effects of mobile radio telephone. It is based on the wire patch antenna which works at 900 MHz with a highly homogeneous field inside the antenna cavity. The designed cell structure is symmetric and provides a rather homogeneous field distribution in a large area around its centre. Moreover, the exposure cell can irradiate equally up to eight 35 mm Petri dishes at the same time, which enhances the statistical biological studies. To improve the specific absorption rate (SAR) homogeneity inside each sample, each dish is placed into another 50 mm dish. This way, SAR inhomogeneity is always proper for biological studies (below 30%). The main advantage of this new device is that it can provide SAR levels 20 times higher than those induced by classical Crawford transverse electromagnetic (TEM) cell. Moreover, this small open device is easy to construct and fits into an incubator. However, to be used for in vitro, the wire patch cell is a radiating element with the same radiating pattern as a dipole, and thus some absorbing materials are necessary around the system when used for in vitro experiments. Secondly, because of its narrow bandwidth, it is difficult to maintain its working frequency. To overcome this problem, a matching device is integrated into the test cell. In this paper, we present a detailed explanation of the cell behavior and dosimetric assessments for eight 35 mm Petri dishes exposed. Simulations using the Finite Difference Time Domain technique and experimental investigations have been carried out to design the cell at 900 MHz. The numerical dosimetry was validated by dosimetric measurements. These investigations estimated the dosimetric precision at 11%.

Design, optimization, realization, and analysis of an in vitro system for the exposure of embryonic stem cells at 1.71 GHz

The aim of this study was to develop an exposure system which enables in vitro experiments to be conducted under variously modulated radiofrequency exposures. Based on the evaluation of different possible systems, it was decided to realize a system based on rectangular waveguides. The system was optimized for the following parameters: (1) homogeneity of the cell exposure, (2) simultaneous exposure of several Petri dishes, (3) efficiency, (4) strict environmental control, (5) quick and easy access to the Petri dishes, (6) cost, and (7) simple operation by non-engineering personnel. The implemented control software enables investigation of a wide spectrum of amplitude modulation schemes between 0.1 Hz and 1 kHz, including the modulation schemes of current and future digital mobile communication systems as well as other exposure protocols. The system described has been initially utilized for a study on the differentiation and cell functions of embryonic stem cells. Detailed numerical and experimental dosimetry and environmental tests have demonstrated that it meets all target objectives. The entire system including the sham exposure system fits into a single incubator. It enables the carrying out of various experiments designed to test biological responses to RF exposures at 1.2-1.7 GHz by using various modulation schemes and long term exposure protocols as well as simultaneous data logging.

Rapporteur Report: Sources and Exposure Metrics for RF Epidemiology (Part 1)

A variety of sources was considered, illustrating the predominantly uniform exposure at a distance and highly nonuniform exposures close to sources. The measurement of both electric and magnetic fields was considered for near field situations hut where possible the use of induced body currents was judged to be the preferred metric. The salient features affecting exposure to fields from mobile telephones and their base stations were discussed for both existing and third generation systems. As an aid to future cancer studies, high resolution numerical modelling was used to illustrate left/right exposure discrimination of hilateral organs in the head. Factors influencing both numerical and experimental dosimetry were discussed and studies to investigate the ahility to appropriately rank exposure were considered important areas for research.

High-resolution magnetic field numerical dosimetry for live-line workers

Numerical modeling provides one means for the realistic assessment of the electric field and current density levels induced in the bodies of live-line utility workers during occupational exposure to 60 Hz nonuniform magnetic fields. An efficient scalar potential finite difference method is applied to anatomically-derived high-resolution heterogeneous human body conductivity models, to provide such estimates for four representative posture and exposure scenarios. Dosimetric data are presented in terms of volumetric maximum and root mean square fields induced in various tissue groups by unit current. The results scale linearly with total source current, which allows the data to be applied to arbitrary current levels.

Localized specific absorption rate calculations in a realistic phantom leg at 1-30 MHz using a finite element method

Protection standards for radiofrequency electromagnetic radiation are principally intended to avoid detrimental thermal effects. To this end the International Commission on Non-Ionizing Radiation Protection (ICNIRP), and national bodies such as the National Radiological Protection Board (NRPB), recommend limitations on the localized specific energy absorption rate (SAR) in various parts of the body. The role of numerical dosimetry is to estimate the SAR from measurable parameters such as external field strengths and total body currents. In recent years there have been significant advances in the sophistication of the anatomical models available, and in our knowledge of the electrical properties of the body tissues. Several groups, including NRPB, have developed mathematical phantoms from medical imaging data, such as MRI scans. It has been known for some time that under certain circumstances SAR restrictions may be violated in the ankle due to the concentration of current in a small area. In this paper the author presents calculations of the SAR distribution in a human leg in the high-frequency (HF) band. This band contains the human whole-body resonance frequency and therefore gives the strongest coupling of the body to the field. The present study uses a finite element model with variable mesh size, derived from a 2 mm resolution voxel phantom of the whole body. It also uses recently acquired data on the electrical properties of the tissues. The results are discussed in the light of the exposure standards promulgated by national and international bodies such as NRPB and ICNIRP, and it is shown that the basic SAR restrictions in the leg are ensured by a current reference level of 100 mA.

The 1.5 GHz electromagnetic near-field used for cellular phones does not promote rat liver carcinogenesis in a medium-term liver bioassay.

We have recently established that local exposure to a 929.2 MHz electromagnetic near‐field, used for cellular phones, does not promote rat liver carcinogenesis in a medium‐term bioassay system. In the present study, a 1.439 GHz electromagnetic near‐field (EMF), another microwave band employed for cellular phones in Japan, was similarly investigated. Time division multiple access (TDMA) signals for the Personal Digital Cellular (PDC) Japanese cellular telephone standard system were directed to rats through a quarter‐wavelength monopole antenna. Numerical dosimetry showed that the peak SARs within the liver were 1.91–0.937 W/kg, while the whole‐body average specific absorption rates (SARs) were 0.680–0.453 W/kg, when the time‐averaged antenna radiation power was 0.33 W. Exposure was for 90 min a day, 5 days a week, over 6 weeks, to male F344 rats given a single dose of diethylnitrosamine (200 mg/kg, i.p.) 2 weeks previously. At week 3, all rats were subjected to a two‐thirds partial hepatectomy. At week 8, the experiment was terminated and the animals were killed. Carcinogenic potential was scored by comparing the numbers and areas of the induced glutathione S‐transferase placental form (GST‐P)‐positive foci in the livers of exposed (48) and sham‐exposed rats (48). Despite increased serum levels of corticosterone, adrenocorticotropic hormone (ACTH) and melatonin, the numbers and the areas of GST‐P‐positive foci were not significantly altered by the exposure. These findings clearly indicated that local body exposure to a 1.439 GHz EMF, as in the case of a 929.2 MHz field, has no promoting effect on rat liver carcinogenesis in the present model.

Reference Fluence-to-Dose-Equivalent Conversion Coefficients and Angular Dependence Factors for 4-Element ICRU Tissue, Water and PMMA Slab Phantoms Irradiated by Broad Electron Beams

In order to support a Joint ICRP/ICRU Task Group action aiming at the collection of data of interest in the field of radiation protection, the EURADOS Working Group 4 'Numerical Dosimetry' has initiated a computational programme for the determination of fluence-to-absorbed-dose or dose-equivalent conversion coefficients for slab phantoms irradiated by external electrons of normal and oblique incidence. Seven experts in electron transport simulations agreed to contribute to the project. Using different code systems, they provided new data in the energy range between 60 keV and 10 MeV for three slab phantoms consisting of 4-element ICRU tissue, water and PMMA, at depths of 0.007 g.cm -2 , 0.3 g.cm -2 and 1.0 g.cm -2 . From those data, reference conversion coefficients were derived for each depth. This paper summarises the main features of the detailed data analysis subsequently performed on the different sets of numerical values, and extensively described in PTB Report Dos-24.

Numerical and experimental dosimetry of petri dish exposure setups

Numerical and experimental dosimetry of petri dish exposure setups

Numerical and experimental dosimetry of petri dish exposure setups

Numerical and experimental dosimetry of petri dish exposure setups

Numerical and experimental dosimetry of Petri dish exposure setups.

Crawford TEM cells are often used to expose cell cultures or small animals in order to study the effects caused by high-frequency fields. They are self-contained, easy-to-use setups that provide a rather homogeneous field distribution in a large area around its center, corresponding approximately to far-field conditions. However, a number of conditions must be met if such TEM cells are intended to be used for in vitro experiments. For instance, poor interaction with the incident field must be maintained to avoid significant field disturbances in the TEM cell. This is best achieved with E-polarization, i.e., when the E-field vector is normal to the investigated cell layer lining the bottom of a synthetic Petri dish. In addition, E-polarization provides the most homogeneous field distribution of all polarizations within the entire layer of cells. In this paper, we present a detailed dosimetric assessment for 60 and 100 mm Petri dishes as well as for a 48-well titer plate at 835 MHz. The dosimetry was performed by using numerical computations. The modeling and the simplifications are validated by a second numerical technique and by experimental measurements. For thin liquid layers, an approximation formula is provided with which the induced field strength for many other experiments conducted in Petri dishes can be assessed reliably.

Numerical dosimetry at power-line frequencies using anatomically based models.

We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function of height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively.

Diagnostic film dosimeter in the study of radiation exposure to the population resulting from x-ray fluoroscopy.

Abstract With the diagnostic film dosimeter developed by themselves, authors obtained satisfactory information about the radiation exposure and scrotal dose of about 2,700 patients subjected to chest fluoroscopy. The survey data offer valuable numerical dosimetry values and at the same time information about dose distribution and fluoroscopic methodology and aperture.