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Electromagnetic power absorption in biological tissues has recently received due scientific and public attention, particularly, in the areas of cellular communication and hyperthermic treatments. While efficient numerical algorithms, such as the finite difference time domain technique and the method of moments, have been developed as to obtain accurate power distributions in complicated configurations, their physical interpretation and explicit dependence on problem’s parameters are still difficult to achieve. In attempt to gain a clear insight into the electromagnetic power absorption mechanism as well as its estimation and relation to the Specific Absorption Rate (SAR), we have recently proposed an infinite-extent current-sheet model. Herein, the model is further extended by incorporating finite-extent sources, i.e., electric and magnetic line-sources, exciting a highly lossy semi-infinite half-space. This modification results in deeper insight and understanding of the crucially important parameters, commonly involved in realistic configurations, namely, bounds and estimates on the power absorption and radiation efficiencies, local and total SAR coupling coefficients, and effective absorption dimensions. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The phenomenon of electromagnetic power absorption in biological tissues has recently become of increased scientific and public interest, particularly in the areas of cellular communication and hyperthermia systems. Electromagnetic power absorption in biological tissues is a well-known phenomenon. Its evaluation requires, in general, a solution of the three-dimensional frequency-dependent wave equation in complex configurations, which may necessitate quite massive analytical and numerical efforts. Herein, we focus on an elementary plane-wave model. The model establishes a tight estimate on the optimal (maximal/minimal) power absorption in realistic microwave configurations, in particular, cellular communications safety assessments. Furthermore, the absorption efficiency as well as the source impedance are obtained via explicit closed-form expressions, leading to an explicit maximal power absorption criterion for highly lossy tissues. The results depend continuously and explicitly on the physical parameters of biological tissues as well as on the plane-wave incidence angle and excitation source location. They are shown to be closely related to electromagnetic specific absorption rate estimations in biological tissues. In view of the well-known analogy between plane waves and rectangular waveguide modes, our results can be applied to optimization schemes of microwave heating and waveguide based therapeutic hyperthermia systems. [ABSTRACT FROM AUTHOR]

Semiconductor γ-ray spectrometer devices, which possess attractive properties over alternative devices (e.g., scintillators), have received due attention recently. Evidently, efficient and accurate modeling of these devices, in particular, of the induced charges and internal fields, is crucially important for further development and engineering implementation. Previous attempts to analyze the spectrometers were either oversimplified, i.e., Image Charges (IC) in an idealized infinite parallel plate capacitor, or time consuming, utilizing a Point Charge Moment Method (PCMM) scheme. While the first attempt results in poor accuracy, the second leads to an enhanced accuracy but with the cost of large computation time. Thus, it is desirable to develop a modeling technique that is capable of generating both accurate and efficient solutions. An attempt in this direction is outlined in our work, which introduces the Fourier Series Expansion (FSE) scheme. The model utilizes the eigenfunctions of an idealized infinite two-dimensional array of anodes, namely, Fourier harmonics. These base functions exhibit an accurate and fast converging solution. Thus, it can be effectively applied for practical (finite) devices as long as edge effects can be neglected. This constraint is generally satisfied in practical devices, since the device contains a large number of anodes and the detectable photogenerated carriers are located sufficiently far from the device edges. Numerical comparison of the FSE scheme with the PCMM and IC techniques reveals the effectiveness and usefulness of the proposed scheme. While the FSE and PCMM techniques agree within 2%, the agreement with the IC method is within 7%, as expected. [ABSTRACT FROM AUTHOR]

Traditionally, surface plasmon resonance (SPR) biosensors utilize absorption of light radiation incident upon noble metal films above the total internal reflection angles. Herein we extend the SPR phenomenon to incorporate cavity plasmon resonance (CPR) excitation of metallic films at incidence angles below the critical angle. While SPR occurs for TM polarized light only and requires very specific excitation conditions, which could be disadvantageous in some practical designs, CPR does not require complicated evanescent field excitation above the critical total internal reflection angle and can be implemented for both transverse electric (TE) and transverse magnetic (TM) fields even under normal incidence (TEM). These and other unique features of CPR enable a more flexible design of highly efficient and sensitive biosensing devices.

A novel electrical impedance tomography method is introduced for reconstruction of layered biological tissues with continuous plane-stratification. The algorithm implements the recently proposed reconstruction scheme for piecewise constant conductivity profiles, based on an improved Prony method in conjunction with Legendre polynomial expansion (LPE). It is shown that the proposed algorithm is capable of successfully reconstructing continuous conductivity profiles with moderate (WKB) slop. Features of the presented reconstruction scheme include, an inherent linearity, achieved by the linear LPE transform, a locality feature, assigning analytically to each spectral component a local electrical impedance associated with a unique location, and effective performance even in the presence of noisy measurements.

A novel electrical impedance tomography method is introduced for reconstruction of layered biological tissues. The method utilizes a recently proposed image series expansion scheme in conjunction with the WKB approximation. This results in a locality feature, assigning analytically to each image term a local impedance associated with a unique layer, and thus leading to linear, efficient, and accurate reconstruction procedures.

A novel electrical impedance tomography method is introduced for reconstruction of layered biological tissues. The method utilizes a recently proposed image series expansion scheme in conjunction with the WKB approximation. This results in a locality feature, assigning analytically to each image term a local impedance associated with a unique layer, and thus leading to efficient and accurate reconstruction procedures.

By analyzing and optimizing acoustic and electromagnetic waves absorption in a simplified layered model of hyperthermic configuration, it is shown that the commonly used attenuation metrics are not always proper means for determining the generally optimal parameters of typical thermal therapy problem with finite extent target The conditions, parameters and bounds for optimal (maximal) incident power absorption for the layered model have been found analytically and explicitly and are presented in terms of basic wave propagation characteristics, thus, also providing the necessary data for optimal synthesis of absorbing tissues and materials.

A hybrid scheme, combining image series and moment method has been utilized for the calculation of the intramuscular three-dimensional (3-D) current density (CD) distribution and potential field transcutaneously excited by an electrode array. The model permits one to study the effect of tissue electrical properties and electrode placement on the CD distribution. The isometric recruitment curve (IRC) of the muscle was used for parameter estimation and model verification, by comparison with experimentally obtained IRCs of functional electrical stimulation (FES)-activated quadriceps muscle of paraplegic subjects. Sensitivity of the calculated IRC to parameters such as tissue conductivity, electrode size, and configuration was verified. The resulting model demonstrated characteristic features that were similar to those of experimentally obtained data. The model IRCs were insensitive to the electrode size; however, the inclusion of the bone-fascia layer significantly increased the intramuscular CD and, consequently, increased the IRC slope. Of the different configurations studied, a four-electrode array proved advantageous because, in this case, the CD between the electrodes was more evenly distributed, providing better resistance to fatigue. However, due to the steeper linear portion of the IRC, this configuration suffered from a somewhat reduced controllability of the muscle.