Performance comparison of available interstitial antennas formicrowave hyperthermia

The authors have developed a numerical model which calculates the current distribution and radiation characteristics of multisection antennas have varying diameters of the center conductor and/or the types and thicknesses of the insulation. They briefly describe the model and compare the numerical results with the experimental data published by T.P. Ryan and J.W. Strohbehn (1987). Excellent correlation between the experimental and calculated patterns was obtained. The numerical model was then used to examine some interesting changes in the commercial designs, such as the effect of the tip termination of the antenna and the diameters of the conducting sections (collars) on the heating patterns of the BSD Medical antenna. Important observations regarding the role of each section, in multisection antenna designs, in guiding along the antenna vs. coupling to the ambient were also investigated and verified     

Estimation of temperature distribution inside tissues heated byinterstitial RF electrode hyperthermia systems

The computational method presented relies on a semi-infinite tissue model. The needle-shaped RF electrodes are modeled with elongated spheroids. The heat transfer problem is treated in three dimensions. The localized current fields set up inside the tissue from the discrete implants are computed by using electrostatic methods, and the bioheat diffusion equation under a steady-state condition is solved to determine the temperature distributions inside superficial tissues. A Green's-function technique is applied to solve the bioheat transfer equation. The heat removal due to blood circulation is also taken into account. Analytical techniques are used to treat the singularities in the vicinity of implanted electrodes. Numerical results are presented for several electrode configurations     

A dipole antenna for interstitial microwave hyperthermia

An improved interstitial microwave antenna design was investigated in static phantom experiments at 915 MHz and different insertion depths. Compared with conventional interstitial antennas, the presented dipole microwave antenna shows heating patterns which are concentrated on the dipole irrespective of the insertion depth. By analogy to interstitial radiotherapy, the microwave antenna allows a high concentration of energy in the target volume with as little damage as possible to the healthy surrounding tissue. The undesired heating of healthy tissue along the feeding line observed with conventional interstitial antennas is avoided. A λ/4 sleeve on the feeding line (which does not radiate microwave energy itself to the surrounding tissue) transforms an open end, i.e. a high impedance at the generator end of the dipole antenna. The current flowing back along the outside of the outer conductor of the feeding line in the direction of the generator is zero at this point. Both dipole sections have the same terminating impedance. Since the λ/4 sleeve is mounted outside the antenna, its mechanical length is not restricted by the mechanical length of the antenna. It can be charged with dielectric materials of low dielectricity constants     

A perfused tissue phantom for ultrasound hyperthermia

A perfused tissue phantom, developed as a tool for analyzing the performance of ultrasound hyperthermia applicators, was investigated. The phantom, consisting of a fixed porcine kidney with thermocouples placed throughout the tissue, was perfused with degassed water by a variable flow rate pump. The phantom was insonated by an unfocused multielement ultrasound applicator and the temperatures in the phantom were recorded. The results indicate that for testing protocols where tissue phantoms are needed, the fixed kidney preparation offers an opportunity to use a more realistic phantom than has previously been available to assess the heating performance of ultrasound hyperthermia applicators.     

A comparison of the effects of electrode implantation and targeting on pattern classification accuracy for prosthesis control

The use of surface versus intramuscular electrodes as well as the effect of electrode targeting on pattern-recognition-based multifunctional prosthesis control was explored. Surface electrodes are touted for their ability to record activity from relatively large portions of muscle tissue. Intramuscular electromyograms (EMGs) can provide focal recordings from deep muscles of the forearm and independent signals relatively free of crosstalk. However, little work has been done to compare the two. Additionally, while previous investigations have either targeted electrodes to specific muscles or used untargeted (symmetric) electrode arrays, no work has compared these approaches to determine if one is superior. The classification accuracies of pattern-recognition-based classifiers utilizing surface and intramuscular as well as targeted and untargeted electrodes were compared across 11 subjects. A repeated-measures analysis of variance revealed that when only EMG amplitude information was used from all available EMG channels, the targeted surface, targeted intramuscular, and untargeted surface electrodes produced similar classification accuracies while the untargeted intramuscular electrodes produced significantly lower accuracies. However, no statistical differences were observed between any of the electrode conditions when additional features were extracted from the EMG signal. It was concluded that the choice of electrode should be driven by clinical factors, such as signal robustness/stability, cost, etc., instead of by classification accuracy.     

A comparison study of electrode material effects on the molecular single electron transistor

In this paper, the studies of Molecular Single electron Transistor (MSET) is presented. We have used the Extended Huckel Theory (EHT) coupled with non-equilibrium green's function (NEGF) formalism which is implemented in ATOMISTIC TOOLKIT package. The transport properties with different electrode materials have been studied for the first time using pentacene molecule. The presence of Coulomb blockade on I–V characteristics confirmed that our device operates as Single Electron Transistor. The negative differential resistance (NDR) effect and the coulomb Staircase state has been outlined. The transmission Spectra and density of states (DOS) dependence of the electrode has also been explored to analyze the I-V curves. The NDR behavior and size device make our MSET as a good candidate for use in gate logic circuit with low consumption.     

A framework of architectural concepts for high-speed communicationsystems

A framework for understanding high-speed communication architectures and protocols is presented. The framework is validated by showing how several concepts fit into it. Two approaches to reduce the number of processing operations required for a single datum, the reduction of control processing and the elimination of unneeded or replicated operations, are discussed. Two other approaches for increasing communication system speed by performing more processing operations per unit time, parallel processing and increased processor utilization, are also discussed     

A clinical water-coated antenna applicator for MR-controlled deep-body hyperthermia: a comparison of calculated and measured 3-D temperature data sets

A magnetic resonance (MR)-compatible three-dimensional (3-D) hyperthermia applicator was developed and evaluated in the magnetic resonance (MR) tomograph Siemens MAGNETOM Symphony 1.5 T. Radiating elements of this applicator are 12 so-called water coated antenna (WACOA) modules, which are designed as specially shaped and adjustable dipole structures in hermetically closed cassettes that are filled by deionized water. The WACOA modules are arranged in the applicator frame in two transversal antenna subarrays, six antennas per subarray. As a standard load for the applicator an inhomogeneous phantom was fabricated. Details of applicator's realization are presented and a 3-D comparison of calculated and measured temperature data sets is made. A fair agreement is achieved that demonstrates the numerically supported applicator's ability of phase-defined 3-D pattern steering. Further refinement of numerical models and measuring methods is necessary. The applicator's design and the E-field calculations were performed using the finite-difference time-domain (FDTD) method. The calculation and optimization of temperature patterns was obtained using the finite element method (FEM). For MR temperature measurements the proton resonance frequency (PRF) method was used.     

A spherical-section ultrasound phased array applicator for deeplocalized hyperthermia

Computer simulation shows that a new ultrasound phased-array with nonplanar geometry has considerable potential as an applicator for deep localized hyperthermia. The array provides precise control over the heating pattern in three dimensions. The array elements form a rectangular lattice on a section of a sphere. Therefore, the array has a natural focus at its geometric center when all its elements are driven in phase. When compared to a planar array with similar dimensions, the spherical-section array provides higher focal intensity gain which is useful for deep penetration and heat localization. Furthermore, the relative grating-lobe level (with respect to the focus) is lower for scanned foci synthesized with this array (compared to a planar array with equal center-to-center spacing and number of elements). This could be the key to the realization of phased-array applicator systems with a realistic number of elements. The spherical-section array is simulated as a spot-scanning applicator and, using the pseudo-inverse pattern synthesis method, to directly synthesize heating patterns overlaying the tumor geometry. A combination of the above two methods can be used to achieve the desired heating pattern in the rapidly varying tumor environment.     

A sampling theorem for EEG electrode configuration

An analytical tool to help in selecting the number of electrodes required for recording electroencephalogram (EEG) signals is presented. The main assumption made is that the scalp can be modeled as a hemispherical surface. The number of sensors required to sample a surface is derived by using a mean square error (MSE) measure to approximate the continuous potential functions on the hemispherical surface. An algorithm for selecting the number of electrodes for arbitrary head geometries is also proposed. A sampling theorem is then derived with conditions on the sampling points for electrode placement     

A 3-D SAR model for current source interstitial hyperthermia

A three-dimensional (3-D) model is presented for the calculation of the specific absorption rate (SAR) in human tissue during current source interstitial hyperthermia. The model is capable of millimeter resolution and can cope with irregular implants in heterogeneous tissue. The SAR distribution is calculated from the electrical potential. The potential distribution is determined by the dielectric properties of the tissue and by the electrode configuration. The dielectric properties and the current injection of the electrodes are represented on a 3-D uniform grid. The calculated potential at an electrode current injection point is not the actual electrode potential at that point. To estimate this potential a grid independent representation of an electrode together with an analytical solution in the neighborhood of the electrode are used. The calculated potential on the electrode surface is used to estimate the electrode impedance. The tissue implementation is validated by comparing calculated distributions with analytical solutions. The electrode implementation is verified by comparing different discretizations of an electrode configuration and by comparing numerically calculated electrode impedances with analytically calculated impedances     

He—Ne激光照射小鼠睾丸的光镜和电镜观察

以二种剂量的Ｈｅ－Ｎｅ激光分别照射二组雄性小鼠的阴囊，取睾丸组织作光镜和电镜观察。实验所用激光剂量分别为临床常用最大剂量的２０倍和７５倍。实验结果表明，实验动物生精上皮无紊乱和松散现象，各级生精细胞，成熟精子，支持细胞及睾丸间质细胞和超微结构无明显损伤。     

A novel dry active electrode for EEG recording

The design and testing of a "dry" active electrode for electroencephalographic recording is described. A comparative study between the EEG signals recorded in human volunteers simultaneously with the classical Ag-AgCl and "dry" active electrodes was carried out and the reported preliminary results are consistent with a better performance of these devices over the conventional Ag-AgCl electrodes.     

A real-time prediction model of electrode extension for GMAW

This paper presents the development of an electrode extension model for the gas metal arc welding process based on the process voltage. The full dynamic model for the electrode extension is derived by combining a dynamic resistivity model with the voltage model. The electrode extension model was found to be represented mathematically by a nonlinear, time-varying, second-order ordinary differential equation. This model can be used in through-the-arc sensing and arc length control systems. To experimentally verify the model, the process dynamics were excited by a continuous sinusoidal variation of arc current. Using a constant current power source with the electrode positive, sinusoidal perturbations of variable amplitude were superimposed on the current to allow direct measurement of changes in electrode extension, arc length, and total voltage. A high-speed video system was used to capture the experimental electrode extension dynamics. The model was verified by comparing the frequency response of the model to the frequency response of the real process. Agreement between the simulations and the experimental results was found to be very good. The accuracy of this model was found to be approximately /spl plusmn/0.6 mm, which is considered to be suitable for process control applications.     

A micromachined silicon sieve electrode for nerve regenerationapplications

A micromachined silicon sieve electrode has been developed and fabricated to record from and stimulate axons/fibers of the peripheral nervous system by utilizing the nerve regeneration principle. The electrode consists of a 15-μm-thick silicon support rim, a 4-μm-thick diaphragm containing different size holes to allow nerve regeneration, thin-film iridium recording/stimulating sites, and an integrated silicon ribbon cable, all fabricated using boron etch-step and silicon micromachining techniques. The thin diaphragm is patterned using reactive ion etching to obtain different size holes with diameters as small as 1 μm and center-center spacings as small as 10 μm. The holes are surrounded by 100-200 μm² anodized iridium oxide sites, which can be used for both recording and stimulation. These sites have impedances of less than 100 kΩ @ 1 kHz and charge delivery capacities in the 4-6 mC/cm² range. The fabrication process is single-sided, has high yield, requires only five masks, and is compatible with integrated multilead silicon ribbon cables. The electrodes were implanted between the cut ends of peripheral taste fibers of rats (glossopharyngeal nerve), and axons functionally regenerated through holes, responding to chemical, mechanical, and thermal stimuli     

Reduced-order modeling for hyperthermia control

This paper analyzes the feasibility of using reduced-order modeling techniques in the design of multiple-input, multiple-output (MIMO) hyperthermia temperature controllers. State space thermal models are created based upon a finite difference expansion of the bioheat transfer equation model of a scanned focused ultrasound system (SFUS). These thermal state space models are reduced using the balanced realization technique, and an order reduction criterion is tabulated. Results show that a drastic reduction in model dimension can be achieved using the balanced realization. The reduced-order model is then used to design a reduced-order optimal servomechanism controller for a two-scan input, two thermocouple output tissue model. In addition, a full-order optimal servomechanism controller is designed for comparison and validation purposes. These two controllers are applied to a variety of perturbed tissue thermal models to test the robust nature of the reduced-order controller. A comparison of the two controllers validates the use of open-loop balanced reduced-order models in the design of MIMO hyperthermia controllers.     

A freshman engineering concepts course

A college-level modification of the Engineering Concepts Curriculum Project (ECCP) course, "The Man Made World," is described, and its use as a framework for a computer-communication based education system is suggested.     

Equalization concepts for EDGE

An equalization concept for the novel radio access scheme Enhanced Data rates for GSM Evolution (EDGE) is proposed by which high performance can be obtained at moderate computational complexity. Because high-level modulation is employed in EDGE, optimum equalization as usually performed in Global System for Mobile Communications (GSM) receivers is too complex and suboptimum schemes have to be considered. It is shown that delayed decision-feedback sequence estimation (DDFSE) and reduced-state sequence estimation (RSSE) are promising candidates. For various channel profiles, approximations for the bit error rate of these suboptimum equalization techniques are given and compared with simulation results for DDFSE. It turns out that a discrete-time prefilter creating a minimum-phase overall impulse response is indispensable for a favorable tradeoff between performance and complexity. Additionally, the influence of channel estimation and of the receiver input filter is investigated and the reasons for performance degradation compared to the additive white Gaussian noise channel are indicated. Finally, the overall system performance attainable with the proposed equalization concept is determined for transmission with channel coding     

A nitride-isolated molybdenum-polysilicon gate electrode for MOS VLSI circuits

A new gate electrode structure is demonstrated. The low-resistive gate electrode consists of a triple layer of molybdenum and polysilicon films isolated with an ultrathin silicon-nitride film, namely MTP-metal/tunneling nitride/polysilicon. The tunneling nitride, which is grown by direct thermal nitridation of silicon, avoids silicidation of molybdenum and diffusion of impurities resulting in a thin SiO2film of good quality. Characteristics of discrete FET's can be designed like those of conventional silicon-gate devices. No instability due to the tun, neling nitride has been observed in both dc and high-speed switching operations. The technique is useful for MOS VLSI circuits.