Weizhong Dai

Tri-polar concentric ring electrode development for Laplacian electroencephalography

Brain activity generates electrical potentials that are spatio-temporal in nature. Electroencephalography (EEG) is the least costly and most widely used noninvasive technique for diagnosing many brain problems. It has high temporal resolution, but lacks high spatial resolution. In an attempt to increase the spatial selectivity, researchers introduced a bipolar electrode configuration utilizing a five-point finite difference method (FPM) and others applied a quasi-bipolar (tri-polar with two elements shorted) concentric electrode configuration. To further increase the spatial resolution, the authors report on a tri-polar concentric electrode configuration for approximating the analytical Laplacian based on a nine-point finite difference method (NPM). For direct comparison, the FPM, quasi-bipolar method (a hybrid NPM), and NPM were calculated over a 400 times 400 mesh with 1/400 spacing using a computer model. A closed-form analytical computer model was also developed to evaluate and compare the properties of concentric bipolar, quasi-bipolar, and tri-polar electrode configurations, and the results were verified with tank experiments. The tri-polar configuration and the NPM were found to have significantly improved accuracy in Laplacian estimation and localization. Movement-related potential (MRP) signals were recorded from the left prefrontal lobes on the scalp of human subjects while they performed fast repetitive movements. Disc, bipolar, quasi-bipolar, and tri-polar electrodes were used. MRP signals were plotted for all four electrode configurations. The signal-to-noise ratio and spatial selectivity of the MRP signals acquired with the tri-polar electrode configuration were significantly better than the other configurations

A compact finite-difference scheme for solving a one-dimensional heat transport equation at the microscale: 431

Heat transport at the microscale is of vital importance in microtechnology applications. The heat transport equation is different from the traditional heat diffusion equation since a second-order derivative of temperature with respect to time and a third-order mixed derivative of temperature with respect to space and time are introduced. In this study, we develop a high-order compact finite-difference scheme for the heat transport equation at the microscale. It is shown by the discrete Fourier analysis method that the scheme is unconditionally stable. Numerical results show that the solution is accurate.

Development of a Tri-polar Concentric Ring Electrode for Acquiring Accurate Laplacian Body Surface Potentials

Potentials recorded on the body surface from the heart are of a spatial and temporal function. The 12-lead electrocardiogram (ECG) provides a useful means of global temporal assessment; however, it yields limited spatial information due to the smoothing effect caused by the volume conductor. In an attempt to circumvent the smoothing problem, researchers have used the five-point method (FPM) to numerically estimate the analytical solution of the Laplacian with an array of monopolar electrodes. Researchers have also developed a bipolar concentric ring electrode system to estimate the analytical Laplacian, and others have used a quasi-bipolar electrode configuration. In a search to find an electrode configuration with a close approximation to the analytical Laplacian, development of a tri-polar concentric ring electrode based on the nine-point method (NPM) was conducted. A comparison of the NPM, FPM, and discrete form of the quasi-bipolar configuration was performed over a 400 × 400 mesh with 1/400 spacing by computer modeling. Different properties of bipolar, quasi-bipolar and tri-polar concentric ring electrodes were evaluated and compared, and verified with tank experiments. One-way analysis of variance (ANOVA) with post hoc t-test and Bonferroni corrections were performed to compare the performance of the various methods and electrode configurations. It was found that the tri-polar electrode has significantly improved accuracy and local sensitivity. This paper also discusses the development of an active sensor using the tri-polar electrode configuration. A 1-cm active Laplacian tri-polar sensor based on the NPM was tested and deemed feasible for acquiring Laplacian cardiac surface potentials.

An unconditionally stable finite difference scheme for solving a 3D heat transport equation in a sub-microscale thin film

Heat transport at the microscale is of vital importance in microtechnology applications. The heat transport equation is different from the traditional heat diffusion equation since a second-order derivative of temperature with respect to time and a third-order mixed derivative of temperature with respect to space and time are introduced. In this study, we develop a finite difference scheme with two levels in time for the 3D heat transport equation in a sub-microscale thin film. It is shown by the discrete energy method that the scheme is unconditionally stable. The 3D implicit scheme is then solved by using a preconditioned Richardson iteration, so that only a tridiagonal linear system is solved for each iteration. The numerical procedure is employed to obtain the temperature rise in a gold sub-microscale thin film.

Optimal temperature distribution in a three dimensional triple-layered skin structure with embedded vasculature

In recent years there has been interest in research related to hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. When heating the tumor tissue, the crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Hence, in order to control the process, it is important to obtain a temperature field of the entire treatment region. Recently, we have developed a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure. In this article, we extend our study to a triple-layered skin structure embedded with multilevel blood vessels, and develop a numerical method for obtaining an optimal temperature distribution.

A finite difference method for studying thermal deformation in a thin film exposed to ultrashort-pulsed lasers

Ultrashort-pulsed lasers have been attracting worldwide interest in science and engineering. Studying the thermal deformation induced by ultrashort-pulsed lasers is important for preventing thermal damage. This article presents a finite difference method for studying thermal deformation in a thin film exposed to ultrashort-pulsed lasers. The method is obtained based on the parabolic two-step model. It accounts for the coupling effect between lattice temperature and strain rate, as well as for the hot-electron-blast effect in momentum transfer. The method allows us to avoid non-physical oscillations in the solution as demonstrated by numerical examples.

A Numerical Method for Optimizing Laser Power in the Irradiation of a 3-D Triple-Layered Cylindrical Skin Structure

ABSTRACT It is of interest to research hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. The crucial problem is to keep surrounding normal tissue below a temperature that will produce harm when heating the tumor tissue. In this study, we develop a numerical model for optimizing laser power in the irradiation of a 3-D triple-layered cylindrical skin structure. The method determines the required laser intensity in order to obtain prespecified temperatures at given locations on the skin surface after a prespecified laser exposure time.

An approximate analytic method for solving 1D dual-phase-lagging heat transport equations

Abstract In this study, we develop an approximate analytic method for solving 1D dual-phase-lagging heat conduction equations, which are derived based on the original dual-phase-lagging model without the first-order Taylor series approximation. The approximate analytic solution is obtained by employing the method of separation of variables. The coefficients of the series solution are then approximated by polynomials. The numerical method is illustrated with two simple examples.

Optimal Temperature Distribution in a Three-Dimensional Triple-Layered Skin Structure Embedded with Artery and Vein Vasculature

In recent years there has been interest in research related to hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. When heating the tumor tissue, the crucial problem is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Hence, in order to control the process, it is important to obtain a temperature field of the entire treatment region. In this article, we develop a numerical method for obtaining an optimal temperature distribution in a triple-layered skin structure embedded with two countercurrent, multilevel blood vessels: artery and vein.

A Numerical Method for Obtaining an Optimal Temperature Distribution in a 3-D Triple-Layered Cylindrical Skin Structure Embedded with a Blood Vessel

ABSTRACT In hyperthermia cancer treatments, the crucial problem, when heating the tumor tissue, is keeping the temperature of the normal tissue surrounding the tumor below a certain threshold so as not to cause damage to the tissue. Thus, it is important to optimize the temperature field of the entire treatment region. Recently, we have developed a numerical method for obtaining an optimal temperature distribution in a triple-layered cylindrical skin structure. In this article, we extend our method to a case involving a triple-layered cylindrical skin structure embedded with a blood vessel. The method is illustrated by a numerical example.