Weili Yan

The comparison between FVM and FEM for EIT forward problem

In this paper, the finite volume method (FVM) is introduced in detail for solving the electrical impedance tomography (EIT) forward problem. A new idea for constructing the primary and secondary elements in FVM is presented. Detailed comparisons between FVM and the finite element method (FEM), including the characteristic of the coefficient matrix and the precision of the results, are carried out under the same mesh system. It is shown that accurate estimates of the potential distribution can be obtained with an FVM solution.

The application of the generalized vector sample pattern matching method for EIT image reconstruction

This paper presents a new application of a generalized vector sample pattern matching (GVSPM) method for image reconstruction of conductivity changes in electrical impedance tomography. GVSPM is an iterative method for linear inverse problems. The key concept of the GVSPM is that the objective function is defined in terms of an angular component between the inner product of the known vector and solution of a system of equations. Comparisons are presented between images of simulated and experimental data, reconstructed using truncated singular value decomposition and GVSPM. In both cases, a normalized sensitivity matrix is constructed using the finite volume method to solve the forward problem.

Single trial EEG classification during finger movement task by using hidden Markov models

A new algorithm based on hidden Markov models (HMM) to discriminate single trial electroencephalogram (EEG) between two conditions of finger movement task is proposed. Firstly, multi-channel EEG signals of single trial are filtered in both frequency and spatial domains. The pass bands of the two filters in frequency domain are 0~3 Hz and 8~30 Hz respectively, and the spatial filters are designed by the methods of common spatial subspace decomposition (CSSD). Secondly, two independent features are extracted based on HMM. Finally, the movement tasks are classified into two groups by a perceptron with the extracted features as inputs. With a leave-one out training and testing procedure, an average classification accuracy rate of 93.2% is obtained based on the data from five subjects. The proposed method can be used as an EEG-based brain computer interface (BCI) due to its high recognition rate and insensitivity to noise. In addition, it is suitable for either offline or online EEG analysis

Study of the effects of 50 Hz homogeneous magnetic field on apoptosis and proliferation of SNU cells in vitro

The biological effects of magnetic field on SNU (human low differentiated gastric adenocarcinoma cell line) cells are studied in this paper. SNU cells were randomly divided into control groups and four treatment groups, the treatment groups were respectively irradiated by 50 Hz ferromagnetic field (0.097 T) 5 min., 30 min., 60 min., and 120 min. We observed the effects on proliferation and apoptosis of SNU cells after the treatment of magnetic field by flow cytometric (FCM) DNA analysis and electron microscope observation. The apoptosis rate in treatment groups are 4.75% /spl plusmn/ 1.24%, 6.50% /spl plusmn/ 0.61%, 9.20% /spl plusmn/ 1.76% and 6.26% /spl plusmn/ 2.95% respectively and significantly higher than that in control group. In the irradiation time range from 5 min to 60 min, there is a significant time-depended response correlation of apoptosis rate( r = 0.97, P < 0.01), but FCM results showed that the effects of 50 Hz homogeneous ferromagnetic field on the proliferation and distribution of cell cycle of SNU cells is not significant. We concluded that irradiation of 50 Hz homogeneous ferromagnetic field could promote apoptosis of SNU cells.

Study of the Effects of 50Hz Homogeneous Magnetic Field on Expression of Bax, Bcl-2 and Caspase-3 of SNU Cells In Vitro

We investigate the effects of magnetic field on expression of Bax, Bcl-2 and Caspase-3 of SNU (human low differentiated gastric adenocarcinoma cell line) in this article. SNU cells were randomly divided into control groups and four treatment groups, the treatment groups were respectively irradiated by 50 Hz homogeneous ferromagnetic field (0.097 T) 5 min, 30 min, 60 min and 120 min. SNU cells were harvested for detection of Bax, Bcl-2 and Caspase-3 antigen with flow cytometric analysis (FCM), immunocytochemical staining and Western blot. The expression of Bax and Caspase-3 in all magnetic field exposure groups were higher than that in control by FCM, immunocytochemical stain and Western blot, but the expression of Bcl-2 in all magnetic field exposure groups were lower than that in control by FCM, immunocytochemical stain and Western blot. We concluded that possible mechanisms of apoptosis of SNU cells after 50 Hz homogeneous ferromagnetic field (0.097 T) treatment may be up-regulating the expression of Bax and Caspase-3, down-regulating the expression of Bcl-2

EIT Images with Improved Spatial Resolution Using a Realistic Head Model

A recursive algorithm is presented to improve the spatial resolution of 3-D Electrical Impedance Tomography (EIT) images in a four-shell realistic head model. In this algorithm, the low spatial resolution image derived from the standardized low resolution electromagnetic tomography algorithm (sLORETA) is chosen to be the initial estimate for the Focal Underdetermined System Solver (FOCUSS), and a shrinking strategy is adopted for adjusting the source space during iteration process in FOCUSS. Images are presented with improved spatial resolution and the algorithm effectiveness is verified on simulated data by setting two perturbations in the movement and visual regions of the brain

Spatial resolution improvement of 3D EIT images by the shrinking sLORETA-FOCUSS algorithm

This paper describes the use of the shrinking sLORETA-FOCUSS algorithm to improve the spatial resolution of three-dimensional (3D) EIT images. Conventional EIT yields inaccurate, low spatial resolution images, due to noise, the low sensitivity of boundary voltages to inner conductivity perturbations and a limited number of boundary voltage measurements. The focal underdetermined system solver (FOCUSS) algorithm produces a localized energy solution based on the weighted minimum-norm least-squares (MNLS) solution. It was successfully applied for the spatial resolution improvement of EIT images of simulated and tank data for a 2D homogeneous circular disc. However, due to the fact that a 3D mesh system contains many more elements, much more memory is required to store the weighting matrix. In order to extend the work to 3D, the shrinking-FOCUSS method is utilized to shrink the solution space as well as the weighting matrix in each iteration step. The solution of the standardized low resolution electromagnetic tomography algorithm (sLORETA) is adopted as the initial estimate of the shrinking-FOCUSS. The effectiveness is verified by implementing the new algorithm on tank data for a three-dimensional homogeneous sphere.

Regional head conductivity estimation by the iterative sensitivity matrix method

In this paper, an iterative sensitivity matrix method is proposed to estimate the regional head tissue conductivity. The analytical solution of the electrical impedance tomography (EIT) forward problem is derived for a 2-D concentric circular model. The estimation is verified by a 2-D concentric circular model with 3 layers and a 3-D spherical model with 4 layers, the convergence can be obtained with less iteration number and computational time

The spatial resolution improvement of EIT images by GVSPM-FOCUSS algorithm

The focal underdetermined system solver (FOCUSS) algorithm is a recursive algorithm to find the localized energy solution. It is an initialization-dependent algorithm. The generalized vector sample pattern matching (GVSPM) method has been applied to solve the inverse problem of electrical impedance tomography (EIT) and obtain smooth reconstructed images. By combining the GVSPM solution as the initial estimation of the FOCUSS algorithm, an idea termed the GVSPM-FOCUSS method is presented in this paper to improve the spatial resolution and precision of localization for EIT images. The comparisons are carried out between the EIT images reconstructed with the GVSPM-FOCUSS method and the GVSPM method alone. The effectiveness is verified by simulated and tank data for a model of a two-dimensional homogeneous circular disk.

Effects of 50 Hz ferromagnetic field exposure on apoptosis and proliferation of murine liver cell in vivo

The biological effects of irradiation by magnetic field on the proliferation and apoptosis of the liver cells in mice are studied. BALB/C mice were irradiated by 50 Hz homogeneous ferromagnetic field(0.097 T) and divided into four irradiation groups: 5 min., 30 min., 60 min., and 120 min.. Proliferation and apoptosis of the liver cells were analyzed with the flow cytometry (FCM) and DNA agarose gel electrophoresis. The FCM test results showed that different irradiation time of magnetic field could induce apoptosis of murine liver cells. The percentage of apoptosis in irradiation groups are 9.55%/spl plusmn/0.82%, 12.07%/spl plusmn/2.96%, 13.66%/spl plusmn/1.90% and 16.22%/spl plusmn/2.64% respectively and significantly higher than that in control group. In the interval of 5 min-120 min, the percentage of apoptosis of liver cells increased as the irradiation time prolonged (r=0.78, P<0.05), but FCM results showed that 50 Hz homogeneous ferromagnetic field have no effects on proliferation of murine liver cells. We concluded that irradiation of 50 Hz homogeneous ferromagnetic field could induce and promote apoptosis of murine liver cells in time-effects manner.