Haijun Luo

A multi-channel magnetic induction tomography measurement system for human brain model imaging

This paper proposes a multi-channel magnetic induction tomography measurement system for biological conductivity imaging in a human brain model. A hemispherical glass bowl filled with a salt solution is used as the human brain model; meanwhile, agar blocks of different conductivity are placed in the solution to simulate the intracerebral hemorrhage. The excitation and detection coils are fixed co-axially, and the axial gradiometer is used as the detection coil in order to cancel the primary field. On the outer surface of the glass bowl, 15 sensor units are arrayed in two circles as measurement parts, and a single sensor unit for cancelling the phase drift is placed beside the glass bowl. The phase sensitivity of our system is 0.204 degrees /S m(-1) with the excitation frequency of 120 kHz and the phase noise is in the range of -0.03 degrees to +0.05 degrees . Only the coaxial detection coil is available for each excitation coil; therefore, 15 phase data are collected in each measurement turn. Finally, the two-dimensional images of conductivity distribution are obtained using an interpolation algorithm. The frequency-varying experiment indicates that the imaging quality becomes better as the excitation frequency is increased.

Magnetic induction tomography: simulation study on the forward problem

Magnetic induction tomography (MIT) is a kind of electromagnetic detecting and imaging technology, which is considered to be useful for diagnoses of the intracranial hemorrhage. The forward problem is the eddy current problem which is useful for improving the resolution of the measurement system and provides basic data for the inverse problem of image reconstruction. Simulation study on the forward problem in this paper includes four parts: illustration of the concept of a new MIT system, establishment of a mathematical model for the forward problem, creation of the human brain model and image visualization of the intracranial hemorrhage. In the results, the mathematical model was established with the edge finite element method, and MIT image visualization was realized under the real human brain 3D model. This study provides a foundation for MIT in the future clinical application.

A COMBINED REGULARIZATION ALGORITHM FOR ELECTRICAL IMPEDANCE TOMOGRAPHY SYSTEM USING RECTANGULAR ELECTRODES ARRAY

A novel Electrical Impedance Tomography system with rectangular electrodes array and back electrode is proposed. This system could reconstruct a deeper target and is easy to operate. By studying different reconstructed algorithms: Tikhonov regularization and the Newtons One-step Error Reconstructor (NOSER), a combined regularization algorithm is proposed. The L-curve and posteriori method are used to choose Tikhonov and NOSER regularization parameter. Two evaluation parameters of reconstructed algorithm: normalization mean square distance criterion (NMSD), normalized mean absolute distance criterion (NMAD) are used to evaluate the results precision of inverse problem quantificationally. The comparison among Tikhonov regularization, NOSER and the combined regularization shows that the ill-condition and the error of inverse problem are reduced. This new algorithm can decrease condition number by 70%, NMSD by 51%, and NMAD by 41% at least. Simulate results show that the combined regularization algorithm could reconstructed the target image in the depth from 10–40 mm. The experimental results show that a 15 mm × 9 mm × 9 mm cuboids whose depth is 35 mm could be distinguished. The performance of this system and the combined regularization algorithm demonstrate significantly better spatial resolution and minor reconstructed error.

Open Electrical Impedance Tomography: Computer Simulation and System Realization

Electrical impedance tomography (EIT) is a non-invasive technique used to image the electrical conductivity and permittivity within a body from measurements taken on body’s surface. But the low spatial resolution of imaging, complicated operation and the asymmetrical placement of electrodes make the EIT cannot achieve the requirements of clinical application. In this paper, we proposed a novel idea of open electrical impedance tomography (OEIT) and a new type of electrode to provide more valuable distribution information of electrical impedance for local subsurface biological tissues than closed EIT. The OEIT system is constructed. The electromagnetic mathematical models of OEIT are presented and a method to solving the boundary value problem of half infinite calculating region is proposed for the computer simulations. Furthermore, we have realized the OEIT system, and completed the physics and the clinical experiments. Experiment results show that the OEIT system can obtain a better resolution and positioning accuracy, and is more suitable for clinical application.

V-shaped portable NMR sensor with a deep penetration depth and its application in assessing the aging level of turbine oils in power stations

This paper presents a simple design for a nuclear magnetic resonance (NMR) sensor and its application for detecting turbine oil in two power stations. The magnet, which is composed of two identical cuboid permanent magnet blocks and two iron shimming sheets of a special shape, generates a relatively homogeneous static magnetic B0 field (∼ 364 ppm) on a 10 × 10 mm 2 region of interest. In the vertical direction, it produces a constant gradient of ∼15.5 T/m within 5 mm which allows for self-diffusion measurements and 1 dimensional imaging. This NMR sensor can produce a deep penetration depth into the samples with relatively strong and uniform B0 strength. The NMR sensor was specially designed for assessing the aging status of turbine oil in a power station, and a group of turbine oil of different service times was measured. Results demonstrate that an increase in the service time of the turbine oils clearly decreases transverse relaxation time T2. This portable sensor can be used in fields and provide quantitative evaluation parameters of the aging status of turbine oil during periodic inspection.

An image reconstruction method for magnetic induction tomography: improved genetic algorithm

Magnetic induction tomography (MIT) is a new medical functional imaging technique. This paper proposes a multi-layer model of the biological tissue. And a new reconstruction method of magnetic induction tomography based on the improved genetic algorithm(GA) was introduced. The GA was improved from the following aspects: the generation of the initial population, selection, crossover and mutation operation. The simulation results indicate that the method can reflect local and large-area bleeding in the shallow of biological tissue, and construct a base for the future clinical brain disease monitoring.

Multi-channel magnetic induction tomography measurement system

Magnetic induction tomography(MIT) is a noninvasive and contactless medical imaging technique. The 16 channels of MIT system is showed in the paper, which image for the low conductivity object with working at 1MHz. In the study, we use the water tanker filled with salt solution and the different conductivity agar blocks to simulate the human brain with edema or hematoma. The each sensor is composed of the excitation coil, the two detection coils, a preamplifier board and a power amplifier board, which were fixed by four plastic columns. This paper researches the sensitivity and stability of single sensor unit, and the phase sensitivity of the system is 0.29°/S·m−1 and the phase drift is in the range of −0.02° to +0.06° over 30 minutes. Finally, the 2-dimensional images of conductivity distribution are obtained using the inverse distance weighted spatial interpolation algorithm of and the direct projection way.

Analytical solution to the three-dimensional head eit forward problem: Calculation and simulation with a 4-layer spherical volume conductor

A 4-layer concentric spherical model of human head was built to simulate the head EIT forward problem. The layers from outside to inside are scalp, skull, CFS (Cerebrospinal fluid) and brain tissue, respectively. A pair of point curren t sources placed on the outmost layer is regarded as the boundary condition, and an analytical method of separation of variables was employed to solve the problem. The electric potentials of different current injecting angles were calculated and the eq uipotential lines were drawn. The simulation results revealed that, the increment of the brain tissue conductivity causes decrease of the magnitude of both real and imaginary parts of the electric potential on the scalp. The frequency property of the model was simulated, when the exciting frequency was increased, the imaginary part of the electric potential increased significa ntly. These analytical solutions could be used to analyze the head EIT problems and check the numerical solutions calculated from FEM or BEM.