Linear Back-projection Method Research Articles

Magneto-thermal-acoustic imaging of magnetic nanoparticles with tissue structure imaging function

Magneto-thermal-acoustic imaging with magnetic nanoparticles (MNPs) is a novel medical imaging modality based on the thermoacoustic (TA) effect of MNPs. We proposed a new dual-modality imaging strategy that combines the TA and echo signals. Based on the synthetic aperture method, we used TA signals to image cancer tissues labeled with MNPs and applied echo signals to achieve tissue structure imaging. In the simulation, we constructed a breast cancer model and assumed that cancer tissue was labeled with MNPs. Under a limited field of view, the TA and echo signals were collected using a multi-element transducer array. By fusing the imaging results of the TA and echo signals, we obtained a boundary distribution map of the breast cancer model, and accurately located the tumor tissue. In this experiment, we built a multi-channel acquisition system. Pork tissue labeled with MNPs was used as the breast cancer phantom. We collected a total of 120 TA and echo signals at 1 mm intervals using a multi-element transducer array and faithfully imaged the boundary distribution map of the phantom. Compared with the traditional linear back projection method based on focused transducers, we demonstrated that the proposed method not only improves the lateral resolution of the image, but also makes accurate cancer identification easier. This provides a promising medical imaging technology for clinical applications.

Anomaly Detection Using Electric Impedance Tomography Based on Real and Imaginary Images.

This research offers a method for separating the components of tissue impedance, namely resistance and capacitive reactance. Two objects that have similar impedance or low contrast can be improved through separating the real and imaginary images. This method requires an Electrical Impedance Tomography (EIT) device. EIT can obtain potential data and the phase angle between the current and the potential measured. In the future, the device is very suitable for imaging organs in the thorax and abdomen that have the same impedance but different resistance and capacitive reactance. This device consists of programmable generators, Voltage Controlled Current Source (VCCS), mulptiplexer-demultiplexer potential meters, and phase meters. Data collecting was done by employing neighboring, while reconstruction was used the linear back-projection method from two different data frequencies, namely 10 kHz and 100 kHz. Phantom used in this experiment consists of distillated water and a carrot as an anomaly. Potential and phase data from the device is reconstructed to produce impedance, real, and imaginary images. Image analysis is performed by comparing the three images to the phantom. The experimental results show that the device is reliable.

Single-Plane Dual-Modality Tomography for Multiphase Flow Imaging by Integrating Electrical Capacitance and Ultrasonic Sensors

This paper presents an experimental study of a single-plane dual-modality tomography (DMT) system integrating electrical capacitance tomography (ECT) and ultrasonic tomography (UT) for water–oil–gas three-phase flow imaging. The soft-field (ECT) and hard-field (UT) systems measure different physical parameters, making them both a fine combination in complementing each system’s limitations. The DMT system consists of 16 units of customized ECT sensors and 16 units of UT transducers, which are composited on a single-plane arrangement to perform concurrent measurement. A finite-element method is used to model and study its feasibility and performance before engaging with the actual hardware. The DMT system is carried out on a vertical test column and horizontal stratified flow to obtain sensor data from each modality by inspection of separate tomographic image using linear back-projection (LBP) image reconstruction algorithm and convolution back projection with Gaussian filtering (CBPF). A fuzzy logic pixel fusion method is used for image fusion process. To evaluate the reconstructed images, the mean structural similarity index (MSSIM) method and the mutual information method ( $M_{F})$ are employed on both the LBP and CBPF image results. The analysis and assessments proved that the CBPF method has successfully improvised the image results and thus has better MSSIM rating and $M_{F}$ over the LBP method with an enhancement up to 12.55% and 8.92%, respectively.

Four Projections CMOS Linear Image Sensor Tomographic Image Reconstruction

This study focused on developing software for image reconstruction system of optical image data obtained from four projections of CMOS linear image sensors by using MATLAB. Four projections of collimated light beams at least must be used in order to avoid aliasing and smear effect that may be appeared on the reconstructed image obtained. The image reconstruction is based on linear back-projection method where transpose matrix, and pseudo-inverse matrix are used to solve inverse matrix problems in MATLAB. Results were compared between both inverse problem calculation methods selected. It was discovered that transpose matrix method performs better than pseudo–inverse matrix for a high resolution images. A graphical user interface has been implemented, it is capable to reconstruct image from raw data collected from sensor. Reconstruction results demonstrated in most cases are able to produce an adequate image for further analysis by user.

EXPERIMENTAL STUDY OF A CAPACITIVE TOMOGRAPHY SYSTEM FOR MULTIPHASE FLOW

This paper presents the experimental development of a capacitive tomography system applied to the study of multiphase flows. A capacitance sensor with eight electrodes and a capacitance measurement transducer were constructed. The two-phase flow void fraction was obtained through an electric-mechanical measurement system. The reconstruction of the image of several two-phase flows was obtained using the linear back projection method. Numerical simulation of the capacitance values between electrode pairs wereperformed, through the method of finite elements, in order to obtain the sensibility maps. This experimental procedure showed the influence of several parameters on the quality of the reconstructed images. The quality of the reconstructed images for air-water and water-oil flows, for different void fractions, demonstrated the validity of the tomography system developed.

Electrodynamics Sensor for the Image Reconstruction Process in an Electrical Charge Tomography System

Electrical charge tomography (EChT) is a non-invasive imaging technique that is aimed to reconstruct the image of materials being conveyed based on data measured by an electrodynamics sensor installed around the pipe. Image reconstruction in electrical charge tomography is vital and has not been widely studied before. Three methods have been introduced before, namely the linear back projection method, the filtered back projection method and the least square method. These methods normally face ill-posed problems and their solutions are unstable and inaccurate. In order to ensure the stability and accuracy, a special solution should be applied to obtain a meaningful image reconstruction result. In this paper, a new image reconstruction method – Least squares with regularization (LSR) will be introduced to reconstruct the image of material in a gravity mode conveyor pipeline for electrical charge tomography. Numerical analysis results based on simulation data indicated that this algorithm efficiently overcomes the numerical instability. The results show that the accuracy of the reconstruction images obtained using the proposed algorithm was enhanced and similar to the image captured by a CCD Camera. As a result, an efficient method for electrical charge tomography image reconstruction has been introduced.

Three-dimensional electrical impedance tomography applied to a metal-walled filtration test platform

The first true three-dimensional image reconstructions from a metal-walled vessel using electrical impedance tomography (EIT) are presented. Two image reconstruction techniques have been applied via relatively sophisticated FEM modelling of a bespoke laboratory test vessel from which data have been obtained using an EIT instrument designed to intrinsically safe requirements. A generalized Tikhonov regularization method is compared with the linear back-projection (LBP) technique. Subsequent image reconstructions strongly suggest that the LBP method when applied to a metal-walled vessel is highly sensitive to the level of detail within the FEM model. By comparison, the regularized technique is far less sensitive to the complexity of the modelled geometry. Additionally, unlike the LBP method, the regularization technique has been successful in accurately reconstructing multiple inhomogeneities within an aqueous system. A further experiment has shown similar sensitivity in a wetted powder-based system. It is concluded that EIT via a regularized difference imaging approach has significant potential for detecting 3D malformations and non-uniformities in industrial pressure filtration systems.

Applications of electrical capacitance tomography in two phase flow visualization

The successful application of Electrical Capacitance Tomography (ECT) depends heavily on the image reconstruction speed and quality. The two requirements usually cannot be satisfied simultaneously. Also, for a large number of acquired 2D ECT images, a 3D presentation of them is much desired to track the variations of the material distribution in a third dimension. To facilitate ECT for practical flow analyses in process engineering, the authors have recently developed algorithms for 3D image presentation and for online iterative image reconstruction that only takes the same time as a linear back projection method but yields good image qualities as the Landweber iterative method does. The new methods have been successfully applied to visualize several classes of two phase flows, namely fluidization, cyclone separation, circulating rate determination in circulating fluidized beds, pneumatic conveying, rotating drum mixing. Special characteristics in each case have been discussed and valuable results are obtained, which are reported in this paper.

An image reconstruction algorithm basedon a revised regularization method for electrical capacitancetomography

The image reconstruction algorithm plays an important rolein electrical capacitance tomography systems. The linearback-projection method is simple and fast, but the reconstructedimage is blurred, A method based on revised regularization isintroduced in this paper. The preliminary experimental resultsshow the method to have advantages as regards the quality ofthe reconstruction image and the reconstruction rate.

キャパシタンスCTとウェーブレット多重解像度を用いた管路内固気二相流の特徴抽出

A concept to extract a feature of solid-air two-phase flow in a pipeline has been launched with a combination of a capacitance-computed tomography and wavelets transform. With this concept, particle distribution images obtained by CT are transformed with discrete wavelets multiresolution. As a result, in the case of low open area ratio of the pipe cross-section, high particle densities are shown in secondarily dominant levels as well as a substantial space level. The high value in the secondary level results from unhomogeneous density due to collision between particles and wall. In the experiment, the CT acquires the capacitances between 12 electrodes distributing around the outside of the pipeline. Clay is attached inside the pipeline in order to verify the open area ratio. The images are reconstructed from the capacitances with a linear back projection method.