Engine flame imaging using electrical capacitance tomography

First results of engine flame imaging using electrical capacitance tomography (ECT) are described. A six-electrode capacitance sensor fabricated as part of a research engine provides 15 capacitance measurements per scan. A transputer-based ECT system is used to reconstruct the cross-sectional images of flames in the engine from successive sets of capacitance measurements. The prototype system is capable of capturing flame images at 315 frames per second and has potential for monitoring engine performance     

基于无线层析成像和卡尔曼滤波的定位追踪

无线传感网的无源定位问题对现实社会有着重要意义,通过对局域范围内的RSSI进行捕捉,并根据RSSI的变化在区域内的衰减,再依据线型模型进行计算,从而得到局域范围内的位置坐标。将每次采样得到的位置坐标信息进行预处理,再通过卡尔曼滤波进行优化,从而形成物体运动的轨迹。     

Dynamic imaging and tracer kinetic modeling for emission tomography using rotating detectors

When performing dynamic studies using emission tomography the tracer distribution changes during acquisition of a single set of projections. This is particularly true for some positron emission tomography (PET) systems which, like single photon emission computed tomography (SPECT), acquire data over a limited angle at any time, with full projections obtained by rotation of the detectors. In this paper, an approach is proposed for processing data from these systems, applicable to either PET or SPECT. A method of interpolation, based on overlapped parabolas, is used to obtain an estimate of the total counts in each pixel of the projections for each required frame-interval, which is the total time to acquire a single complete set of projections necessary for reconstruction. The resultant projections are reconstructed using traditional filtered backprojection (FBP) and tracer kinetic parameters are estimated using a method which relies on counts integrated over the frame-interval rather than instantaneous values. Simulated data were used to illustrate the technique's capabilities with noise levels typical of those encountered in either PET or SPECT. Dynamic datasets were constructed, based on kinetic parameters for fluoro-deoxy-glucose (FDG) and use of either a full ring detector or rotating detector acquisition. For the rotating detector, use of the interpolation scheme provided reconstructed dynamic images with reduced artefacts compared to unprocessed data or use of linear interpolation. Estimates for the metabolic rate of glucose had similar bias to those obtained from a full ring detector.     

Discrete tomography in medical imaging

Discrete tomography (DT) deals with the reconstruction of a function from its projections, when the function has a known discrete range. The knowledge of the discrete range, possibly together with some prior information, can significantly reduce the number of projections required for a high-quality reconstruction. The reconstruction methods used in DT applications are usually based on some formulation as an optimization problem. This paper presents methods and results of DT based on problems of angiography, emission tomography, and electron microscopy (EM).     

Hybrid small animal imaging system combining magnetic resonance imaging with fluorescence tomography using single photon avalanche diode detectors

The high sensitivity of fluorescence imaging enables the detection of molecular processes in living organisms. However, diffuse light propagation in tissue prevents accurate recovery of tomographic information on fluorophore distribution for structures embedded deeper than 0.5 mm. Combining optical with magnetic resonance imaging (MRI) provides an accurate anatomical reference for fluorescence imaging data and thereby enables the correlation of molecular with high quality structural/functional information. We describe an integrated system for small animal imaging incorporating a noncontact fluorescence molecular tomography (FMT) system into an MRI detector. By adopting a free laser beam design geometrical constraints imposed by the use of optical fibers could be avoided allowing for flexible fluorescence excitation schemes. Photon detection based on a single-photon avalanche diode array enabled simultaneous FMT/MRI measurements without interference between modalities. In vitro characterization revealed good spatial accuracy of FMT data and accurate quantification of dye concentrations. Feasibility of FMT/MRI was demonstrated in vivo by simultaneous assessment of protease activity and tumor morphology in murine colon cancer xenografts.     

Enhancing impedance imaging through multimodal tomography

Several noninvasive modalities including electrical impedance tomography (EIT), magnetic induction tomography (MIT), and induced-current EIT (ICEIT) have been developed for imaging the electrical conductivity distribution within a human body. Although these modalities differ in how the excitation and detection circuitry (electrodes or coils) are implemented, they share a number of common principles not only within the image reconstruction approaches but also with respect to the basic principle of generating a current density distribution inside a body and recording the resultant electric fields. In this paper, we are interested in comparing differences between these modalities and in theoretically understanding the compromises involved, despite the increased hardware cost and complexity that such a multimodal system brings along. To systematically assess the merits of combining data, we performed 3-D simulations for each modality and for the multimodal system by combining all available data. The normalized sensitivity matrices were computed for each modality based on the finite element method, and singular value decomposition was performed on the resultant matrices. We used both global and regional quality measures to evaluate and compare different modalities. This study has shown that the condition number of the sensitivity matrix obtained from the multimodal tomography with 16-electrode and 16-coil is much lower than the condition number produced in the conventional 16-channel EIT and MIT systems, and thus, produced promising results in terms of image stability. An improvement of about 20% in image resolution can be achieved considering feasible signal-to-noise ratio levels.     

X-ray computed tomography for medical imaging

The article looks at reconstruction in 2-D and 3-D tomography. We have not dealt with some of the issues in reconstruction such as sampling and aliasing artifacts, finite detector aperture artifacts, beam hardening artifacts, etc., in greater detail since these are beyond the scope of an introductory tutorial. We examine the physical and mathematical concepts of the Radon (1917) transform, and the basic parallel beam reconstruction algorithms are discussed. We also develop the algorithms for fan-beam CT, and discuss the mathematical principles of cone-beam CT     

Coherent Doppler tomography for microwave imaging

A tomographic extension of the type of microwave Doppler imaging typified by synthetic aperture radar has recently been developed and shown experimentally to exhibit a high degree of spatial resolution. When CW irradiation is used, the sidelobes in the pointspread function are inherently high and tend to limit the dynamic range of the reconstructed images. The point-spread function of a system using CW irradiation and an aperture that completely surrounds the object has a central lobe of width of λ/5, but the first sidelobe is only 8 dB below the central peak. The limitation due to the high sidelobes can be partially overcome by using wide-band signals or bistatic diversity. One of the steps in reconstructing a coherent Doppler tomogram is to perform a two-dimensional Fourier transform. The ordinary two-dimensional discrete Fourier transform (DFT) produces points in the transform space on a Cartesian raster. In coherent Doppler tomography (CDT), however, the data are sampled on a polar raster. To diminish the computational burden associated with converting to the Cartesian raster and interpolating, we have developed an alternative algorithm which requires no interpolation and is based on interpreting the two-dimensional Fourier transform as a one-dimensional circular convolution integral. The quality of the images computed in this fashion compares favorably with that for the old method and the computational burden is greatly reduced.     

Theoretical analysis and optimization of electromagnetic actuation in a valveless microimpedance pump

The construction of a novel valveless microimpedance pump is proposed and the utilized electromagnetic actuator is designed and optimized in this study. The actuating mechanism comprises an electroplated permanent magnet mounted on a flexible PDMS diaphragm and electroplated Cu coils located on a glass substrate. The electromagnetic force between the magnet and the Cu coils causes the diaphragm to deflect and then creates the accumulative effects of wave propagation and reflection at the junction of the compressible and rigid sections. The resulting pressure gradient in the fluid drives the flow from the inlet to the outlet of the micropump. The constituent parts of the electromagnetic actuator, namely the diaphragm, the microcoils, and the magnet are modeled and analyzed in order to optimize the actuator design. The design models are verified both theoretically and numerically and the relationships between the magnetic force, diaphragm displacement, and diaphragm strength are established. The magnitude of the magnetic force acting on the flexible diaphragm are calculated using Ansoft/Maxwell3D FEA software and the resulting diaphragm deflection simulated by ANSYS FEA software are found to agree with the theoretical predictions. Different diaphragm shapes are investigated and their relative strength and flexibility are compared. It is found that a circular PDMS diaphragm represents the most appropriate choice for the actuating mechanism in the micropump. The desired diaphragm deflection of 15 μm is obtained using a compression force of 16 μN, generated by a coil input current of 0.9 A. The diaphragm deflection can be regulated by varying the current passed through the microcoil and hence the flow rate can be controlled. The valveless microimpedance pump proposed in this study is easily fabricated and can be readily integrated with existing biomedical chips due to its plane structure. The results of the present study provide a valuable contribution to the ongoing development of Lab-on-a Chip systems.     

光学相干层析系统的成像数学模型研究

生物组织样品的光学特性可以由光学相干层析成像系统探测到的后向散射功率确定，文中建立了入射光线在样品介质内的一阶散射数学模型，揭示了样品的衰减系数和后向散射系数与系统探测结果之间的关系。     

Improving microwave imaging by enhancing diffraction tomography

In this paper, a technique for enhancing the reconstruction quality of diffraction tomography for microwave imaging is presented. The technique invokes the WKB approximation in conjunction with utilizing measurement data at more than one frequency to overcome some of the limitations of diffraction tomography. The resulting formulation has a mathematical interpretation which leads to some interesting insights into the limitations of diffraction tomography. Numerical implementation of the technique is also described and actual simulation results using this implementation for a variety of two-dimensional (2-D) objects are provided. These show that indeed significant improvements over conventional diffraction tomography are possible with our enhanced technique     

太赫兹计算机辅助层析成像发展近况

由于太赫兹波可穿透塑料、纸张、衣服等非金属、非极性物质,较X辐射具有较低的光子能量,且计算机辅助层析成像(CT)可获得物体内部结构信息,并可重构出物体的三维图像,因此太赫兹CT受到国际广泛关注。重点介绍了近年来太赫兹CT研究重点及具体状况,并分析了存在的问题和发展趋势。可为我国太赫兹CT技术的发展提供技术借鉴。     

雷达成像和衍射层析的内在联系梳理

从方程描述、方程求解和方程解析解三个层面,对雷达成像和衍射层析的内在联系进行了系统性梳理.首先,介绍了描述成像问题的电磁散射方程,发现描述雷达的方程是二维的面积分方程,而描述衍射层析的方程是三维的体积分方程.指出成像对象不同是导致方程不同的根源,并利用等效原理建立了两种成像间的联系.其次,指出两种成像的相同点是,对非线性的电磁散射方程的线性化近似求解.最后,指出两种成像的回波信号(在空间谱域)和成像目标(在空间域)均构成一组傅里叶变换对.给出了两种成像的解析解的统一数学模型,即成像结果可表示为观测点(散射系数或散射势)卷积点扩展函数(PSF)的形式.通过PSF对两者的成像性能进行了比较.     

Electrical impedance tomography for imaging tissue electroporation

Electroporation is a method to introduce molecules, such as gene constructs or small drugs, into cells by temporarily permeating the cell membrane with electric pulses. In molecular medicine and biotechnology, tissue electroporation is performed with electrodes placed in the target area of the body. Currently, tissue electroporation, as with all other methods of molecular medicine, is performed without real-time control or near-term information regarding the extent and degree of electroporation. This paper expands the work from our previous study by implementing new ex vivo experimental data with "front-tracking" analysis for the image reconstruction algorithm. The experimental data is incorporated into numerical simulations of electroporation procedures and images are generated using the new reconstruction algorithm to demonstrate that electrical impedance tomography (EIT) can produce an image of the electroporated area. Combining EIT with electroporation could become an important biotechnological and medical technique to introduce therapeutic molecules into cells in tissue at predetermined areas of the body.     

Three-gamma annihilation imaging in positron emission tomography

It is argued that positron annihilation into three photons, although quite rare, could still be used as a new imaging modality of positron emission tomography. The information gained when the three decay photons are detected is significantly higher than in the case of 511 keV two-gamma annihilation. The performance of three-gamma imaging in terms of the required detector properties, spatial resolution and counting rates is discussed. A simple proof-of-principle experiment confirms the feasibility of the new imaging method.     

基于相干层析的太赫兹成像技术研究

介绍了一种结合光学相干层析技术和太赫兹技术的太赫兹三维成像技术——太赫兹相干层析成像技术。该技术利用宽频太赫兹的弱相干原理,可以实现对待测样品进行高精度的三维成像。实验结果表明太赫兹相干层析成像技术的纵向分辨能力高于100 μm。在纵向探测精度方面,该技术相对传统的方案有了较大的提高,在高精度太赫兹无损探测领域具有巨大的应用前景。     

Fluorescent protein tomography scanner for small animal imaging

Microscopy of fluorescent proteins has enabled unprecedented insights into visualizing gene expression in living systems. Imaging deeper into animals, however, has been limited due to the lack of accurate imaging methods for the visible. We present a novel system designed to perform tomographic imaging of fluorescent proteins through whole animals. The tomographic method employed a multiangle, multiprojection illumination scheme, while detection was achieved using a highly sensitive charge-coupled device camera with appropriate filters. Light propagation was modeled using a modified solution to the diffusion equation to account for the high absorption and high scattering of tissue at the visible wavelengths. We show that the technique can quantitatively detect fluorescence with sub millimeter spatial resolution both in phantoms and in tissues. We conclude that the method could be applied in tomographic imaging of fluorescent proteins for in vivo targeting of different diseases and abnormalities.     

Microwave tomography: two-dimensional system for biological imaging

Microwave tomographic imaging is one of the new technologies which has the potential for important applications in medicine. Microwave tomographically reconstructed images may potentially provide information about the physiological state of tissue as well as the anatomical structure of an organ. A two-dimensional (2-D) prototype of a quasi real-time microwave tomographic system was constructed. It was utilized to reconstruct images of physiologically active biological tissues such as an explanted canine perfused heart. The tomographic system consisted of 64 special antennae, divided into 32 emitters and 32 receivers which were electronically scanned. The cylindrical microwave chamber had an internal diameter of 360 mm and was filled with various solutions, including deionized water. The system operated on a frequency of 2.45 GHz. The polarization of the incident electromagnetic field was linear in the vertical direction. Total acquisition time was less than 500 ms. Both accurate and approximation methods of image reconstruction were used. Images of 2-D phantoms, canine hearts, and beating canine hearts have been achieved. In the worst-case situation when the 2-D diffraction model was used for an attempt to “slice” three-dimensional (3-D) object reconstruction, the authors still achieved spatial resolution of 1 to 2 cm and contrast resolution of 5%     

多数据源电离层层析成像方法

卫星信标电离层层析成像（CIT）是一种高度不适定性问题,有限视角、稀疏布站等原因造成电离层CIT数据采集严重不完整,CIT结果精度不高,尤其是垂直误差可达50 km以上。为了解决CIT结果精度不高的问题,提出一种融合地面垂测、斜测数据、顶部探测仪数据和三频卫星信标数据的多数据源电离层联合CIT方法。该方法采用建立在实测数据基础上的迭代初值,与实际偏离较小,能够提高CIT反演结果的精度;同时地基设备和顶部探测设备有较高的垂直分辨率,与卫星信标结合能够有效解决有限视角问题,提高CIT结果的垂直分辨率。     

Ionospheric tomography using GNSS reflections

We report a preliminary analysis of the impact of Global Navigation Satellite System Reflections (GNSS-R) data on ionospheric monitoring over the oceans. The focus is on a single polar Low Earth Orbiter (LEO) mission exploiting GNSS-R as well as Navigation (GNSS-N) and Occultation (GNSS-O) total electron content (TEC) measurements. In order to assess impact of the data, we have simulated GNSS-R/O/N TEC data as would be measured from the LEO and from International Geodesic Service (IGS) ground stations, with an electron density (ED) field generated using a climatic ionospheric model. We have also developed a new tomographic approach inspired by the physics of the hydrogen atom and used it to effectively retrieve the ED field from the simulated TEC data near the orbital plane. The tomographic inversion results demonstrate the significant impact of GNSS-R: three-dimensional ionospheric ED fields are retrieved over the oceans quite accurately, even as, in the spirit of this initial study, the simulation and inversion approaches avoided intensive computation and sophisticated algorithmic elements (such as spatio-temporal smoothing). We conclude that GNSS-R data over the oceans can contribute significantly to a Global/GNSS Ionospheric Observation System (GIOS).