Time-coded aperture tomography: experimental results

In this paper, we discuss the applicability of a time-coded aperture system especially designed for thyroid tomography on the basis of phantom experiments. Our studies show that 1) the quality of the reconstructions is high (e.g., a cold spot of 6 mm diameter in a thyroid phantom can easily be detected), and 2) the reconstruction can be carried out in less than 11 min on a standard 16 bit minicomputer (HP1000). It is therefore concluded that the clinical potentiality of the device is good.     

Space–Time-Coded MIMO ZP-OFDM Systems: Semiblind Channel Estimation and Equalization

The space–time-block-code (STBC) multiple-input–multiple-output (MIMO) zero-padding orthogonal frequency-division multiplexing (ZP-OFDM) has been widely investigated in recent years. It provides a good performance for the multiuser scenario with a small number of pilots. However, it would fail in the face of complex symmetric signals. In this paper, novel channel estimation and equalization for complex input signals are investigated. With the Alamouti-like STBC scheme, the channel impulse responses of the space–time-coded MIMO ZP-OFDM system are shown to be identifiable up to two ambiguity matrices by subspace channel estimation. The frequency domain minimum mean-square error (MMSE) equalizer is then employed to detect the OFDM symbols. Furthermore, we propose a forward–backward averaging technique to enhance the performances of blind channel estimation. The weight analysis for the MMSE equalizer is also conducted to reduce the complexity of system design. Computer simulations demonstrate the effectiveness and correctness of channel estimation and weight analysis for the space–time-coded MIMO ZP-OFDM systems.      

Review of Terahertz Tomography Techniques

Terahertz and millimeter waves penetrate various dielectric materials, including plastics, ceramics, crystals, and concrete, allowing terahertz transmission and reflection images to be considered as a new imaging tool complementary to X-Ray or Infrared. Terahertz imaging is a well-established technique in various laboratory and industrial applications. However, these images are often two-dimensional. Three-dimensional, transmission-mode imaging is limited to thin samples, due to the absorption of the sample accumulated in the propagation direction. A tomographic imaging procedure can be used to acquire and to render three-dimensional images in the terahertz frequency range, as in the optical, infrared or X-ray regions of the electromagnetic spectrum. In this paper, after a brief introduction to two dimensional millimeter waves and terahertz imaging we establish the principles of tomography for Terahertz Computed tomography (CT), tomosynthesis (TS), synthetic aperture radar (SAR) and time-of-flight (TOF) terahertz tomography. For each technique, we present advantages, drawbacks and limitations for imaging the internal structure of an object.     

Feasibility of half-data image reconstruction in 3-D reflectivity tomography with a spherical aperture

Reflectivity tomography is an imaging technique that seeks to reconstruct certain acoustic properties of a weakly scattering object. Besides being applicable to pure ultrasound imaging techniques, the reconstruction theory of reflectivity tomography is also pertinent to hybrid imaging techniques such as thermoacoustic tomography. In this work, assuming spherical scanning apertures, redundancies in the three-dimensional (3-D) reflectivity tomography data function are identified and formulated mathematically. These data redundancies are used to demonstrate that knowledge of the measured data function over half of its domain uniquely specifies the 3-D object function. This indicates that, in principle, exact image reconstruction can be performed using a "half-scan" data function, which corresponds to temporally untruncated measurements acquired on a hemi-spherical aperture, or using a "half-time" data function, which corresponds to temporally truncated measurements acquired on the entire spherical aperture. Both of these minimal scanning configurations have important biological imaging applications. An iterative reconstruction method is utilized for reconstruction of a simulated 3-D object from noiseless and noisy half-scan and half-time data functions.     

眼检光学相干层析成像系统及实验研究

眼检光学相干层析 (opticalcoherencetomography)成像技术是一种新型成像方法 ,本文阐述了OCT系统的基本原理、组成、建立了一种相干成像实验装置 ,用该实验装置得到了纵向分辨率为 10 μm的实验结果 ,最后 ,本文给出了OCT眼检系统的实验结果     

板壳状微电子器件的数字层析成像检测方法

 传统工业CT(industrial computed tomography, ICT)成像方法受扫描原理和探测器、射线源等硬件条件的限制,难以对芯片、印刷电路板等板、壳状微电子器件实施有效的数字层析成像检测. 为此,讨论了一种基于锥束射线倾斜扫描和代数重建技术（Algebraic Reconstruction Technique, ART）的薄板层析成像（Computed Laminography, CL）方法,研究了其基于投影凸集理论的投影预处理方法及基于不同区域相似性的重建图像非局部平均降噪后处理方法,建立了基于非晶硅面阵探测器的实验系统,并完成了CPU芯片和印刷电路板的CL成像. 实验结果证明了该方法的正确性.     

Multifunctional Carbon–Silica Nanocapsules with Gold Core for Synergistic Photothermal and Chemo‐Cancer Therapy under the Guidance of Bimodal Imaging

Carbon‐based nanomaterials have been developed for photothermal cancer therapy, but it is still a great challenge to fabricate their multifunctional counterparts with facile methods, good biocompatibility and dispersity, and high efficiency for cancer theranostics. In this work, an alternative multifunctional nanoplatform is developed based on carbon–silica nanocapsules with gold nanoparticle in the cavity (Au@CSN) for cancer theranostics. The encapsulated chemodrug doxorubicin can be released from the Au@CSN with mesoporous and hollow structure in a near‐infrared light and pH stimuli‐responsive manner, facilitating spatiotemporal therapy to decrease off‐target toxicity. The nanocapsules with efficient photothermal conversion and excellent biocompatibility achieve a synergistic effect of photothermal and chemotherapy. Furthermore, the nanocapsules can act as a multimodal imaging agent of computed tomography and photoacoustic tomography imaging for guiding the therapy. This new design platform can provide a promising strategy for precise cancer theranostics.     

Interactive display and analysis of 3-D medical images

The ANALYZE software system, which permits detailed investigation and evaluation of 3-D biomedical images, is discussed. ANALYZE can be used with 3-D imaging modalities based on X-ray computed tomography, radionuclide emission tomography, ultrasound tomography, and magnetic resonance imaging. The package is unique in its synergistic integration of fully interactive modules for direct display, manipulation, and measurement of multidimensional image data. One of the most versatile and powerful capabilities in ANALYZE is image volume rendering for 3-D display. An important advantage of this technique is that it can be used to display 3-D images directly from the original data set and to provide on-the-fly combinations of selected image transformations, such as surface segmentation, cutting planes, transparency, and/or volume set operations (union, intersection, difference, etc.). The module has been optimized to be fast (interactive) without compromising image quality. The software is written entirely in C and runs on standard UNIX workstations.     

Half-time image reconstruction in thermoacoustic tomography

Thermoacoustic tomography (TAT) is an emerging imaging technique with great potential for a wide range of biomedical imaging applications. In this paper, we propose and investigate reconstruction approaches for TAT that are based on the half-time reflectivity tomography paradigm. We reveal that half-time reconstruction approaches permit for the explicit control of statistically complementary information that can result in the optimal reduction of image variances. We also show that half-time reconstruction approaches can mitigate image artifacts due to heterogeneous acoustic properties of an object. Reconstructed images and numerical results produced from simulated and experimental TAT measurement data are employed to demonstrate these effects.     

激光反射层析成像技术的研究进展

激光反射层析成像技术是一种通过不同角度下激光在物体深度方向的一维时间流信号积分重建目标二维轮廓图像的远距离成像技术,其重建图像的空间分辨率只与探测器的带宽、激光的脉冲宽度和噪声有关,与作用距离、光学接收孔径无关,是现阶段实现远距离空间目标探测的最可行手段。介绍了激光反射层析成像的基础理论问题、投影数据处理方法、图像重建算法、探测成像实验系统以及成像实验研究等问题,总结和对比了国内外的研究进展,探讨了需要重点解决的问题,并展望了激光反射层析成像技术未来的研究方向。     

耦合式背光介观荧光分子成像系统设计北大核心CSCD

在生物组织工程的应用中需要有对生物结构标记的三维、纵向评估。一般来说,这些生物组织的结构通常是几毫米厚和浑浊的,因此对图像成像有很大挑战性,且经典荧光显微技术不能满足于其需要。介观荧光分子成像系统是一种新兴的成像系统,该系统基于介观荧光分子层析方法,它填补了显微荧光分子成像技术和宏观荧光分子成像技术之间的空白。为提升介观荧光分子重建的性能,本文主要基于光学原理对光学系统的配置参数进行了优化和改进,包括探测器布局、非耦合或耦合的扫描模式,并对介观荧光分子成像系统的三维成像性能进行了评价和对比。结果表明,本文设计的耦合式背光介观荧光分子层析成像(mesoscopic fluorescence molecular tomography imaging,MFMT)系统能够很好地提升重建性能,获得高质量的重建结果。     

Imaging with LINC-NIRVANA

The basic problem of LINC-NIRVANA (LN) imaging is to combine the different images for getting a single image, possibly with a resolution close to that of a 22.8 m mirror in all directions. This result can be hardly reached in practice because it depends on the level and uniformity of the adaptive optics (AO) correction and on the declination of the scientific target, controlling the orientations of the baseline that can be used during its observation. In this article, we give a brief introduction to this problem. It can be solved by iterative methods related to the well-known Richardson-Lucy (RL) algorithm. Since RL is a particular case of the maximum likelihood method introduced by Shepp and Vardi in emission tomography and denoted expectation maximization (EM), improvements of EM, proposed in the field of medical imaging can be applied to LN.     

Multimodality Radionuclide, Fluorescence, and Bioluminescence Small-Animal Imaging

The imaging of molecular events in the complex physiological interplay between organelles, cells, tissues, and organs in the whole organism is now more practical through the use of small-animal imaging technologies. Radionuclide based molecular imaging using single photon emission computed tomography (SPECT) and positron emission tomography (PET) scanners have been used for imaging intracellular enzymes, receptors, transporters, reporter gene expression, and cell trafficking in small animals such as mice and rats. Sensitive cooled charge-coupled device (CCD) cameras which detect emitted light from fluorescent and bioluminescent probes within an organism have been useful in imaging pathologic changes in diseases such as cancer and infectious disease in small-animal models. Each molecular imaging modality has differing strengths and weaknesses. However, the ability to generate molecular reporter strategies that can be applied in multiple detection systems will likely provide more robust imaging data sets than from any single modality. The ultimate function of multimodality reporter strategies will be to provide information about molecular targets in a continuum of research subjects from cells to small animals to human patients.     

Fourier transform nuclear magnetic resonance tomographic imaging

Nuclear Magnetic Resonance (NMR) tomographic imaging is a newly emerging, noninvasive, three-dimensional (3-D) imaging technique. Although similar to the well known X-ray Computerized Tomography (X-CT), it uses magnetic fields and RF signals to obtain anatomical information about the human body as cross-sectional images in any desired direction, and can easily discriminate between healthy and abnormal tissues. This new technique is an interdisciplinary science which encompasses the latest technologies in electrical, electronics, computers, physics, chemistry, mathematics, and medical sciences. Principles of this new technique known as "Fourier transform nuclear magnetic resonance imaging" or simply "NMR imaging" are reviewed from the physics and engineering points of view to provide basic concepts and tools, which, hopefully, will be useful for the future development of this exciting new field. Along with the review of the basic principles and methods involved in NMR tomography, computer simulations and modelings are presented to clarify the complexity of the NMR imaging method and provide an insight into the method, especially image-formation aspects and processing, the central theme of NMR tomography. In this paper, four main types of imaging methods-namely, line-scan imaging, direct Fourier-transform (Kumar-Welti-Ernst method) imaging, line-integral projection reconstruction, and plane-integral projection reconstruction, as well as the possibility of relaxation time imaging, are discussed in detail Methods of improving performance with respect to the statistical aspects of image quality and imaging times are also discussed.     

From Genomics to Clinical Molecular Imaging

Molecular imaging, as applied to clinical practice today, is in its early stages. Encouraging advances achieved in clinical positron emission tomography (PET) and small-animal imaging indicate that this technique is evolving into an indispensable diagnostic tool. When employed with complementary morphological imaging procedures, molecular imaging results in substantial diagnostic capability. It will enable the physician to unveil topographic biochemistry in situ and reduce invasive testing. While this is at least in part futuristic, it is clear already today that a comprehensive set of imaging modalities will be required. Imaging modalities most appropriate for molecular imaging are PET, single photon emission computed tomography (SPECT), magnetic resonance imaging (MRI), optical imaging, and ultrasound. The foundation for advances in molecular imaging, however, is not primarily imaging hardware development but scientific advancements in molecular biology and progress in probe development. Other factors to consider are postprocessing software and, inevitably, market dynamics. Thus. it implies efficient collaborations across disciplines, agencies, and industries to develop molecular imaging tools for the clinic.     

光学相干层析成像技术确定组织光学特性

光学相干层析成像(OCT)是近年来发展较快的一种新型成像技术,能对生物组织内部的微观结构进行高分辨率的横断面层析成像,具有快速、非侵入及高分辨率等特点,在体生物组织微观结构分析和疾病诊断等方面具有重要的应用价值.综述了采用光学相干层析成像技术确定生物组织光学特性的研究.     

Three-Dimensional Microwave Breast Imaging: Dispersive Dielectric Properties Estimation Using Patient-Specific Basis Functions

Breast imaging via microwave tomography involves estimating the distribution of dielectric properties within the patient's breast on a discrete mesh. The number of unknowns in the discrete mesh can be very large for 3-D imaging, and this results in computational challenges. We propose a new approach where the discrete mesh is replaced with a relatively small number of smooth basis functions. The dimension of the tomography problem is reduced by estimating the coefficients of the basis functions instead of the dielectric properties at each element in the discrete mesh. The basis functions are constructed using knowledge of the location of the breast surface. The number of functions used in the basis can be varied to balance resolution and computational complexity. The reduced dimension of the inverse problem enables application of a computationally efficient, multiple-frequency inverse scattering algorithm in 3-D. The efficacy of the proposed approach is verified using two 3-D anatomically realistic numerical breast phantoms. It is shown for the case of single-frequency microwave tomography that the imaging accuracy is comparable to that obtained when the original discrete mesh is used, despite the reduction of the dimension of the inverse problem. Results are also shown for a multiple-frequency algorithm where it is computationally challenging to use the original discrete mesh.