Elimination of nonpivotal plane images from x-ray motion tomograms

A method for eliminating the contribution of nonpivotal plane images into a conventional X-ray motion tomogram is described. A set of tomograms, each focused on one of distinct parallel planes, are combined to form a blur-free tomogram. From the mathematical analysis of conventional tomography, it is found that the multisection tomography system reduces to a three-dimensional incomplete linear system with angularly limited frequency response. An iterative constrained reconstruction algorithm incorporating the object boundary constraint is used for reconstruction of a blur-free tomogram without a contribution from nonpivotal planes. Some computer simulations were made for verification of the algorithm. Although the algorithm accomplishes the three-dimensional reconstruction of volume rather than image restoration of a single slice plane, the optimal high-pass spatial filter applying to a single tomogram is derived on the way to solving the inverse problem of the multisection tomography system.     

Weighted expectation maximization reconstruction algorithms for thermoacoustic tomography

Thermoacoustic tomography (TAT) is an emerging imaging technique with potential for a wide range of biomedical imaging applications. In this correspondence, we propose an infinite family of weighted expectation maximization (EM) algorithms for reconstruction of images from temporally truncated TAT measurement data. The weighted EM algorithms are equivalent mathematically to the conventional EM algorithm, but are shown to propagate data inconsistencies in different ways. Using simulated and experimental TAT measurement data, we demonstrate that suitable choices of weighted EM algorithms can effectively mitigate image artifacts that are attributable to temporal truncation of the TAT data function.     

Fast circular tomography device for cardiac imaging: image deflection mechanism and evaluation

A circular tomography system for cardiac imaging is described and measurements of the detector system are presented. Fast tomographic motion is obtained with a custom-made rotating focal spot X-ray tube combined with servo-operated scanning mirrors that deflect the optical image between a large field of view image intensifier and television camera. The motion of the deflection mirrors is locked in frequency and phase to the position of the focal spot with precision analog electronics. Initial measurements on the system components indicate that circular tomograms of the beating heart can be obtained in 1/60 s at rates as high as 30/s. Image degradation due to focal spot tracking error is minimal; however, the optical temporal lag of a P-20 type image intensifier output phosphor results in a factor of three contrast loss for millimeter-sized objects. A linear system analysis in conjunction with the measured temporal step response of the phosphor is in good agreement with the magnitude of this contrast loss.     

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.     

Design and implementation of digital tomographic filters

A technique is proposed which allows the selective filtering of conventional radiographs in order to obtain depth-dependent information by utilizing the depth-dependent information contained therein. This technique, referred to as tomographic filtering or tomographic filtration process (TFP), takes advantage of the finite size of the X-ray source, so that after processing, the image of a particular layer is improved while the others are not. This paper starts with a brief review of technique and then concentrates on the design and implementation of digital tomographic filters. Examples are shown, including images of simulated radiographs processed with such filters. Evaluations of the performance of these filters show that the image quality cannot be as good as that of standard tomography or multiprojection reconstruction techniques; nevertheless they represent an improvement over conventional radiology, and highlight additional depth-dependent information contained in radiographs. This paper concludes with suggestions for further research in this area.     

Digital tomographic filtering of radiographs

Conventional radiographs do not provide information about the depths of details and structures because they are two-dimensional projections of three-dimensional bodies. Taking advantage of the finite size of the X-ray source and the divergent nature of the X-ray beam, a radiograph can be processed by two-dimensional digital filtering techniques, so that the image of a particular layer is improved, while the others are degraded. This technique is referred to as a tomographic filtration process (TFP). This paper develops the mathematical and physical foundations of the method. Based on a model of the radiologic process, which is described in the paper, the equations of image formation in standard tomography, conventional radiography, and tomographic filtering are derived and compared.     

Evaluation of digital tomographic filters

Recently, a technique has been proposed to filter conventional radiographs in order to obtain depth-dependent information by simulating standard tomography. This technique has been referred to as tomographic filtering or tomographic filtration process (TFP). It takes advantage of the finite size of the X-ray source, so that after processing the image of a particular layer is improved, while the others are degraded. This paper briefly reviews this technique and then concentrates on its analytical evaluation. A comparative assessment of tomographic filtering is produced taking as benchmarks two well established radiologic procedures: standard tomography and conventional radiology. The comparison is made on the basis of the following evaluation criteria: the exposure angle, the thickness of the cut, the rate of change of the transfer function, the signal-to-noise ratio, and the radiation dose. Practical evaluations are also shown.     

基于PCI的高分辨率医用X光视频图像采集及处理系统

采用影像增强器 CCD采集方式实现了高分辨率X光医学视频图像采集与处理系统.系统包括三大模块:视频图像采集部分、图像数据传输部分和图像后处理部分.硬件电路采集的数字图像通过高速PCI总线与PC机进行视频图像数据传输,再由图像处理软件对图像作后续处理;软件包括PCI设备驱动程序以及图像后处理软件平台,采用Microsoft的Visual C 6.0语言编写.本文详细描述了X射线医学视频图像采集与处理系统工作原理和工作过程,重点阐述在基于Windows平台的PCI设备驱动程序编制过程中碰到的关键问题。在医学图像数字化采集及传输方面作了有效的探索并取得了一定的成果,具有普遍的应用意义.     

Image restoration in computed tomography: estimation of the spatially variant point spread function

An indirect method for determining the point-spread-function (PSF) in computed tomography (CT) is described. Unlike experimental techniques in which a resolution phantom is scanned to obtain the system PSF, the approach estimates the parameters of a model which describes the two-dimensional X-ray beam profile at each point as a convolution of the appropriately scaled focal spot intensity and detector sensitivity distributions. The model was validated by experimental measurement of the focal spot intensity distribution. Using known X-ray beam profiles, the PSF of a CT scanner can be derived by simulating the data collection process and applying conventional image reconstruction techniques. Visual comparison of directly measured and computed PSFs reveals an asymmetry resulting from misregistration of the phantom wires and the image grid.     

Image guidance of endovascular interventions on a clinical MRscanner

Magnetic resonance imaging (MRI) offers potential advantages over conventional X-ray techniques for guiding and evaluating vascular interventions. Image guidance of such interventions via passive catheter tracking requires real-time image processing. Commercially available MR scanners currently do not provide this functionality. This paper describes an image processing environment that allows near-real-time MR-guided vascular interventions. It demonstrates (1) that flexibility can be achieved by separating the scanner and the image processing/display system, thereby preserving the stability of the scanner and (2) that sufficiently rapid visualization can be achieved by low-cost workstations equipped with graphics hardware. The setup of the hardware and the software is described in detail. Furthermore, image processing techniques are presented for guiding the interventionalist through simple vascular anatomy. Finally, results of a phantom balloon angioplasty experiment are presented     

Exact frequency-domain reconstruction for thermoacoustic tomography--II: Cylindrical geometry

Microwave-induced thermoacoustic tomography (TAT) in a cylindrical configuration is developed to image biological tissue. Thermoacoustic signals are acquired by scanning a flat ultrasonic transducer. Using a new expansion of a spherical wave in cylindrical coordinates, we apply the Fourier and Hankel transforms to TAT and obtain an exact frequency-domain reconstruction method. The effect of discrete spatial sampling on image quality is analyzed. An aliasing-proof reconstruction method is proposed. Numerical and experimental results are included.     

Geophysical imaging with arbitrary source illumination

Geophysical diffraction tomography is a technique for quantitative, high-resolution, subsurface imaging. This approach to imaging is a generalization of the conventional backprojection algorithm of X-ray tomography accounting for the diffraction effects that result from longer wavelength seismic or electromagnetic waves necessary for geophysical remote sensing. A diffraction tomography algorithm is presented for a configuration in which a finite number of sources of arbitrary character are distributed along one line and a finite number of receivers are distributed along a line having an arbitrary orientation with respect to the source line. Since most geophysical sources may be reasonably represented as point sources, the two-dimensional form of the algorithm is implemented for cylindrical-beam (a point source in two dimensions) illumination. Numerical experiments are performed to investigate a range of source-receiver configurations. It is found that parallel source and receiver arrays, a cross-borehole configuration, provide better image quality than orthogonal arrays     

X-Ray Backscatter Imaging

This paper describes a new type of X-ray Compton scatter imaging technique which has potential application to medical diagnostic radiography. This system detects the Compton interacted radiation which is scattered back toward the X-ray source and uses the information to generate an interior view of an object from a frontal backprojection imaging perspective. X-ray scatter radiographs can provide a three-dimensional imaging ability that is different from computerized axial tomography and may provide additional medical diagnostic information which is difficult or expensive to derive from conventional techniques.     

Processing of X-ray images

A review of three aspects of image processing of X-ray imagery is presented. Short reviews of computer assisted tomography and coded aperture imaging are given. The application of image enhancement and restoration to radiography is reviewed in greater depth.     

Gray-Scale Image Coding for Freeze-Frame Videoconferencing

A new gray-scale image coding technique has been developed, in which an extended DPCM approach has been combined with entropy coding. This technique has been implemented in a freeze-frame videoconferencing system which is now operational at IBM sites throughout the world. Following image preprocessing, the two fields of the interlaced 512 x 480 pixel video frame are compressed sequentially with different algorithms. The reconstructed image quality is improved by subsequent image postprocessing, the final reconstructed image being almost indistinguishable from the original image. Typical gray-scale video images compress to about a half bit per pixel and transmit over 4.8 kbit/s dial-up telephone lines in about a half minute. The gray-scale image processing and compression algorithms are described in this paper.     

单分子荧光涨落系统的研制

报道一种单分子荧光涨落检测系统的实验装置的设计。该系统主要由激光共焦系统、微区激发系统、光电转换及数据采集和分析系统组成。本文另对共焦系统和数据采集系统的原理作了简要的说明。由于采用了共焦系统，这样就可以从一个视场深度比较窄的区域内采集生物信息，而不需要象普通荧光采集系统那样大范围采集，焦点外的荧光信号进行检测，这些工作也为在单分子水平上探索疾病机理和揭示生命现象的本质提供了一个有力的手段。     

Statistical approach to X-ray CT imaging and its applications in image analysis. II. A new stochastic model-based image segmentation technique for X-ray CT image

For pt.I, see ibid., vol.11, no.1, p.53.61 (1992). Based on the statistical properties of X-ray CT imaging given in pt.I, an unsupervised stochastic model-based image segmentation technique for X-ray CT images is presented. This technique utilizes the finite normal mixture distribution and the underlying Gaussian random field (GRF) as the stochastic image model. The number of image classes in the observed image is detected by information theoretical criteria (AIC or MDL). The parameters of the model are estimated by expectation-maximization (EM) and classification-maximization (CM) algorithms. Image segmentation is performed by a Bayesian classifier. Results from the use of simulated and real X-ray computerized tomography (CT) image data are presented to demonstrate the promise and effectiveness of the proposed technique.     

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.     

Computed tomographic imaging of the coronary arterial tree-use of local tomography

It has been demonstrated previously (see E.L. Ritman and A.A. Bove, in State of the Art in Quantitative Coronary Arteriography, p.67-78, 1986) that coronary artery anatomy can be visualized using high-speed, volume-scanning X-ray CT (computed tomography). In the current study it is demonstrated that local image reconstruction (i.e. the reconstruction kernel is ~2(+) mm long), as distinct from more conventional global image reconstruction (i.e. 200(+) mm kernel length), has the advantage of reducing the need for operator interactive image processing. In addition, the local reconstruction algorithm eliminates the need for recording the X-ray projection data over the full transaxial extent of the thorax because it requires only the X-ray attenuation data over the region of the heart. This latter aspect reduces the dynamic range requirements for the sensors and could reduce total X-ray exposure.     

一种基于DSP和FPGA的图像处理系统

设计了一种以FPGA为数据采集逻辑控制单元,以DSP为高端图像处理单元的数字图像处理系统。介绍了该系统的硬件组成、工作原理。从视频编码单元、图像处理单元和视频输出单元对整个系统的构成和设计进行了描述,分析了系统设计时的各个关键技术环节。