Propagation-based phase-contrast imaging was simulated based on paraxial Fresnel-Kirchoff diffraction integral and spherical wave illumination. Under a developed micro-CT system parameters, the effects of focal-spot size and imaging geometry on phase-contrast imaging have been investigated using a 2 mm thickness polystyrene edge phantom. An equivalent mono-energy was used to substitute the polychromatic spectrum of the micro-focus x-ray source. To consider effects of focal-spot size and detector resolution, the obtained phase-contrast image with an ideal point source was convolved with source intensity distribution and point spread function of detector. Simulations show reasonable influences of the two parameters and are in good agreement with experimental results.

This paper presents a novel electron optical simulation design for a carbon nanotube (CNT) based field emission X-ray source. The CNT cathode consists of an elliptical emission surface, which enables the focusing of an isotropic X-ray beam. A novel type electrostatic lens design with non-rotationally symmetric focusing aperture, elliptical or rectangular aperture, is presented. The simulation results indicate that our proposed design is capable of providing large and approximately equal demagnification factors along both short and long axis of the emission surface.

X射线探测器的调制传输函数(MTF)可以有效反映X射线摄影系统的成像质量,是客观评价X射线成像系统性能的一个重要方法.实验采用一个缝宽为10μm的狭缝相机和一个微焦斑X射线源,搭建测量平板探测器MTF曲线的平台.通过探测器采集X射线穿透狭缝的成像数据,运用MAT-LAB编程对狭缝图像进行线扩展函数(line spread function,LSF)的合成、高斯拟合、去噪、傅立叶变换和归一化等处理,得到探测器的MTF曲线,再利用MTF曲线定量分析探测器的成像性能.通过探测器采集不同的X射线源电压、发射功率、狭缝倾角及曝光时间下的数据,比较它们对探测器MTF测量结果的影响.

Most existing x-ray sources use hot cathodes with high working temperature and high power con-sumption are difficulty to realize the integration of multiple cathodes.Our laboratory developed cold cathode field emission x-ray system based on carbon nanotube.It can avoid this defect of the traditional hot cathode. At the same time, it provides a new path to enhance highly time-resolved performance and reduce radiation dose for CT system.Therefore, the CNT field emission x-ray measurement and control system is developed based on the LabVIEW software aimed at testing the sample of CNT cathode performance, this system proves to realize stable and reliable operation, high automatic measure and convenient operation, thus be able to program-matically control X-ray source and provide a reliable measurement and control platform for developing stable CNT cathode emission current, improving the anode voltage and the material aging effect.

Based on its region-of-interest (ROI) reconstruction advantage, backprojection-filter algorithm has been used in cone-beam CT recently. However, because of its complexity and computation, there is memory insufficiency in the implementation of GPU acceleration. Hence, CUDA-based parallel implementation for BPF algorithm was proposed. Meanwhile, an accelerated projection scheme and other accelerated techniques were included as well, such as features of BPF for acceleration. Besides, video memory pool was introduced to optimize the implementation. With an efifcient structure, the simulation results show that it takes only 8.055 seconds by using the new structure to reconstruct 512×512×512 data and only 4.566 seconds for the ROI reconstruction. The output of ifrst block data takes only 1.523 seconds. With a great decrease of memory occupation from 2.5 GB to less than 100 MB, the new scheme is suitable for big data reconstruction.

Cone-beam dental computerized tomography has been introduced as a system geared towards maxillofacial imaging, which is gradually becoming a common tool within the dental industry. Segmentation of teeth from dental CT data is vital for a variety of computer-aided procedures such as dental implants, orthodontic planning and cosmetic surgeries. Teeth segmentations near soft tissue structures can help clinicians to assess the quality of a patient's teeth more easily. Moreover, the ability to identify particular regions surrounding teeth can help to provide better image results generated using 3D surface/volume rendering techniques. This paper, presents an experimental study for teeth segmentation employing two different thresholding techniques. The performances of these techniques are compared with each other. The experimental results show that there is a noticeable difference in segmentation quality between the two methods presented in this paper.

In the past decade, phase-contrast imaging (PCI) has become a hot research with an increased improvement of the image contrast with respect to conventional absorption radiography. In this paper, effects of tube voltage (kVp) on propagation-based phase-contrast imaging have been investigated with two types of microfocus x-ray tubes, a conventional sealed x-ray tube with the focal spot size of 13-20 μm and an open x-ray tube with minimum focal spot size less than 2 μm. A cooled x-ray CCD detector with the pixel size of 24 μm was used to acquire digital images. Two thin plastic sheets with different thickness were used as radiography phantoms. Two different phenomena were observed for the two x-ray tubes, for the open tube, phase-contrast effect has a slight drop with the increasing of tube voltage, however, it is opposite for the sealed tube. A further investigation indicates that the variation of focal spot size causes the abnormal result for the sealed tube. It also shows that phase-contrast effect is more sensitive to focal spot size than tube voltage.

Dental CT is the most appropriate and accurate device for preoperative evaluation of dental implantation. It can demonstrate the quantity of bone in three dimensions (3D), the location of important adjacent anatomic structures and the quality of available bone with minimal geometric distortion. Nevertheless, with the rapid increase of dental CT examinations, we are facing the problem of dose reduction without loss of image quality. In this work, backprojection-filtration (BPF) and Feldkamp–Davis–Kress (FDK) algorithm was applied to reconstruct the 3D full image and region-of-interest (ROI) image from complete and truncated circular cone-beam data respectively by computer-simulation. In addition, the BPF algorithm was evaluated based on the 3D ROI-image reconstruction from real data, which was acquired from our developed circular cone-beam prototype dental CT system. The results demonstrated that the ROI-image quality reconstructed from truncated data using the BPF algorithm was comparable to that reconstructed from complete data. The FDK algorithm, however, created artifacts while reconstructing ROI-image. Thus it can be seen, for circular cone-beam dental CT, reducing scanning angular range of the BPF algorithm used for ROI-image reconstruction are helpful for reducing the radiation dose and scanning time. Finally, an analytical method was developed for estimation of the ROI projection area on the detector before CT scanning, which would help doctors to roughly estimate the total radiation dose before the CT examination.

Micro-CT is a new three dimensional imaging tool based on x-ray imaging mechanism and with ultrahigh spatial resolution. It can be used to image all kinds of samples or live small animalsunder non-destructive condition. In this paper, a micro-CT prototype system with high spatial resolution was developed. From the projective images and reconstructed cross-sectional images of a small insect sample, the phase-contrast effect with the edge-enhancement trait can be observed clearly. The cross-sectional images also show that the developed micro-CT system has the detail detectability down to 12 micrometers.

Carbon nanotube(CNT) cathode based field emission X-ray source and imaging techniques as an important development for X-ray CT technology,has generated much interest in recent years.Compared to the more traditional thermal emission X-ray source,CNT X-ray source possesses several desirable attributes such as miniaturization,fast response time,efficient-focusing and improved control of emitted electrons.Thus,an imaging tool based on these attributes will contribute significantly to the field of X-ray imaging within both medicine and industry.In this paper,the development of CNT cathode based X-ray source and imaging methodologies will be discussed.

Carbon nanotube(CNT) cathode based X-ray source is a leading field of X-ray CT technology in recent years.Compared with traditional thermal emission X-ray source, CNT X-ray source has characteristics of miniaturization, high resolution of time and programmable emission. Multi-beam X-ray source for stationary X-ray scanner is one of the most important applications of CNT X-ray source. In this paper, the development of CNT cathode based multi-beam X-ray source were introduced.

A mathematical derivation was conducted to illustrate that exact 3D image reconstruction could be achieved for z-homogeneous phantoms from data acquired with 2D general trajectories using the back projection filtration (BPF) algorithm. The conclusion was verified by computer simulation and experimental result with a circular scanning trajectory. Furthermore, the effect of the non-uniform degree along z-axis of the phantoms on the accuracy of the 3D reconstruction by BPF algorithm was investigated by numerical simulation with a gradual-phantom and a disk-phantom. The preliminary result showed that the performance of BPF algorithm improved with the z-axis homogeneity of the scanned object.

Conventional CT reconstruction algorithm, filtered-backprojection (FBP), requires the projection data acquired within the angular range from 0 to 2pi. However, for an irregular object, the data acquired at some projection views may be not available due to the detector saturation. In this work, we proposed a method to optimize the current patterns for obtaining two sets of complementary attenuation data and to employ an iterative method based on equation and inequality to improve the reconstruction quality. The simulation results obtained from the projection data, which are generated by use of the GEANT toolkit, show that the uses of optimal current scanning method and the corresponding iterative reconstruction method can yield the accuracy images with lower noise level.

Based upon a bench-top micro-CT system, propagation-based phase-contrast imaging has been investigated using insects and a thin plastic sheet. The system mainly includes a micro-focus source with focal spot size of 13–20μm and a cooled X-ray CCD detector with pixel size of 24μm. The edge-enhancement effect can be found clearly in the acquired images. With a 0.5mm thickness plastic edge phantom, the effects of X-ray tube voltage and imaging geometry on the phase-contrast imaging were investigated, and quantitative index, edge-enhancement index (EEI), were also calculated. In our study, an interesting phenomenon was observed that the phase-contrast effect becomes more pronounced as the tube voltage increases from 20kVp to 90kVp. Further investigation indicates that smaller focal spot size resulting from the reduction of tube current at higher tube voltage, has caused the unexpected phenomenon. Inferred from our results, phase-contrast effect is insensitive to the tube voltage in the range of 20–90kVp (widely used in medical diagnosis); however, it is sensitive to the focal spot size. In addition, for the investigation of the effect of imaging geometry, an optimal geometric magnification range of 2.5–4.5 is suggested to get a good phase-contrast imaging for a micro-CT system with source-to-detector distance of 720mm.

Medical visualization refers to the techniques and processes used to create images of the human body for clinical purposes or medical science including the study of normal anatomy and physiology. The visualization of medical images data sets is to reconstruct 3D images with the 2D slice images so as to reveal the 3D configuration of organs through human visual system. Visual C++ are used to reconstruct 3D images using the CT slice sequence. The key algorithms and human CT 3D visualization results are given in this paper. The coordinates can be acquired by the mouse clicking in the 3D space, by which to realize the point coordinate acquisition of the 3D medicine images. The visualization of medical images can provide us with more information and means of visual interactive for simulated operations and assistant diagnosis. The technique can realize the real time interaction quantitative measurement of three-dimensional CT image.

Three-dimensional medical image visualization becomes an essential part for medical field,including computer aided diagnosis,surgery planning and simulation,artificial limb surgery,radiotherapy planning,and teaching etc.In this paper,marching cubes algorithm is adopted to reconstruct the 3-D images for the CT image sequence in DICOM format under theVC++6.0 and the visual package VTK platform.The relatively simple interactive operations such as rotation and transfer can be realized on the platform.Moreover,the normal vector and interior point are calculated to form the virtual clipping plane,which is then used to incise the 3-D object.Information of the virtual slice can be obtained,in the mean while the virtual slice images are displayed on the screen.The technique can realize the real time interaction extraction of virtual slice on 3-D CT image.The cuboids structured can be zoomed,moved and circumrotated by operating mouse to incise the 3-D reconstruction object.Real time interaction can be realized by clipping the reconstruction object.The coordinates can be acquired by the mouse clicking in the 3D space,to realize the point mouse pick-up as well angle and distance interactive measurement.We can get quantitative information about 3-D images through measurement.

Micro-CT with a high spatial resolution in combination with computer-based-reconstruction techniques is considered a powerful tool for morphological study of insects. The quality of CT images crucially depends on the precise knowledge of the scan geometry of the micro-CT system. In this paper, we have proposed a method to calculate the deviation of rotating axis for compensating deficiency of existing methods. A practical application of this geometric calibration method of the micro-CT system for insect imaging is presented. We have performed the computer-simulation study and experimental study with our prototype micro-CT system. The results demonstrate that the proposed technique is accurate and robust. In addition, we have evaluated the imaging characteristics of the detector in terms of modulation-transfer function (MTF). Finally, insect imaging performance and image reconstruction from data acquired with different energies are presented.

Micro-computed tomography (Micro-CT) is a new three-dimension high-resolution imaging device based on X-ray imaging principle. Precise assessment of the micro-CT system's geometric parameters is crucial to achieve successful reconstruction with good spatial resolution and low artifact content in the reconstructed tomography images. Noo et al. (2000) have proposed a new analytic method for calibration of X-ray cone-beam scanners that use a circular path for the cone vertex. In this paper, we use this analytic calibration method for the estimation of the geometric parameters of a practical small-animal imaging micro-CT system. We improve calibration phantom of this method in order to make it more suitable for micro-CT system. An accurate determination of system geometric parameters results from the proposed method. The projection images demonstrated that the adopt method is robust and easy to implement with high precision. The overall performance of the micro-CT system is demonstrated in some results of small-animal imaging.

Medical image analysis is more than just algorithms. Visualization of the original image data and processed results, interaction with the data, as well as the data themselves are also important. Medical image 3D visualization is one of the fundamental processes in medical diagnostics. Using the acquired 3D images it is possible to find the volume of pathology zone, which is the evidence of a specific disease. In this paper, we realized three-dimensional visualization of blood vessel of brain and skeleton from non-enhanced MR angiography and CT data. VC++ 2008 with VTK toolbox are used to reconstruct 3D images using the MR and CT slice sequence in DICOM format. The key algorithms, blood vessel of brain and human skeleton 3D visualization results are given. Furthermore, more complex interaction methods including mouse pick-up, angle and distance quantitative measure in space on 3D MR and CT images can be realized. The coordinates can be acquired by the mouse clicking in the 3D space, by which to realize the point mouse pick-up as well angle and distance interactive measure of the 3D medicine images. We can get quantitative information about 3D images through measurement. The methods can assist doctors to make better and more accurate diagnosis.

Small-animal imaging technology has been rapidly developed for longitudinal screening of laboratory animals raised with disease developments or genetic manipulations. Micro-CT is a noninvasive imaging modality used to assess morphology and function in small-animal imaging. Geometric calibration involves the estimation of a set of parameters that describes the geometry of such systems, and is essential for accurate image reconstruction. Noo F et al (2000) have proposed a new analytic method for calibration of x-ray cone-beam scanners that use a circular path for the cone vertex. In this paper, we use this analytic calibration method for the estimation of the geometric parameters of a practical small-animal imaging micro-CT system. We improve calibration phantom of this method in order to make it more suitable for micro-CT system. The overall performance of the micro-CT system is demonstrated in some results of small-animal imaging. The projection images demonstrated that the adopt method is robust and easy to implement with high precision.