Three-Dimensional Monochromatic X-ray CT

三维单色x射线CT是新一代CT的发展方向。锥束CT可以实现二维（2-D）投影数据的直接三维重建。通过调查可以得出以下结论：1。基于数学精确重建的完备性条件，采用正交圆线轨道作为三维CT系统构型中最有前途的x射线源扫描方法。从三维Radon变换的反演公式出发，导出了数学上精确的三维CT图像重建算法。计算机仿真研究证明了所提出的扫描方法和推导的重建算法的有效性。在筑波国家高能物理实验室建立了利用同步辐射产生的荧光x射线进行三维单色x射线CT实验的原型系统。用白色x射线照射目标材料所产生的荧光x射线，产生光束面积大、强度空间均匀的锥束几何形状，其能量可通过改变目标材料来调节。该物体安装在计算机控制的模拟圆线轨道扫描装置上，通过图像增强器获取二维投影数据。该实验系统可以实现物体三维结构的完整重建。利用可调x射线源的理想特性，通过对材料k吸收边缘上下的图像进行相减，重建特定材料（例如造影剂）的三维图像。利用可视化软件可对物体的三维结构进行可视化。在锥束数据采集方案中最严重的问题是光子在组织中的散射，从而降低图像质量。如果我们能解决这个问题，由于没有光束硬化，就可以获得具有组织绝对CT值的三维图像。少

The development of three-dimensional (3-D) monochromatic X-ray CT has been investigated as a new generation CT.Direct reconstruction in 3-D from two-dimensional (2-D) projection data can be achieved by cone-beam CT.The following findings could be obtained through the investigation as ;1. Based on the completeness condition for mathematically exact reconstruction, an orthogonal circle-and-line orbit has been adopted as the most promissing scanning method of X-ray source in 3-D CT system configuration.2. The mathematically exact 3-D CT image reconstruction algorithm has been derived from the inversion formula of 3-D Radon transform in the practically implementable form.3. Computer simulation studies have demonstrated the validity of the proposed scanning method and the derived reconstruction algorithm.4. A proto type experimental system of 3-D monochromatic X-ray CT using fluorescent X-rays generated by synchrotron radiation was constructed in National Laboratory for High Energy Physics … More in Tsukuba. The fluorescent X-rays generated by irradiating the target material with a white X-ray produce a cone-beam geometry with large beam area and spatially uniform intensity, and its energy is tunable by changing the target materials.5. The oject is mounted on the computer controlled device which simulates the scanning of circle-and-line orbit, and 2-D projection data is acquired by the image intensifier. The complete reconstruction of 3-D structure of object could be achieved in this experimental system.6. Using the desirable characteristic of tunable X-ray source, 3-D image of specific materials (for example contrast materials) is reconstructed by taking subtraction between images above and below K-absorption edge of materials. The 3-D structure of object can be visualized by the visualization software.7. The most serious problem in the cone-beam data collection scheme is the scattering of photons in tissue which degrades the image quality. If we can resolve this problem, 3-D image with absolute CT value of tissue is available because of the absence of beam hardening. Less