Three-Dimensional Monochromatic X-ray CT

研究了新一代三维单色X射线CT的发展。锥束CT可以实现由二维投影数据直接进行三维重建。研究结果如下：1.基于数学精确重建的完备性条件，在三维CT系统结构中，采用了正交圆-线轨道作为最有希望的X射线源扫描方法。从三维Radon变换的反演公式出发，以实际可实现的形式推导出了数学上精确的三维CT图像重建算法。计算机仿真研究验证了所提出的扫描方法和所推导出的重建算法的有效性。…高能物理国家实验室利用同步辐射产生的荧光X射线建立了三维单色X射线CT原型机系统筑波有更多报道。白光照射靶材料后产生的荧光X射线具有大的束流面积和空间均匀的光强分布，其能量可通过改变靶材料来调节。该物体安装在模拟圆、线轨迹扫描的计算机控制装置上，通过像增强器采集二维投影数据。在该实验系统中可以实现物体三维结构的完整重建。利用可调谐X射线源的良好特性，对特定材料(如对比剂材料)的K吸收边上下的图像进行减法重建。该可视化软件可以直观地显示物体的三维结构。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，这降低了图像质量。如果我们能够解决这个问题，由于没有射束硬化，就可以获得组织的CT值绝对值的三维图像。较少

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