Study on Artifact occurredin the X-ray CT Image due to the Motion of the Object

(1)在X射线计算机断层摄影（CT）中，必须允许扫描物体的时间以获得其投影数据。如果物体在扫描过程中是不稳定的，它的重建图像将包含称为“运动”的误差。近年来，在临床实践中发现了两种运动伪影，即“模糊像”和“频闪像”，需要对其进行理论分析。假设物体是刚体，其运动可分为旋转运动和平行运动。分析了刚体旋转运动引起的重建图像质量下降和伪影。利用点扩散函数，研究了任意形状刚体旋转引起的CT图像质量下降问题。分析了刚性物体在CT中由于旋转而产生的模糊图像的特点和频闪图像的形状。用线光源解释了产生风暴像的原因。理论已经被证实 ...更多信息 通过计算机模拟。(2)康普顿散射成像可以显示给定物体的电子密度，这对于医学诊断可能是重要的。然而，该技术的临床应用尚未开发，因为由于多种原因无法获得清晰的图像。康普顿散射不可避免地使图像受到多次散射的严重污染。除非仔细处理多次散射，否则不能正确获得物体小区域内的电子密度。本文讨论了康普顿散射成像系统中多次散射的消除方法。用通用蒙特卡罗程序EGS 4模拟了入射光子与物体内部物质相互作用的过程。模拟进行了使用一个水球体模与半径为10厘米的单色X射线在100 keV的光束照射。散射光子从体模发射的观察和单康普顿散射从一个焦点的量的比率计算的多个scatterong。为了提高图像质量，消除康普顿散射中的多次散射是必不可少的。为此，提出了θ和φ准直器和能量窗口，并通过模拟定量地估计了它们的效果。结果表明，通过在成像系统中引入所提出的方法，康普顿散射信号与多次散射噪声的比值S/N可以从0.022提高到40。数值模拟得到的定量结果对实际康普顿散射成像系统的设计有一定的指导意义。少

(1) In the X ray computed tomography (CT), time to scan an object must be allowed to obtain its projection data. If the object is not steady during the scanning, itsu reconstructed image would contain errors called "mottifacts. Recently , two kinds of motion artifact,"blurred image" and "stroboscopic image" , have been found in clinical experience, and their theoretical analyzes have been demanded. Assuming that an object is a rigid body, its motion can be divided into rotary and parallel motions. This paper analyzes the degradiation of reconstructed images and artifacts due to the rotary motion of a rigid object. The degradiation of a CT image caused by rotation of an arbitrarily shaped rigid object is formulated by using a point-spread function. The cjaracteristics of blurred images of a rigid object due to its rotation in a CT and the shape of stroboscopic images also are analyzed. The cause of storoboscopic images is explained by using line source. The theories have been confirmed … More by computer simulation.(2) Compton scattering imaging can demonstrate the electron density of a given object which could be important for medical diagnosis. However, clinical application of the technique has not yet been developed, bacause a clear image can not be obtained for several reasons. The image is seriously contaminated by multiple scattering which is inevitable with Compton scattering. The electron density in a small region of the object is not obtained correctly unless multiple scattering is handled carefully. In the present paper, methods to eliminate multiple scattering in Compton scattering imaging system are discussed. A general purpose Monte Carlo code called EGS4 was used to simulate the processes of an incident photon interacting with a substance inside an object. Simulations were performed using a water sphere phantom with a radius of 10 cm irradiated by a beam of monochromatic X-rays at 100 keV.Scattered photons emitted from the phantom were observed and the ratio of the amount of single Compton scattering from a focal point to that of multiple scatterong was calculated. To improve the image quality, elimination of multiple scattering in Compton scattering is indispensable. To this end , theta and phi-collimators and an energy window were proposed and their effects were estimated quantitatively by simulations. It was shown that by introducing of the proposed methods in the imaging system, the ratio of the Compton scattering signal to the multiple scattering noise, S/N,could be improved from 0.022 to 40. Quantitative results derived from the simulations may be useful for the design of a pratical Compton scattering imaging system. Less