Department of Imaging Science and Technology, Delft University of Technology, Delft, The Netherlands.
Med Phys. 2011 Sep;38(9):5136-45. doi: 10.1118/1.3622606.
The implementation of in-line x-ray phase contrast imaging (PCI) for soft-tissue patient imaging is hampered by the lack of a bright and spatially coherent x-ray source that fits into the hospital environment. This article provides a quantitative characterization of the phase-contrast enhancement of a PCI system based on the miniature synchrotron technology MIRRORCLE-6X.
The phase-contrast effect was measured using an edge response of a plexiglass plate as a function of the incident angle of radiation. We have developed a comprehensive x-ray propagation model based on the system's components, properties, and geometry in order to interpret the measurement data. Monte-Carlo simulations are used to estimate the system's spectral properties and resolution.
The measured ratio of the detected phase-contrast to the absorption contrast is currently in the range 100% to 200%. Experiments show that with the current implementation of the MIRRORCLE-6X, a target smaller than 30-40 μm does not lead to a larger phase-contrast. The reason for this is that the fraction of x-rays produced by the material (carbon filament and glue) that is used for mounting the target in the electron beam is more than 25% of the total amount of x-rays produced. This increases the apparent source size. The measured phase-contrast is at maximum two times larger than the absorption contrast with the current set-up.
Calculations based on our model of the present imaging system predict that the phase-contrast can be up to an order of magnitude larger than the absorption contrast in case the materials used for mounting the target in the electron beam do not (or hardly) produce x-rays. The methods described in this paper provide vital feedback for guiding future modifications to the design of the x-ray target of MIRRORCLE-type system and configuration of the in-line PCI systems in general.
由于缺乏适合医院环境的明亮、空间相干的 X 射线源，因此，将线内 X 射线相衬成像（PCI）技术应用于软组织患者成像受到阻碍。本文对基于微型同步加速器技术 MIRRORCLE-6X 的 PCI 系统的相衬增强作用进行了定量描述。
采用有机玻璃板边缘响应作为辐射入射角的函数，测量了相衬增强效果。我们根据系统的组件、特性和几何形状，开发了一个全面的 X 射线传播模型，以便解释测量数据。蒙特卡罗模拟用于估计系统的光谱特性和分辨率。
目前，测量得到的检测到的相衬与吸收衬度之比在 100%到 200%之间。实验表明，在当前 MIRRORCLE-6X 的实现下，目标小于 30-40μm 不会导致更大的相衬增强。其原因在于，用于将目标安装在电子束中的材料（碳纤维灯丝和胶水）所产生的 X 射线比例超过了总 X 射线量的 25%。这增加了表观源尺寸。目前的设置下，测量得到的相衬最大比吸收衬度大两倍。
基于对当前成像系统的模型计算表明，在用于将目标安装在电子束中的材料不（或几乎不）产生 X 射线的情况下，相衬可以比吸收衬度大一个数量级。本文描述的方法为指导未来对 MIRRORCLE 型系统的 X 射线目标和线内 PCI 系统的配置的设计改进提供了重要反馈。
