Grating-based X-ray Phase-contrast Tomography Methods

描述（申请人提供）：生物软组织主要由轻元素组成，其组成几乎均匀，密度变化很小。传统的基于衰减的x射线成像不能为这类材料提供足够的对比度。在诊断能量范围内，软组织x射线相移的横截面比x射线衰减的横截面大3个数量级。因此，x射线相衬成像对细微特征，特别是软组织的微观结构非常敏感，为各种正常和病变情况的分析提供了优越的对比。x射线相衬成像方法在生物医学应用中面临挑战。基于分析仪的相衬成像需要单色x射线和高精度晶体，但仅限于同步辐射设备。基于传播的成像受到微聚焦x射线管光子通量低的影响。基于光栅的相衬成像是最近的一项突破。然而，这种模式转变的两个主要障碍是：(1)小周期和高方面的大面积光栅；(2)数据采集所需的时间长。从技术上讲，制作大型光栅是相当困难的，特别是当x射线能量很高时。从理论上讲，模拟x射线从点x射线源通过大光栅的传播是非常复杂的。在这个项目中，我们将建立两个启用创新，它们是(1)内部阶段

DESCRIPTION (provided by applicant): Biological soft tissue consists mainly of light elements, and its composition is nearly uniform with little density variation. Traditional attenuation-based x-ray imaging cannot provide sufficient contrast for this type of materials. The cross-section of x-ray phase shift is three orders of magnitude greater than that of x-ray attenuation in soft tissue over the diagnostic energy range. Hence, x-ray phase-contrast imaging is sensitive to subtle features especially micro-structures of soft tissue and offers superior contrast for analyses of various normal and diseased conditions. X-ray phase-contrast imaging approaches face challenges in biomedical applications. Analyzer-based phase- contrast imaging requires monochromatic x-rays and high-precision crystals, being limited to the synchrotron radiation facility. Propagation-based imaging suffers from a low photon flux of a micro-focus x-ray tube. Grating-based phase-contrast imaging is a recent breakthrough. However, two main obstacles for this paradigm shift are (1) the large-area gratings of small periods and high aspects and (2) the long time needed for data acquisition. Technically, it is rather difficult to make large gratings especially when x-ray energy is high. Theoretically, it is extremely complicated to model the propagation of x-rays through large gratings from a point x-ray source. In this project, we will establish two enabling innovations that are (1) interior phase contrast tomography for accurate region of interest (ROI) reconstruction and (2) few-view phase-contrast reconstruction without phase-stepping for accelerated data acquisition and minimized radiation dose. The synergistic combination of these innovations will define a new frontier of x-ray phase-contrast tomography. Although the conventional wisdom is that grating-based phase-contrast tomography must use sufficiently large gratings to cover an object and capture projections completely, our main innovative thinking is to target theoretically exact reconstruction over an ROI from truncated data collected with relatively small gratings. It is underlined that the grating-based phase-contrast interior reconstruction takes truncated differential projections, while the typical interior reconstruction assumes truncated direct projections. Another new idea for this project is to utilize the reweighted L1 norm for fewer-view image reconstruction. The overall goal of this project is to establish x-ray-grating-based interior tomography theory, develop the associated few-view reconstruction methods and system without phase stepping, and promote its biomedical applications. The proposed technology will be characterized in numerical simulation and phantom experiments, and applied for musculoskeletal imaging in an animal model. Upon the completion of this project, the proposed grating-based system will have achieved 30¿m resolution, shortened scanning time, and reduced radiation dose over a 3cm- diameter ROI, outperforming micro-CT in terms of contrast resolution yet delivering comparable ROI image quality relative to that of conventional grating-based phase-contrast tomography.