基于莫尔条纹螺旋扫描的X射线差分相位衬度层析成像方法

X-ray differential phase-contrast computed tomography (DPC-CT) provides several orders of magnitude higher imaging contrast than the conventional absorption-contrast CT. Moreover, it can be implemented by ordinary incoherent x-ray tube sources and has attracted significant interests. However, due to the use of the phase stepping procedure in which one of the gratings need to be translated step-by-step at each view angle, DPC-CT is currently time-consuming and has an unacceptable imaging dose for clinical applications. Additionally the need for precise translation of the gratings provokes the risk of system instability. So this project proposes to make research on a new DPC-CT method based on helical scanning over moiré fringe. It plans to implement the low-dose, fast and stable phase-contrast tomographic imaging by exploring the phase signal modulation transfer model, the phase signal extraction algorithm, the imaging system and the experimental techniques. The proposed method misaligns the phase grating and the absorption grating to generate the moiré interferogram to modulate the phase signal. Then it adopts the continuous helical motion of the sample to scan the moiré interferogram to extract the phase signal. Due to the removal of the precise translation of the gratings by the use of the continuous helical scanning, the proposed method can reduce the scanning time and the dose and improve the system stability. Furthermore it also has the potential to extend the axial imaging field of view. It would be of significance and helpful to push the development and applications of DPC-CT.

X射线差分相衬层析技术（differential phase-contrast computed tomography, DPC-CT）具有比传统吸收衬度CT高数个量级的对比度，且能利用普通非相干X光管源实现，工程应用潜力巨大。但受光栅步进扫描相位信息提取技术和重建算法制约，其成像时间长、剂量大且不稳定。为此，本项目拟开展基于莫尔条纹螺旋扫描的DPC-CT方法研究，通过对相衬信号调制解调技术、重建算法、成像装置及实验技术的探索，实现低剂量快速稳定的相衬层析成像。该方法偏置光栅形成莫尔条纹调制相位信号，以物体连续螺旋运动代替光栅步进运动对莫尔条纹进行扫描，实现相位信号解调，以融合代数、统计迭代和压缩感知理论的新算法进行图像重建。由于整个扫描过程仅物体做螺旋运动，并降低了对投影数据完备性和噪声要求，该方法能大幅减少扫描时间和剂量，提高稳定性，且能扩大纵向成像视场，对推动相衬CT应用有重要意义。

针对X射线差分相衬层析技术（differential phase contrast computed tomography, DPC-CT）成像时间长、剂量大且不稳定的问题，本项目研究建立了一套快速、低剂量X射线光栅差分相位衬度层析成像方法，探索形成了基于摩尔条纹螺旋扫描和基于错位光栅的差分相衬信号调制解调技术，可在不移动光栅的情况下，实现X射线相位移动信号和强度吸收信号的解析求解，为快速X射线光栅差分相位衬度层析成像奠定了物理学基础；开发形成了基于代数迭代、统计迭代思想及压缩感知理论的低剂量光栅相衬层析重建技术和基于卷积神经网络的不完备投影数据光栅相衬层析重建框架，为低剂量X射线光栅差分相位衬度层析成像提供了算法支持；设计形成了基于摩尔条纹螺旋扫描和错位光栅成像的快速、低剂量X射线光栅差分相位衬度层析成像装置和实验技术；制备了以豚鼠、Nylon、PMMA 及 PTFE 小球为对象的实验样品和人体乳腺组织模体，开展并完成了定性、定量有效性实验研究和应用验证研究，实现了小动物、人体组织模体及材料科学样品的X射线相位衬度层析成像，无损表征了多种样品的X射线吸收和相位衬度特征。由于整个扫描过程仅物体做扫描运动，并降低了对投影数据完备性和噪声要求，该方法能大幅减少扫描时间和剂量，提高稳定性，且能扩大纵向成像视场，对推动相衬CT早日工程应用有重要意义。本项目达到了预期研究目标，获得学术论文、发明专利、特邀报告、人才培养、科技奖励等方面各类成果 39项。