生物样品的大视场连续太赫兹波叠层成像方法研究

Terahertz (THz) radiation, due to its unique propagation features such as non-ironization, high-penetration and water-absorption, has been widely used for biomedical imaging. Ptychography is a lensless imaging technique that aims to reconstruct an object from a set of coherent diffraction patterns originating from different and partially overlapping sample illumination areas. In this proposal, ptychography is firstly applied in THz domain. A high-resolution whole-field imaging method is proposed for biomedical samples based on continuous-wave (CW) THz ptychography. .Firstly, based on the transmission and coherent characteristics of CW THz radiation, we would investigate the imaging mechanism of the terahertz ptychography with the exact diffraction propagation theory, and quantitatively assess the inherent relationship of the spatial resolution, field of view, depth of focus and depth of field, which are key issues for evaluating the imaging system. Correspondingly, the optimization of the imaging system is carried out considering the measurement conditions of biological samples. Secondly, based on Gaussian fitting, high quality terahertz diffraction patterns would be obtained. Also, lensless Fourier digital holographic guided ptychography is proposed as a real-time visible feedback during the experiment to identify the illuminated area. The extrapolation phase retrieval algorithm would be developed to exceed the numerical aperture of the detector and enhance the resolution. The high-resolution, high-fidelity quantitative distribution of the amplitude and phase information would be therefore obtained from the THz ptychograms. The experimental setup will be built based on CW THz laser and pyroelectric array camera, and applied for the practical biomedical imaging such as nanoparticle-enabled target drug distribution observation. With the prospective results, we would establish the relationships between THz complex amplitude distribution (both amplitude and phase contrast images) and physiological parameters of biological samples, which are very useful for the biomedical science. .The project will and shall provide a high-resolution non-destructive quantitative CW THz imaging method for visualized biomedical research.

太赫兹波具有独特的低能性、高穿透性、惧水性等成像特性，在生物医学领域具有重要的应用。叠层成像是一种从交叠采集的冗余衍射图样中恢复出样品复振幅信息的先进成像技术。本项目首次将叠层成像引入太赫兹波段，提出大视场高分辨率、无损快速获取定量振幅和相位信息的连续太赫兹波叠层成像技术。.首先，基于太赫兹波的传输理论和相干特性，研究连续太赫兹波叠层成像机理，分析成像空间分辨率、视场、焦深与景深的内在制约关系，结合实际样品实验条件，优化系统设计。其次，研究基于高斯拟合的图像叠加方法提高衍射图像信噪比，引入无透镜傅里叶变换数字全息实现扫描区域动态可视观测，发展相位复原的迭代算法突破探测器数值孔径。最后，构建实际生物样品的成像装置，并开展纳米造影靶药追踪等生物成像观测研究，建立起太赫兹波振幅和相衬图像信息与样品生理学参数的联系。.本项目的开展将为现代生物医学的无损可视化研究提供一种极具潜力的太赫兹成像技术。

本项目旨在太赫兹波段发展新型相衬成像和三维层析成像技术并开展应用探索研究。发表SCI论文16篇，授权发明专利7项。在叠层成像方面，提出了基于物面交叠区域复振幅求互相关的叠层探针位置校正方法，提高了成像质量；提出了基于发散球面波照明的叠层外推再现算法，提高了成像分辨率；提出了基于双物面记录的叠层采样方式，提高了再现算法的收敛性和计算速率。面向透射式、反射式、多物面等不同类型的样品，提出了并构建了多种连续太赫兹波叠层成像光路，拓展了基于前向散射模型的3D-PIE再现算法，提出基于频域坐标变换的倾斜光照明衍射图畸变校正方法，获得了西门子星、蝉翅、文竹等样品的幅值和相位图像。并将叠层成像的算法扩展到一般的波前光场的拼接应用中，提出了一种高保真的复振幅波前拼接方法。先后将共光路数字全息、强度传输方程算法、无透镜傅里叶变换数字全息、全内反射数字全息引入到太赫兹波段，发展出了多种连续太赫兹波全场相衬成像方法，提出了基于反射式连续太赫兹波数字全息的隐藏物体形貌检测方法，基于亚像素级配准和图像融合扩大成像视场；提出基于菲涅耳反射镜的太赫兹自参考数字全息成像方法，获得了分辨率板、压纹聚丙烯板、蝉翅的再现结果；基于衰减全内反射棱镜实现太赫兹波段的折射率二维全场测量，实现了酒精水溶液挥发过程中折射率变化的动态定量观测；提出太赫兹无透镜傅里叶变换数字全息，获得了西门子星和压纹聚丙烯板的再现结果，实时全场监测水生植物叶片含水量变化。开展连续太赫兹波三维层析成像方法研究，基于锥镜产生贝塞尔光束扩大成像景深，并将太赫兹计算层析应用于鸡尺骨不同位置剖面的骨密度测量。提出连续太赫兹波衍射层析成像方法，获得了高精度的聚丙乙烯小球三维折射率分布。综上，通过本项目的开展，发展出了多种连续太赫兹波无透镜全场相衬成像和计算层析成像技术，在生物成像、材料表征、无损检测等领域具有重要的应用潜力。