三维X射线显微技术与小型-微体化石高分辨率无损成像

HIGH-RESOLUTION TOMOGRAPHY OF MILLIMETER-TO CENTIMETER-SIZED FOSSILS USING THREE-DIMENSIONAL X-RAY MICROSCOPY

在古生物学研究中,以X射线断层成像(Computed Tomography)为代表的三维无损成像技术可以在不破坏化石标本的前提下,同时获得标本外观形态和内部结构的信息,相比传统的可见光成像手段有着明显优势。为推动化石三维无损成像技术在国内古生物学领域的发展,本文系统介绍一种新型显微CT技术——三维X射线显微术(Three-Dimensional X-ray Microscopy)。与基于几何放大和吸收衬度成像的传统显微CT技术相比,该技术有若干优势:(1)将同步辐射X射线显微断层成像的光学成像系统引入基于实验室X射线源的显微CT系统中,在几何放大的基础上增加了光学放大,优化了传统显微CT的系统架构,弥补了传统显微CT单纯依靠几何放大的不足,提高了空间分辨率;(2)采用可移动的X射线源和优化的光学成像系统,实现了低能X射线相位衬度成像,可以三维重构传统显微CT技术无法有效探测的、低吸收衬度的化石标本;(3)基于新的成像架构和成像算法,实现了厘米-分米级较大标本内部"感兴趣区域"(Region of Interest)精确导航和局部高分辨率(微米-亚微米空间分辨)成像;(4)可以实现小型扁平标本(宽厚比>4,宽<10cm)高效率、高分辨率成像和长条形微体标本长轴方向自动分段无缝拼接的微米至亚微米级高分辨率重建,弥补了传统工业显微CT针对小型扁平标本和长条形微体标本高分辨成像效果不佳的缺陷。这些优势使得基于实验室X射线源的显微CT成像技术可以获得接近同步辐射X射线源的成像质量,从而有效推动化石生物学研究。

Among imaging techniques for paleontology, computed tomography （CT） is an unparallel one when comparing to conventional optical and electronic imaging methods, because it can reconstruct both external and internal structures of fossils without destroying them. As a powerful non-destructive three-dimensional imaging technique, CT is widely used in paleontological community recent years. Here, we introduce a new micro-CT technique, three-dimensional X-ray microscopy （ 3D-XRM ）. Different from the conventional miero-CT characterized by geometric magnification and absorption contrast, this new technique has four merits. （1） it can provide micron to sub-micron spatial resolution due to a CCD-based optical system~ （2） it can reconstruct centimeter-to millimeter-sized specimens with low- Z materials using propagation phase contrast imaging mode~ （3） based on the new architecture and specific algorithms, the system has a ＂zoom-in function＂ which can precisely reconstruct any ＂region of interests （ROIs）＂ located inside a comparatively large specimen with micron to sub- micron resolution; （4） contrary to conventional micro-CT, this new system can reconstruct small size high aspect-ratio flat specimens （width 10 cm） and tubular microfossils with high resolution. Owing to the merits, 3D-XRM can provide high quality reconstructions for millimeter- to centimeter-sized fossils with three-dimensional preservation.