National Synchrotron Radiation Research Center, 30076, Hsinchu, Taiwan.
Department of Earth Sciences, National Cheng Kung University, 70101, Tainan, Taiwan.
Sci Rep. 2017 Jun 16;7(1):3691. doi: 10.1038/s41598-017-04020-0.
X-ray 3D tomographic techniques are powerful tools for investigating the morphology and internal structures of specimens. A common strategy for obtaining 3D tomography is to capture a series of 2D projections from different X-ray illumination angles of specimens mounted on a finely calibrated rotational stage. However, the reconstruction quality of 3D tomography relies on the precision and stability of the rotational stage, i.e. the accurate alignment of the 2D projections in the correct three-dimensional positions. This is a crucial problem for nano-tomographic techniques due to the non-negligible mechanical imperfection of the rotational stages at the nanometer level which significantly degrades the spatial resolution of reconstructed 3-D tomography. Even when using an X-ray micro-CT with a highly stabilized rotational stage, thermal effects caused by the CT system are not negligible and may cause sample drift. Here, we propose a markerless image auto-alignment algorithm based on an iterative method. This algorithm reduces the traditional projection matching method into two simplified matching problems and it is much faster and more reliable than traditional methods. This algorithm can greatly decrease hardware requirements for both nano-tomography and data processing and can be easily applied to other tomographic techniques, such as X-ray micro-CT and electron tomography.
X 射线三维层析技术是研究标本形态和内部结构的有力工具。获取三维层析的一种常见策略是，将样本安装在精细校准的旋转台上，从不同的 X 射线照明角度捕获一系列 2D 投影。然而，三维层析的重建质量依赖于旋转台的精度和稳定性，即 2D 投影在正确的三维位置上的精确对准。对于纳米层析技术来说，这是一个关键问题，因为在纳米级水平上，旋转台的机械不完美是不可忽略的，这会显著降低重建的 3D 层析的空间分辨率。即使使用具有高度稳定旋转台的 X 射线微 CT，CT 系统引起的热效应也不可忽略，并且可能导致样本漂移。在这里，我们提出了一种基于迭代方法的无标记图像自动对准算法。该算法将传统的投影匹配方法简化为两个简化的匹配问题，它比传统方法快得多，也可靠得多。该算法可以大大降低纳米层析术和数据处理的硬件要求，并且可以很容易地应用于其他层析技术，如 X 射线微 CT 和电子层析术。
