Abstract
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.
Highlights
X-ray nano-tomographic techniques are powerful tools for investigating the fine internal structures of specimens on a nanometer scale[1, 2]
We demonstrated the performance of fast projection-matching algorithm (Faproma) for real projections, which were obtained by a synchrotron transmission X-ray microscope (TXM) at BL01B1 beamline of Taiwan Light Source (TLS)
Based on the comparison of tomography resolution influences, the line profile of the pyrite was obviously narrower and the edge response was sharper in the Faproma than that in IMOD and cross-correlation methods (Fig. 5i), which pointed to better projection registration and subsequent superior reconstruction quality and tomography resolution
Summary
X-ray nano-tomographic techniques are powerful tools for investigating the fine internal structures of specimens on a nanometer scale[1, 2]. In X-ray nano-CT and electron tomography, the most reliable method is still placing nano-particles of high-contrast onto or near the targeted sample as reference points for image alignment. Using this method, projections can be aligned by either manual or automatic particle-tracking methods[5,6,7,8,9]. Parkinson[18] and Yang[21] proposed a method to correct the rotational axis tilt by comparing the tilt difference between two projections obtained from 0° and 180° azimuth angles This correction can roughly improve the accuracy of the initial alignment when using projection matching methods. The convergent process of traditional projection matching methods is still time consuming, and has demanding hardware requirements
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