Studies of signal estimation bias in grating-based x-ray multicontrast imaging.
Studies of signal estimation bias in grating-based x-ray multicontrast imaging.
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DOI：
10.1002/mp.12235
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发表时间：
2017-06
期刊：
影响因子：
3.8
通讯作者：
Chen GH
中科院分区：
文献类型：
--
作者：
Ji X;Ge Y;Zhang R;Li K;Chen GH
在基于光栅的 X 射线多对比成像中，可以根据同一组采集的数据来估计三种对比机制（吸收对比、微分相位对比 (DPC) 和暗场对比）的信号。估计信号 N0（与吸收相关）、N1（与暗场相关）和 φ（与 DPC 相关）可能存在固有偏差。然而，目前尚不清楚这些偏差有多大以及数据采集参数如何影响提取信号中的偏差。本文的目的就是解决这些问题。针对众所周知的信号估计方法，对提取信号的偏差（即 N0、N1 和 φ）进行了理论上的研究。从带有光子计数探测器的基于光栅的 X 射线多对比台式成像系统获取的实验数据用于验证三种对比机制的信号偏差的理论结果。理论和实验研究均表明：（1）吸收对比信号的信号估计偏差为零； (2) N1的信号估计偏差与相位步数和光栅干涉仪的平均条纹可见度成反比，但偏差与信号电平之比（即相对偏差）与相位步数无关； (3) 信号估计的偏差取决于平均 DPC 信号水平、多对比数据采集的总曝光水平以及干涉仪的平均条纹可见度。在基于光栅的X射线多重对比成像中，估计的吸收对比信号是无偏的；估计的暗场对比度信号有偏差，但相对偏差仅取决于干涉仪的平均条纹可见度和曝光水平。估计的 DPC 信号可能有偏差，偏差水平取决于平均信号水平、曝光水平和干涉仪性能。
In grating-based x-ray multi-contrast imaging, signals of three contrast mechanisms-absorption contrast, differential phase contrast (DPC), and dark-field contrast-can be estimated from the same set of acquired data. The estimated signals, N0 (related to absorption), N1 (related to dark-field), and φ (related to DPC) may be intrinsically biased. However, it is yet unclear how large these biases are and how the data acquisition parameters affect the biases in the extracted signals. The purpose of this paper was to address these questions. The biases of the extracted signals (i.e., N0, N1 and φ) were theoretically studied for a well-known signal estimation method. Experimental data acquired from a grating-based x-ray multi-contrast benchtop imaging system with a photon counting detector were used to validate the theoretical results for the signal biases of the three contrast mechanisms. Both theoretical and experimental studies showed the following results: (1) The bias of signal estimation for the absorption contrast signal is zero; (2) The bias of signal estimation for N1 is inversely proportional to the number of phase steps and to the average fringe visibility of the grating interferometer, but the ratio between the bias and the signal level (i.e., the relative bias) is independent of the number of phase steps; (3) The bias of signal estimation for φ depends on the mean DPC signal level, the total exposure level of the multi-contrast data acquisition, and the mean fringe visibility of the interferometer. In grating-based x-ray multi-contrast imaging, the estimated absorption contrast signal is unbiased; the estimated dark-field contrast signal is biased, but the relative bias is only dependent on the mean fringe visibility of the interferometer and the exposure level. The estimated DPC signal may be biased, and the bias level depends on the mean signal level, the exposure level, and the interferometer performance.
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