Parkhurst James M, Thorn Andrea, Vollmar Melanie, Winter Graeme, Waterman David G, Fuentes-Montero Luis, Gildea Richard J, Murshudov Garib N, Evans Gwyndaf
Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, England.
Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, England.
IUCrJ. 2017 Aug 8;4(Pt 5):626-638. doi: 10.1107/S2052252517010259. eCollection 2017 Sep 1.
An algorithm for modelling the background for each Bragg reflection in a series of X-ray diffraction images containing Debye-Scherrer diffraction from ice in the sample is presented. The method involves the use of a global background model which is generated from the complete X-ray diffraction data set. Fitting of this model to the background pixels is then performed for each reflection independently. The algorithm uses a static background model that does not vary over the course of the scan. The greatest improvement can be expected for data where ice rings are present throughout the data set and the local background shape at the size of a spot on the detector does not exhibit large time-dependent variation. However, the algorithm has been applied to data sets whose background showed large pixel variations (variance/mean > 2) and has been shown to improve the results of processing for these data sets. It is shown that the use of a simple flat-background model as in traditional integration programs causes systematic bias in the background determination at ice-ring resolutions, resulting in an overestimation of reflection intensities at the peaks of the ice rings and an underestimation of reflection intensities either side of the ice ring. The new global background-model algorithm presented here corrects for this bias, resulting in a noticeable improvement in factors following refinement.
本文提出了一种算法，用于对一系列包含样品中冰的德拜-谢乐衍射的X射线衍射图像中每个布拉格反射的背景进行建模。该方法涉及使用从完整的X射线衍射数据集生成的全局背景模型。然后针对每个反射独立地将该模型拟合到背景像素。该算法使用在扫描过程中不变的静态背景模型。对于整个数据集中都存在冰环且探测器上一个斑点大小的局部背景形状不表现出较大时间依赖性变化的数据，有望获得最大的改进。然而，该算法已应用于背景显示出较大像素变化（方差/均值>2）的数据集，并已证明可改善这些数据集的处理结果。结果表明，在传统积分程序中使用简单的平背景模型会在冰环分辨率下的背景确定中导致系统偏差，从而导致冰环峰值处的反射强度被高估，而冰环两侧的反射强度被低估。本文提出的新的全局背景模型算法校正了这种偏差，从而在精修后的因子方面有显著改善。
