在锥束计算机断层扫描(CT)系统中,由于不易放置后准直器,未经校正的散射信号会导致测量信号偏离真实值,降低图像的对比度和信噪比,甚至产生伪影。利用散射校正板(BSA)可以有效估计射线穿过工件后的散射信号分布。将BSA散射校正方法应用于锥束微纳CT系统,通过在X射线源与工件之间放置校正板的方式获取散射分布。首先介绍了基于BSA散射校正的基本原理,给出了具体的实验装置和实验步骤,然后使用自主研制的锥束微纳CT系统对几种工件进行扫描成像,最后从DR投影、重建切片、三维重建图像等多个角度对图像质量进行分析。结果表明,基于BSA的散射校正方法能够有效减少锥束微纳CT系统的散射伪影,改善图像质量,验证了BSA方法应用于锥束微纳CT系统的可行性。考虑微纳CT射线源能量低、焦点漂移影响大等因素,可在散射校正的基础上增加硬化校正和焦点漂移校正,进一步对图像进行修正。

In cone-beam computed tomography (CT) systems, due to the difficult placing of the rear collimator, uncorrected scatter signals can cause a deviation of the measured values from the true ones, reducing the image contrast and signal-to-noise ratio and even producing artifacts. However, a beam stop array (BSA) can be used to effectively estimate the scatter signal distribution after the beam passing through the sample. In this study, the BSA correction method is applied for a cone-beam micro-CT system; the scatter distribution is obtained by placing a correction plate between the X-ray source and the sample. First, the basic principle of BSA-based scatter correction is introduced and the specific experimental devices and steps are given. Then, several samples are analyzed with an independently developed cone-beam micro-CT system. Finally, the quality of the obtained images is evaluated based on digital radiography projections, reconstruction slices, three-dimensional reconstruction images, and so on. Results show that the BSA correction method can effectively reduce the scatter artifacts in cone-beam micro-CT systems and improve the image quality, which verifies the feasibility of applying BSA correction method to cone-beam micro-CT systems. Given the low energy of the X-ray source and the large influence of the focus drift, beam-hardening correction and focus-drift correction are also included, further improving the image quality.