针对医用X线CT成像系统的多色能谱X线在成像过程中出现的CT图像硬化伪影,会降低图像质量,干扰诊断等问题,需要对CT硬化伪影进行校正.本文对于单介质水和水骨混合物分别提出了一种基于投影空间优化的多项式拟合校正方法.首先,构建投影校正模型和理想投影模型;然后,将构建的投影校正模型与理想投影模型做对比,差异最小时确定校正系数;最后,把校正系数代入投影校正模型中再重建图像.经仿真实验结果表明,所提出的多项式拟合校正方法能够很好地去除CT硬化伪影,提高图像精度,对CT的精准定量分析具有重大意义.
X ray spectrum of medical CT imaging system is polychromatic, which will cause CT image hardening artifacts, reduce image quality and interfere diagnosis.Therefore,the correction of the hardening artifacts of CT images is necessary. In this paper, a polynomial fitting correction method is proposed based on projection space optimization for single medium water and water bone mixture. Firstly, the projection correction model and the ideal projection model are constructed. Then, the projection correction model is compared with the ideal projection model to determine the correction coefficient when the difference is minimum. Finally, the correction coefficient is substituted into the projection correction model,and the corrected image can be reconstructed. The simulation results show that the proposed polynomial fitting correction method can remove CT hardening artifacts and improve the image accuracy, which is of great significance in the accurate quantitative analysis of CT.
[1] 黄魁东,张定华,孔永茂,等. 基于切片轮廓重投影的锥束CT射束硬化校正方法[J]. 仪器仪表报,2008(9):1873-1877. DOI:10.19650/j.cnki.cjsi.2008.09.016. HUANG K D,ZHANG D H,KONG Y M, et al. Beam hardening correction method for Cone-Beam computed tomography based on reprojection of slice contours[J]. Chinese Journal of Seientific Instrument, 2008(9):1873-1877. DOI:10.19650/j.cnki.cjsi.2008.09.016.
[2] 曾刚, 郁忠强, 阎永廉.基于蒙特卡罗模拟的射束硬化校正方法[J].高能物理与核物理,2006,30(2): 178-182.DOI:10.3321/j.issn:0254-3052. ZENG G, YU Z Q, YAN Y L. Beam hardening correction based on Monte Carlo simulation[J]. High Energy Physics And Nuclear Physics, 2006, 30(2): 178-182. DOI:10.3321/j.issn:0254-3052.
[3] 张全红,路宏年,杨民. 基于重投影的多项式拟合校正射束硬化[J]. 光学技术,2005(4):633-635. DOI:10.13741/j.cnki.11-1879/o4.2005.04.050. ZHANG Q H,LU H N,YANG M. Beam hardening correction using polynomial fitting based on reprojection[J]. Optical Technique,2005(4):633-635. DOI:10.13741/j.cnki.11-1879/o4.2005.04.050.
[4] 张俊,李磊,张峰,等. X射线CT 射束硬化校正方法综述[J].CT理论与应用研究,2013,22(1): 195-204.DOI:1004-4140(2013)01-0195-10. ZHANG J, LI L, ZHANG F, et al. Review of the methods for beam hardening correction in X-ray computed tomography[J].CT Theory and Applications, 2013, 22(1): 195-204. DOI: 1004-4140(2013)01-0195-10.
[5] HERMAN G T. Correction for beam hardening in computed tomography[J]. Physics in Medicine and Biology, 1979, 24(1): 81-106.DOI: 10.1088/0031-9155/24/1/008.
[6] COLEMAN A J,SINCLAIR M. A beam-hardening correction using dual-energy computed tomography[J]. Physics in Medicine and Biology, 1985, 30(11):1251-1256. DOI: 10.1088/0031-9155/30/11/007.
[7] ELBAKRI I A, FESSLER J A. Statistical reconstruction algorithms for polyenergetic X-ray computed tomography[J]. IEEE Transactions on Medical Imaging, 2002, 21(2): 89-99. DOI: 10.1109/42.993128.
[8] NALCIOGLU O,LOU RY. Post-reconstruction method for beam hardening in computerised tomography[J]. Physics in Medicine and Biology, 1979, 24(2):330-340. DOI: 10.1088/0031-9155/24/2/009.
[9] 连亚琴. CT射束硬化校正算法研究[D].太原:中北大学,2009. LIAN Y Q. The algorithms study of beam-hardening correction[D]. Taiyuan: Northwest University, 2009.
[10] 张学松, 赵柏山. 基于Radon变换的CT图像杯状伪影校正[J].CT理论与应用研究,2016,25(5): 539-546. DOI:10.15953/j.1004-4140.2016.25.05.05. ZHANG X S, ZHAO B S. Cupping artifacts calibration in CT image based on radon transform[J]. CT Theory and Applications, 2016, 25(5): 539-546. DOI:10.15953/j.1004-4140. 2016.25.05.05.
[11] 张益海,张催,潘小东,等.锥束工业CT射束硬化校正方法[J].无损检测,2017,39(6):8-12. DOI:10.11973/wsjc201706002. ZHANG Y H, ZHANG C, PAN X D, et al. Hardening correction method of cone beam industrial CT[J]. Non-Destructive Testing, 2017, 39(6):8-12. DOI:10.11973/wsjc201706002.
[12] KYRIAKOU Y, MEYER E, PRELL D, et al. Empirical beam hardening correction(EBHC)for CT[J]. Medical Physics, 2010, 37(10): 5179-5187.DOI: 10.1118/1.3477088.
