工业CT在工件检测中X射线硬化校正

X射线工业CT中，由于X射线能谱具有多色性，X射线在透射物质时，能量较低的射线优先被吸收，X射线能量越高，衰减系数越低。也即较高能量的X射线的衰减系数比较低能量的X射线的衰减系数小。射线随透射厚度增大，变得更易穿透，也就是发生了能谱硬化现象。由于射线硬化现象使图像重建时出现伪影，因此必须修正。文中对X射线硬化现象进行了分析，探讨了在均匀物质中，X射线射束和与透射厚度的关系。并根据Beer定律和X射线与物质作用的特点，通过获取X射线射束和数据，拟合出射束和与透射厚度的关系式。然后得出在同一透射厚度时，X射线射束和校正为单色等效射束和的关系及其等效方法。最终得出X射线等效单色射线的衰减系数的拟合值。再对此衰减系数拟合值进行卷积反投影重构，即可有效消除X射线射束硬化的影响。

X-Ray Hardening Correction for ICT in Testing Workpiece

Since energy spectrum of X-ray is polychromatic source in X-ray industrial computerized tomography,the variation of attenuation coefficient with energy leads to the lower energy of X-ray radiation being absorbed preferentially when X-ray is transmitting the materials.And the higher the energy of X-ray,the lower the attenuation coefficient of X-ray.With the increase in the X-ray transmission thickness,it becomes easier for the X-ray to transmit the matter.Thus, the phenomenon of energy spectrum hardening of X-ray takes place,resulting from the interaction between X-ray and the materials.This results in false images in the reconstruction of X-ray industrial computerized tomography.Therefore,hardening correction of energy spectrum of X-ray has to be done.In the present paper,not only is the hardening phenomenon of X-ray transmitting the materials analyzed,but also the relation between the X-ray beam sum and the transmission thickness of X-ray is discussed.And according to the Beer law and the characteristics of interaction when X-ray is transmitting material,and by getting the data of X-ray beam sum,the relation equation is fitted between the X-ray beam sum and X-ray transmission thickness.Then,the relation and the method of equivalence are carried out for X-ray beam sum being corrected.Finally,the equivalent and monochromatic attenuation coefficient fitted value for X-ray transmitting the material is reasoned out.The attenuation coefficient fitted value is used for product back-projection image reconstruction in X-ray industrial computerized tomography.Thus,the effect caused by X-ray beam hardening is wiped off effectively in X-ray industrial computerized tomography.