| Computed Tomography Technique is one of the most advanced non-destructive detection techniques at present. The images reconstructed by CT are of good quality and high resolution. Furthermore, CT images can be processed and analyzed digitally. So CT is widely applied in aviation, astronautics, mechanics, shipping, public security, customs, medicine, and many other areas. CT technique is mostly composed of two sections: the software and the hardware, and the core of the former is the image reconstruction algorithm.Beam-hardening correction is of importance in CT reconstruction algorithm. Classical reconstruction algorithms assume that the X-ray is monochromatic while in fact X-ray is polychromatic either in industrial or in medical CT, so only polychromatic projection data have been obtained in actual CT system. Once this kind of data is used to reconstruct the image directly, beam-hardening artifacts appear in the reconstructed image. In order to eliminate the beam-hardening artifacts, most current correction algorithms have to assume that the X-ray beam spectra are known and themass attenuation coefficients of the detected object related to different energy are given. However, the beam spectrum of a CT system is not constant normally.Firstly, an estimation algorithm for spectrum of the CT system is presented in the paper by using a standard cylinder or wedge phantom, where the mass attenuation coefficient of the contained material of the phantom is not necessarily to be known. Especially, the algorithm obtains the phantom's mass attenuation coefficient and spectrum of the CT system at the same time.Secondly, a beam-hardening correction algorithm for single material object is given in the paper, which is more precise than polynomial approaching correction algorithm and more rapid than common iterative algorithm. Also, a beam-hardening correction research on the double-material object is given. And the numerical experiment results show that the beam-hardening artifacts can be eliminated in the reconstructed image using the latter algorithm, furthermore, it can be applied to multi-material object. |
