The Algorithms Study Of Beam-hardening Correction

Computed Tomography Technique which has been widely used in many ways is one of the most advanced non-destructive detection techniques at present. It is especially used in industry inspection and medical diagnosis because the image reconstructed by CT are of good quality and high resolution.Traditional 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. It is one dimension to improve the image quality by correcting beam-hardening.Firstly, an improved algorithm of CT image hardening correction based on original projection is presented in the paper. As to the characteristic of noise in the high frequency mostly, we divide the projection into high and low frequency. And moreover, we adopt the improved method this paper researched to the low frequency. Then, the result is added to the high frequency and image is reconstructed by filtered backprojection method. A prior CT scan and complex operations were not necessary for this correction method. So it is much simpler and quicker, with better signal-noise-ratio, and not affected by scan conditions.Secondly, a method for estimating the X-ray spectrum is presented and a beam-hardening correction algorithm is given based on this in the paper. First, image is reconstructed by the gained projection and information about the object is collected; next, we could get correlation between monochromatic and polychromatic projection which are discrete; then, we make correction with this relation. The experiment shows that the beam-hardening artifacts were eliminated effectively and this method is applicable to a large number of object detections.Last, in this paper, beam hardening artifacts are diminished or removed by the combination method of software and hardware. Through prepositioned filter whose material is the same as one of the target on CT, the average energy of X-ray was increased. At the same time, the method of reprojection is used to correct the beam hardening. Research shows this method can eliminate beam hardening affect effectively.