Study On Measurement Of X-ray Spectra And Beam Hardening Correction For Industrial CT

Industrial computed tomography(ICT)is one of the nondestructive testing method which is based on the scan of the workpiece tomography to obtain the projection data.Through the digital image processing can obtain CT image.According to the gray level image which can detect the object's tomography.So we can ascertain the internal defect and density and composition of materials of the object.At present,industrial computed tomography as the best nondestructive testing method in the field of industry,which is not affected by the shape and material of the object.Since the X-ray beam is composed of different energy photons in the cone beam X-ray computed tomography imaging system.The low energy photons decay more than the high energy photons in the transmission process.This leads to the X-ray hardening effect.This effect will lead to the original uniform density of the measured objects which performance different brightness and the gray value is not equal in reconstruction of CT image,so as to make the reconstruction image in the goblet artifact and strip artifact.It is necessary to study methods of the hardening correction in order to reduce the effects of hardening effect.The method of polynomial fitting hardening correction is commonly used calibration method in CT system.The ray transmission intensity that through different thickness sample which is the same material as absorbent sheet can be obtained by experiment.The relationship between transmission thickness and pluripotent projection can be obtained and then taking the tangent at the origin of the curve as the relationship between curve of the equivalent single energy projection and the transmission thickness.Finally,using polynomial fitting can obtain relationship between pluripotent projection and equivalent single projection,so as to realize hardening correction.The method has a main disadvantage is that it is according to the requirement which is necessary to prepare absorbent filter.However,the thickness of the absorbing filter is difficult to be made small enough,leading to the tangent at the origin is not accurate enough.And it is difficult to find the same samples absorbent filter which is composed of a variety of materials.The method of Monte Carlo simulate can obtain the corresponding result that the experiment of ray transmission the absorption material.Compared with the traditional experimental measurements,the advantage is that the thickness and material can be easily defined,and a large amount of experimental measurement time can be reduced.However,the method of Monte Carlo simulation often make the result in a large error which is due to the lack of the initial energy spectrum of the X ray tube.In this paper that provides the basis for the beam hardening correction.A method of beam hardening correction is put forward,which is based on the experimental spectrum and Monte Carlo simulation of polynomial fitting.Based on the initial X-ray energy spectrum by experiment measuring.The relationship between transmission thickness and pluripotent projection can be obtained by exploiting Monte Carlo simulation and then using polynomial fitting can obtain relationship between pluripotent projection and equivalent single projection,so as to realize hardening correction.Respectively use this method and the traditional filter method for X-ray hardening correction on some aluminum workpieces.The experimental results show that after using two methods of hardening correction can improve image quality in reconstruction of CT image but the proposed method is better than the filter method which can decrease cone-beam CT beam hardening artifacts effectively.It provides an effective correction method for cone beam industrial computed tomography beam hardening correction.