论文部分内容阅读
In X-ray computed tomography(CT),beam hardening artifact is caused by polychromatic energy spectrum and energy dependency attenuation coefficient,which not only affects the quality of the image but also reduces the identification ability of the image and the precision of CT Value measurement.There is a simple and effective method for the beam hardening artifact correction to attenuate preferentially lower energy X-rays with a filter.However,a large amount of experiments are often requires for the method to select the filter material and thickness while lacking of quantitative analyses and selection criteria.In this work,a novel filter-based beam hardening artifact correction method is presented.Firstly,the spectrum of X-ray source under current tube voltage is estimated by means of the regular optimization method via the transmission data of a QRM water phantom.According to our proposed attenuation coefficient curve change rate of the object material as a function of energy,the energy range to be filtered can be quantitatively determined.The Monte Carlo method is used in combination to simulate the spectrum filtering performance using different filter materials and thicknesses.Based on the proposed high-low energy integral ratio of transmission photons,the optimized filter material and thickness are determined to attenuate low energy photons at utmost and preserve as many high energy photons as possible,which is of great significance in improving the signal to noise ratio(SNR)of the corrected CT image.The effectiveness of the proposed method is demonstrated in both simulation and experimental results on a head phantom with metal inside.It can increase the SNR by 50%in the corrected reconstruction image while reducing the beam hardening artifacts greatly.