A New Method For Correction Of Radial Metallic Artifacts In CT Images

Computer tomography(CT)is one of widely used techniques in clinical practice.It uses X-ray beam to scan a part of human body and transmitted X-rays are received by the detector,then the measured signals are converted to digital information and processed by a computer.Eventually,we get the X-ray absorption value(called CT number)of each voxel of the human body.CT imaging characterizes the attenuation coefficients of X-rays of different tissues.CT imaging is simple and high density resolution.It can directly display the organs and lesions that X-ray film cannot show.However,the density range of the substance to be scanned is a problem that plagues CT imaging.In CT images,high-density objects,such as metal prostheses,surgical clamps,and dental fillings,can produce radial artifacts,called metal artifacts.These metal artifacts affect doctor’s diagnosis of diseases and interfere with dose calculations during radiotherapy.In order to solve the problem of metal artifacts in CT scans,a new method based on filtering in frequency domain is proposed for the correction of X-ray metal artifacts arising from dental fillings.The proposed algorithm converts radial artifacts into linear artifacts through polar coordinate transformation,and then carries out Fourier transform of the obtained linear artifacts to obtain spectral image.A two-dimensional image filter in the frequency domain is designed to filter out the linear artifacts.Finally,the corrected CT images are obtained by inverse Fourier transform and inverse coordinate transform.The algorithm does not need to perform forward projection or obtain the raw data from detector.It is simple and fast.It is able to not only reduce metal artifacts but also protect image edge information.In our study,CT images of 11 clinical cases were processed using the new method,and the results were quantitatively analyzed with standard deviation and mean difference of CT values.The results show that after the process,patchy metallic artifacts were reduced,and striped metal artifacts were removed.Compared with the existing spatial domain mathematical morphology algorithm,the proposed method is more effective to reduce the striped metal artifacts.In this study an interactive software was also designed for CT image processing based on MATLAB.It can performsome basic medical image processing functions and metal artifacts correction in CT images.It can quickly import DICOM files,browse and process CT images.It also supports modification,adding controls and improve the efficiency of imaging researchers.