Research On Low Radiation Dose CT Reconstruction

Since the birth of Computed Tomography (CT) imaging technology, after decades ofdevelopment, the CT scanning speed is faster and the reconstruction time is shorter, whichpromote CT in clinical applications, but the CT radiation dose is also increasing. Nowadayspeople pay more and more attention to the potential hazards of the human body caused by CTradiation dose. In order to reduce CT radiation dose, many CT researchers, manufacturers andclinical operations staff had made great efforts. Lowering the tube current intensity (low-doseCT) and reducing the number of samples (sparse angle CT) are applied, both of whichdamage projection data completeness and lead to serious degradation of the quality of thereconstructed image by traditional reconstruction algorithm directly. Therefore, how tominimize x-ray exposure to patients while ensuring the quality of the reconstructed image hasbecome a hotspot in the research of CT. The reconstruction algorithms of low-dose CT imageand sparse angular CT image are mainly studied in this thesis as follows:(1) Low-dose CT reconstruction based on combination denoising in wavelet domain.Low-dose CT projection data containing stronger noise, will lead to degradation of imagereconstruction. Therefore the noise in the projection data should be effectively filtered, and atthe same time it is need to protect the image detail features as much as possible, to solve thisproblem, combination denoising algorithm in wavelet domain is proposed. According to theanalysis noise statistical characteristics of low-dose CT projection data in wavelet domain,using LAWML denoising algorithm to filter noise, and according to the estimation ofprojection data to design experience Wiener filter for the original low-dose CT projection datafiltering, realizes the combination denoising. The filtered projection data can reconstruct theclear CT images by using the traditional FBP algorithm. Simulation results show that thedenoising algorithm, combination of suppressing noise ability is improved, can preserve moreimage detail characteristics.(2) Sparse angle CT reconstruction based on compressed sensing. For thetime-consuming disadvantages of iterative reconstruction algorithm for sparse angle CT,medical image gradient sparse nature is introduced to accelerate the speed of convergencewhich only needs20angle projection data to accurately reconstruct image. To deal with thelimited capacity of reducing the radiation dose, a sparse angle and low-dose CT reconstruction method, combined with low-dose CT and sparse angle CT reconstructionmethod, is proposed to reconstruct a clear image from60angle of low-dose CT projectiondata, greatly reduce the CT radiation dose.