Medical X-ray CT Few-view Imaging Optimization Algorithm And Motion Artifact Correction

In 2011,National Academy of Sciences,National Institutes of Health of United States etc.proposed the Precision Medicine.In 2015,President Obama officially approved the Precision Medicine project to promote the development of personalized medicine.In order to fully implement the related tasks of “National medium and longterm science and technology development plan outline(2006-2020)”,China proposed the special emphasis of “Precision Medicine research” which will build the curative effect evaluation and analysis system of innovative research of disease diagnosis,treatment and so on.Therefore,China launched the national key research project of “The special emphasis of digital medical equipment research and development” at the beginning of the thirteenth five years' development plan of China and the advanced imaging technology is one of the important research contents of this plan.Undoubtedly,nowadays,the new principle,new technology and new method of medical X-ray CT will become the indispensable research hotspot and advanced technology towards the precision medicine.According to the recent studies,the low dose helical X-ray CT screening is an effective way to find the lung cancer at early stage which could reduce 20% of lung cancer death compare with the conventional chest radiography.Therefore,X-ray CT plays an important role in the medical diagnosis.For this purpose,author completed this dissertation study work with two years' domestic and two years' overseas professors' supervision,who receive a scholarship “Chinese Building for High-level University graduate programs” granted by China Scholarship Council(Admission No.20146050068,File No.[2014] 3026).The study work was partially supported by U.S.NIH/NIBIB Grant R01 EB016977,U01 EB017140,National Natural Science Foundation of China(No.61201346,No.61401049),graduate innovation projection of Chongqing(CYB14024)etc.Although medical X-ray CT technique plays an important role in medical clinical diagnosis,X-ray is a kind of ionizing radiation which is harmful for human body and even increase the patients' risk of getting cancer.With the breakthrough points of low dose,few view,motion artifacts of medical X-ray CT key technology,the research contents of this thesis mainly include:(1)Fully and systematically studied the medical X-ray CT imaging principle,structure,methods and techniques all over the world,simultaneously studied the medical X-ray CT imaging theory,the development of equipment and techniques.Elaborated the challenges to find the lesions in patient body which are to reconstruct the high-quality CT images in the presence of interference and restriction,to reduce the X-ray radiation dose of human body by maintaining the quality of reconstructed CT images or to development other diagnosis methods to reduce the radiation dose.Based on this,established a research approach of low dose,few view,motion artifacts reduction medical X-ray CT key techniques.(2)Studied the medical X-ray CT reconstruction methods with few views.In order to reconstruct the high-quality CT images with few view,with Compressed Sensing theory and the principle that X-ray CT projection data is a typical sparse signal,we could reconstruct high-quality CT images with few-view projections by choosing a proper orthogonal transform.Based on this,in order to solve the insufficient sparseness of using L1 regularization in Compressed Sensing,we proposed a few-view CT reconstruction method with L1/2 regularization by introducing the L1/2 regularization into Compressed sensing.Compare with the commonly used L1 regularization,L1/2 regularization could better describe the sparseness of signal and could reconstruct high-quality CT images with few-view projections.On the other hand,in order to solve the disadvantage that conventional Total Variation only using one directional gradient information,we stuied the few-view CT reconstruction algorithm based on Multi-directional Total Variation.Compare with traditional few-view reconstruction algorithms based on Total Variation,Multi-directional Total Variation could provide gradient information in more directions which could guarantee the high-quality CT images with few-view projections.(3)Stuied a calibration phantom-free CT geometric parameter calibration method based on Locally Linear Embedding(LLE).Using the original projection data and reprojected projection of reconstructed images,update the geometric parameters with LLE.Based on this,calibrated the geometric parameters of fan-beam CT using the projection provided by Institute of High Energy Physics,Chinese Academy of Sciences.In the meantime,calibrated the geometric parameters of phase contrast CT system of Professor Ge Wang's lab,Rensselaer Polytechnic Institute.Both experiments calibrated precise geometric parameters and reconstructed high-quality CT images.(4)Studied a rigid patient motion correction method based on Locally Linear Embedding.In order to solve the problem that there is no simple and general rigid patient motion correction method,without external motion sensing equipments,we calibrate the patient motion parameters using re-projected projection of reconstructed images and Locally Linear Embedding which is a pure software based rigid patient motion correction method.We applied this method into patient motion correction in fan-beam CT and conebeam CT which reconstructed high-quality,motion artifacts-free CT images.The patient motion in cone-beam CT is the gerenal rigid patient motion problem.The patient motion correction method based on LLE could solve the general rigid patient motion problems.(5)Studied the super low-dose lung nodule quantification method based on active shutter stereo imaging system.In order to solve the problem that the conventional conebeam CT based lung nodule quantification method has high radiation dose and high cost,we proposed a lung nodule quantification method with few pairs of projection.By generating two projections of an iteratively placed ellipsoidal volume in the field of view and merging these synthetic projections with two original CT projections,we show the feasibility of measuring the position and size of a nodule by observing whether projections of an ellipsoidal volume and the nodule are overlapped from a human observer's visual perception through the active shutter 3D vision glasses.Based on this,we did the simulation and real experiment with lung CT images from Massachusetts General Hospital.The experiments indicate that this method could measure the position and size of lung nodule with the error under 1mm.This research work related to radiation dose,X-ray detection principle,parameter calibration of precision mechanical scanning system,optical stereo imaging,CT image reconstruction algorithm,digital image processing and optimization model etc.This research work combined the research work in many research fields which highlights the advantages of multidisciplinary.Therefore,the research work of patient based X-ray CT imaging key techniques not only has important and profound theoretical significance but also has more important potential practical value.