Research On Image Processing Methods For Direct Digital Radiography System

With the rapid improvement of the daily life, more and more people begin to pay attention to the health care. The state has also invested a lot of manpower and material resources to promote the health care standards. Medical image diagnosis is a kind of routine medical examinations. It has been widely used in the diagnosis and treatment of disease and body check-up of the enterprises and institutions or the individuals. Especially, the X-ray imaging examination is frequently used. With the development of the materials science and the computer technology, the X-ray imaging technology has entered the direct digital radiography (DR) era from the original film. It takes faster imaging speed and better image quality, and also the digital X-ray imaging has brought out some new problems. For example, how to control the exposure system automatically? What's the conversion from the X-ray to the electronic signals? The imaging system must be calibrated. And the digital X-ray images need to be post processed. By studying the imaging method of the DR system, the quality of the digital X-ray image can be improved, and the diagnosis and treatment of diseases in the hospital will be boosted. It is also a reference for the study of other medical imaging models. More over, it is the foundation for the computer-aided diagnosis in the future. Evidently, it is very important to study the imaging method for the DR system.Based on the imaging process of the DR system, several key problems of the relevant part have been studied in this thesis. Such as the control of the high-voltage generator, image acquisition and calibration, image post-processing. Our goal is to achieve optimal control of the DR system and get better quality X - ray images. The high-voltage generator is the power-supply device for the X-ray, which needs to have good cooperation with the computer system so as to control the exposure process and exchange exposure parameters for the X-ray imaging. The X-ray arrives at the receiving device after transmission involving the human body. Based on the imaging principle and material properties, the image acquisition and image correction mainly solve the energy conversion problems from the X-ray to the computer. After having achieved the X-ray images, we utilize a variety of image processing algorithms to further improve the image quality, so as to satisfy the applications. We have carried out in-depth research on the DR imaging system, and several productions have been achieved as following:(1) A proposal is presented to improve the original complicated control of the exposure parameters on the DR system. We redesigned the interface circuitry of the high-voltage generator by using RS-232 serial COM port. The data and signals are transmitted between personal computer and high-voltage generator with serial mode. A program package is designed to realize the control of the exposure parameters for high-volt generator of DR on the PC machine. Experiment results shown that the proposed console operates steadily and it is possible to provide a more convenient operation console for the direct radiography system.(2) The signal control strategy in a Matrox Meteor II/Camera Link card-based DR image acquisition system has been studied. We designed the processing flow for status control and data process of the flat panel. A line interval scan and area exchange algorithm is presented to process the original image data acquired from the detector array. The problem on the adjustment of the abnormal original image has been solved successfully, and a program is developed for DR image acquisition, display and storage. Experimental results on water models and human bodies show that the methods described here were correct and credible, and the digital x-ray images were valid. It has been applied in the clinical practices of the DR system.(3) Based on the principle of DR imaging and the image acquisition process, we take our point of view on the energy conversion perspective from the X-ray to the computer. A detailed study has been carried out on the image noise produced by the inhomogeneity of the X-ray field and the flat panel detector pixel response. According to the various factors, corresponding correction methods have been introduced. Finally, for the uncertainty of the X-ray system at use, we extract a new theory for the overall correction, which has been designed and implemented as an effective field operation algorithm.(4) The problem of several DR images stitching has been studied. An image registration algorithm based-on feature points is presented. And a weighted average algorithm is used to solve the image fusion process. There are many embarrassments in the stitching process, such as light difference, too many similar feature points, big displacement, and long time for process. In our approach, these problems are well-handled. The programme has been complied to carry out the algorithms. We have taken the X-ray images for objects, fish and the human body. Experimental results show that the methods described here were correct and credible, and the composed digital x-ray image was valid. It can be applied in the design of a direct digital radiography system.(5) The exposure region characteristics of the X-ray image have been studied. An automatic algorithm has been introduced for detecting and cutting the exposure region of the image, which reduced the image storage space and facilitate the doctors operation and diagnosis. On this basis, a scalable image enhancement algorithm was imported, which makes better improvement in the overall and details in the image. The image has been further enhanced. Finally, we optimized the so-called window width and window level algorithm to display the images.