Non-axisymmetric Field Of Ct With 3d Reconstruction

The exact measurement using optical theory is the primary method in the field of measure and testing, and it is one of the advanced technologies of the time. Since 1960, photoelectricity Measurement Technologies take great development in testing methods, principle, accuracy, efficiency, as well as in adaptable fields with the advent and development of laser technique, optical wave-guide technique, photoelectron technique, fiber technique and computer technique, along with the advent and development of Fourier optics, modern optics, duality optics and microcosmic optics, among these photoelectricity Measurement Technologies, holographic CT is one of the most rapidly- developed and the most abroad-applied technologies. Thereupon CT reconstruction of three dimensions is a basic form of Holography interferential Measurement technology.The difficulty of CT reconstruction increases in non-medicinal fields, for the reason that the short action time and the limited operator domain of the physical fields being measured. On the one hand, because of the short action time, it is impossible to get enough time to circumvolve instruments or to circumvolve the physical fields being measured so as to scan in all directions, so the physical fields can only be measured through several instruments; on the other hand, because the physical fields are partly screened or the operator domain is too limited, the measurement directions are limited, too. Hence reconstruction of few projections and reconstruction of limited rage initiate correspondingly. In addition, in consideration of cost factor, only few instruments can be used in the measurements. It amounts to this: in the instance of probability for given reconstruction accuracy, it is the expectancy to try to decrease the number of scanning directions, to facilitate the speed of reconstruction to accomplish the purpose of real-time measurement.Based on quantities of document retrieving, this thesis absorbs, summes up, and makes use of the findings of CT technology, optical measurement technology, image processing technology and information technology, benefits from modern theory of the influence by the view- directions and the sample-horizon choosing.The principle and calculating method of holographic CT and image reconstruction theory are introduced briefly in this thesis. Then, simulated study on calculating the axis symmetry media's deflection index is made by computer. Andthen, reconstructed study on calculating the axis symmetry media's deflection index is made by computer, compared the result with the axis symmetry media which is simulated, analyze the shortcoming of the reconstruction method. As an practical example4, a lamp of the 3-D distributing measurement of atmosphere refractive index is presented using holographic CT technology and the reconstruction of the lamp is given. The theoretical knowledge and simulation study both shown that when the edge of the physical field is not zero, the result of reconstruction of the physical field with Bair method 4s quit different from the real physical field. Therefore, a bigger error is brought if reconstructing any axis symmetry physical field with the Barr method without analysis.Two construction methods for fewer views from limited range—ART and SART are studied, and simulated a physical field's views whose variation of deflection is equal to double-Gauss function, and then reconstructed it, and still analyzed the accuracy of the reconstruction methods.After study and analysis on the theory of ART and SART, and after analysis the properties resulted from their theory root cause, A modified simultaneous algebraic reconstruction method is presented, which is based on ART, this method takes into account both the pixel itself and the pixels close by it which are crossed by the same ray. The theoretical knowledge and experimental research shows that this method can increase the reconstruction speed.Based on SART, a modified simultaneous algebraic reconstruction method is also presented, which takes into account both the density of pixel and the ray length across it in the error distribution. This reconstruction method can solve the edge distortion of both ART and SART effectively and makes an encouraging improvement in reconstructed images quality with sparse data. Even in the reconstruction of fewer views from limited range (In this thesis, the number of views is only four), good images can be obtained by choosing proper views. That is to say, the maximum error can be less than 5% and the average error can be less than 1%.