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Study On Analytical Image Reconstruction Algorithm Of High Speed And High Precision

Posted on:2012-04-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z W QiaoFull Text:PDF
GTID:1118330335951365Subject:Traffic Information Engineering & Control
Abstract/Summary:PDF Full Text Request
CT (Computed Tomography) is an excellent non-destructive diagnosis technology in medical and industrial science. Its essence is to reconstruct an object's tomographic image using its projection data. Due to the engineering demands of high resolution reconstruction, big object reconstruction and three-dimensional reconstruction, the data of CT images become larger and larger. So the reconstruction speed becomes a bottleneck.CT testing for precise products needs a very high precision and how to reconstruct a CT image directly is also a key and challenging task in CT engineering. This dissertation focuses on reconstruction speedup, precision improving and objective reconstruction.Firstly, the discretization formulas of FBP algorithm, proved by using signal processing theory and definite integral's definition, were studied, in which there are two key parameters, projection sampling interval and angle sampling interval. Numerical calculating method of definite integral was studied and a precise back projection method based on the Sampson formula was proposed. Simulation proved that the linear interpolation method is better than the spline interpolation. And a qualitative explanation was also given.On the base of analyzing the characteristics of the ramp filter, a design principle of the ramp filter was proposed. The impact of spectrum window-adding and time domain window-adding on reconstruction were analyzed. A length selection method for the unit impulse response of the ramp filter was proposed. A novel calculation method for the central value of the unit impulse response of the ideal ramp filter was adopted. The simulation results demonstrate that the exponent window is the best for spectrum domain and the rectangle window is the best for time domain. There is not air artifact in CT image when the length of the unit impulse response is 2(?)N-1.According to the characteristic that the projection and the unit impulse response are both long sequences, arithmetic Fourier transform (AFT) and fast Hadamard transform (FHT) were proposed respectively aiming to speedup methods for filtering process. Simulation results shows that the AFT-filtering method is faster than the FFT-filtering method about 30% and the FHT-filtering method is faster than the FFT-filtering method about 50%.Three speedup methods were studied. One is that the projection was interpolated to smaller intervals and the zero-order interpolation method was adopted for back projection. And one is that a passive ray-driven method was used for back projection. And the last one is that based on the strategy of "time advantage based on space occupancy", the values of the trigonometric functions were stored in advance to avoid complicated trigonometric calculations. Then a hybrid speedup method was proposed. Simulation results show that the method is faster than the traditional method for more than 4 times.The conception of objective reconstruction was proposed based on analyzing the conception of characteristic reconstruction. Three implementation methods were achieved, i.e., approximate method, precise method of space domain and precise method of spectrum domain. Practical experiments illustrate that the effect of the approximate method is not satisfactory and the others are effective, which can avoid effectively the impact of the not-white noise on CT image processing.For the analytical image reconstruction, speedup methods, precision development methods and objective reconstruction methods were studied in detail. The research results may provide an effective promotion on present analytical image reconstruction methods.The dissertation consists of eight chapters, with 58 figures,25 tables, and 110 references.
Keywords/Search Tags:Image reconstruction, Analytical method, Speedup, Precision, Interpolation, Filter, Objective reconstruction
PDF Full Text Request
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