| 英文摘要 | Through over 30 years development, medical CT (Computed Tomography) imaging technology has achieved substantial enhancement both in efficiency and precise,from 2-D (Two Dimensional), in the modest begin by use of which to pile up toform a 3-D (Three Dimensional) volume image, to virtually 3-D cone-beam reconstructionin recent years.In the middle of 1980's, a novel 3-D reconstruction method, FDK algorithm, has beendeveloped, which was a generalized FBP method from 2-D to 3-D and played a criticallyimportant role not only in theoretical consideration but for commercial application, although that was an approximate method. After that, many researchers were involved tostriving for virtually 3-D reconstruction, since that is a necessity for cone-beamreconstruction causing a bigger cone angle in the condition of multi-row detector.More considerably, modern medical (clinical) standard requires as less as possible radiation towardsnormal tissues surrounding the diseased region, which would reduce unnecessary harmto the healthy organs, therefore, it is in an urgent need of a specific reconstruction methodfor a special ROI (Regions of Interest), required to accommodate incomplete projectiondata with serious truncations. Such a requirement, on the other hand, is also reasonablefor the emerging imaging-radiotherapy CT machine bringing referable images as by products in the radiotherapy process.The main contributions in this PhD dissertation are as following,Presented a serial of chord-based cone-beam reconstruction algorithms, some of whichcan obtain exact ROI images from projection data with serious longitudinal and transversetruncations; Conducted a complete evaluation for the algorithms above, including the noise properties and reconstruction precise. Additionally, we have also achieved a quantitativedescription for the noise property in each reconstruction step, embracing weightingstep, backprojection step and filtering step; Introduced a spherical detector and the corresponding uniform sampling method on the detector and reconstruction algorithm,which could reduce the cross-talk absorption in the adjacent bins in the detector; Presented a general reconstruction algorithm for a generalized line-circle scanning trajectory, which is more specific for ROI imaging; Introduced a conceptual way to understand the relations between the Katsevich algorithm and Zou-Pan algorithm; Implemented chord-based local tomography, which can obtain the exact contourof ROI as a valuable reference for clinical diagnosis. |
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