To facilitate early detection and removal of colonic polyps, we have developed a method to present the whole colon surface in a single 2D image. To improve detection sensitivity and lower false positives while using the 2D image, we utilize curvature-vector pair and curvature-images to construct a candidate-point image to indicate possible locations of polyps in the 2D image. Planes perpendicular to the centerline are generated. On each plane, equiangularly spaced radial rays are generated, which intersect the colon surface, generating sample points. The centerline index of the planes and the angular index of the radial rays on each plane define the x and y coordinates of a 2D array, respectively. At each sample point, four curves are constructed along the x, the y, and the two diagonal directions, for which four curvatures are calculated. The curvature vectors which pointing into the lumen are set to zero. Then, at each sample point, the values of the maximum and minimum curvature are assigned to the corresponding element in the 2D array. Using this 2D array and a two-step thresholding method, a so-called candidate-point image, which indicates possible locations of polyps, is generated. In the two-step thresholding method, the thresholds are determined by using a five training colon-data sets. This candidate-point image can be used in conjunction with other analyses in polyp detection.
CT colonography (CTC) is a new technology, which permits endoscopic-like evaluation of the mucosal surface. Recently, an electrical field based approach was developed to unravel the colon in spiral CT image volumes, that is to digitally straighten then flatten the colon using curved cross-sections. In this paper, we report (1) an exact and computation- intensive algorithm for straightening the colon using curved cross-sections, and (2) an approximate but computationally efficient straightening algorithm. In the direct straightening algorithm, each curved cross-section of the colon is defined by electrical force lines due to charges distributed along the colon path, and constructed by directly tracing the force lines. In the fast straightening algorithm, only representative force lines are traced that originate equiangularly from the current colon path position, while other force lines are interpolated from the traced force lines. The experiments are performed with both phantom and patient data. It is demonstrated that straightening the colon with curved cross-sections facilitates visualization and analysis, has potential for use in CTC; and the speed of the interpolation based straightening algorithm is practically acceptable, which is about 40 times faster than that of the direct algorithm.
It is the chief difficulty of laser cladding metal-ceramics layer that cracks are liable to emerge. The processing technology and coating materials are studied to resolve the problem. Firstly, according to the calculating of temperature field distribution and analysis of thermal stress in the cladding procedure, it is considered that the scanning velocity of laser beam and initial temperature are the main technological factors of crack emergence. On the other hand, the gradient distribution of ceramic hard phase is carried out and transition layer is put in between cladding layer and substrate. The results of SEM and microhardness test show, the hardness changed smoothly from surface to substrate, coating layer is dense and free of cracks.
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