Purpose: The purpose of this work was to develop and validate

Purpose: The purpose of this work was to develop and validate a computer-aided method for the 3D segmentation of lymph nodes in CT images. accuracy, 74150-27-9 manufacture 111 lymph nodes of mediastinum, abdomen, head/neck, and axillary regions from 35 volumetric CT scans were utilized. For accuracy analysis, lymph nodes were divided into three test sets based on lymph node size and spatial resolution of the CT scan. The average lymph node size for test set I, II, and III was 1056, 1621, and 501 mm3, respectively. Spatial resolution of test set II was lower than for test sets I and III. To generate an independent reference standard for comparison, all 111 lymph nodes were segmented by an expert with a live wire approach. Results: All test sets were segmented with the proposed approach. Out of the 111 lymph nodes, 40 cases (36%) required computer-aided refinement of initial segmentation results. The refinement typically required 10 s per lymph node. The mean and standard deviation of the Dice coefficient for final segmentations was 0.847 0.061, 0.836 0.058, and 0.809 0.070 for test sets I, II, and II, respectively. The average signed surface distance error was 0.023 0.171, 0.394 0.189, and 0.001 0.146 mm for test sets I, II, and II, respectively. The time required for locating the approximate center point of a target lymph node in a scan, generating an initial OSF segmentation, and refining the segmentation, if needed, is typically less than one minute. Conclusions: Segmentation of lymph nodes in volumetric CT images is a challenging task due to partial volume effects, nearby strong edges, neighboring structures with similar intensity profiles and potentially inhomogeneous density of lymph nodes. The presented approach addresses many of these obstacles. In the majority of cases investigated, the initial segmentation method delivered results that did not require further processing. In addition, the computer-aided segmentation refinement framework was found to be effective in dealing 74150-27-9 manufacture with potentially occurring segmentation errors. of lymph node to be segmented. Second, a directed spherical graph, whose center is located at c= (and edge set of lymph node with radius is a constant and chosen to be larger than the largest expected radius of lymph nodes. Let be the number of vertices of the spherical mesh. {For each mesh vertex pwith {1,|For each mesh pwith 1 vertex, , and vertex pin an equidistant fashion using linear interpolation. The line between center point cand vertex pis denoted as column represents already a sample point/node, whereas cis not utilized. The gray-value samples on the line between cand pform the elements with [0, 1, , (? 1)]. The number of elements per column is a constant and denoted as ? 1) represents the gray-value density sample 74150-27-9 manufacture at the location of vertex pcorresponds to gray-value sample point nodes in the graph. Considerations regarding the selection of sampling parameters and are as follows. Essentially, both numbers need to be adapted to the resolution of the CT image data. If is selected too small relative to image voxel size, the mesh 74150-27-9 manufacture will be too sparse and unable to represent the lymph node’s surface accurately. Conversely, if is chosen too large, the computation time will increase with no major benefits regarding segmentation accuracy. Similar considerations apply for 74150-27-9 manufacture the selection of and column are adjacent. A surface smoothness constraint between any two adjacent columns is utilized to specify the maximum allowable change/difference in surface node locations.14 Figure ?Figure22 depicts a 2D example of the graph generation. By constructing the graph as described above, spherical, elliptical, or slightly kidney-shaped lymph nodes can be segmented. In this context, the selection of an adequate smoothness constraint is of importance for our method. If the smoothness constraint is too small, the surface will not Rabbit polyclonal to Lymphotoxin alpha be able to follow the lymph node surface in some cases (e.g., elongated lymph nodes). On the other hand, if the smoothness constrain is too large, the resulting surface.

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