【正文】 stroyed and the thinning effect decreased. On the basis of the above analysis, Mei Yuan and other authors proposed the concept of position template, which took advantage of the elimination template of document [1], abandoned the preservation template and bined the judgment whether the point satisfied the elimination template will be preserved with the situation of its neighborhood point. Figure 5 is the schematic diagram about the neighborhood of current point. Figure 5. The neighborhood diagram of point p The thinning algorithm based on improved position template doesn39。 q12=0 amp。 q12=0 amp。 q10=0 amp。 q7=0 amp。 q14=0) (6) (q3=0 amp。 meanwhile, the speed is also enhanced. III. DETECTION OF CEREBRAL ANEURYSM BASED ON SKELETON TREE After obtaining the skeleton tree by thinning the cerebral vascular image, a certain width of the blood vessel bees only a pixel width of the skeleton and cerebral vascular image bees a curve of single pixel. Through the extraction of skeleton structure elements, the detection of cerebral aneurysm is based on the length of branch element on skeleton tree. A. Extraction of Skeleton Structure Elements 1) Extraction of key point element Key points present to the places where dramatic changes have been taken place in skeleton characteristics, which includes endpoint and bifurcation. Endpoint is the starting point on the part of skeleton tree, and p is endpoint if there has only one skeleton point in the eight neighborhood of the current point p, just as a,c,d and f shown in Figure 6. Bifurcation is the converging point of different parts of skeleton tree, and p is bifurcation if there has three or more skeleton points in the eight neighborhood of the current point p, just as b and e 16 shown in Figure 6. Figure 6. Skeleton structure elements representation 2) Extraction of branch element Branch element is the skeleton segment, which connects two key points and does not pass by the third key point of the skeleton. If the key points are not endpoint, it is called inner branch, otherwise, outer branch. In this paper, branch element we discussed is outer branch. The extraction method of branch element starts with endpoint: Find a endpoint firstly, and track it along until the next point is bifurcation. The skeleton segment which starts with endpoint and ends with bifurcation is the branch element. B. Detection of Cerebral Aneurysm Based on Branch Element A conclusion gained by analyzing the morphology of cerebral aneurysm: how to detect the branch structure of cerebral vascular skeleton is the key to the detection of cerebral aneurysm. There are three kinds of branch structure of skeleton map which are caused by cerebral aneurysm, burr and normal blood vessels respectively. So cerebral aneurysm can be detected from the three kinds of branch structures by judging branch structure caused by cerebral aneurysm. In this paper, by doing depthfirst traversal search on skeleton tree, the pixel length of branches will be the basis of detection. The specific steps was conducted as follows. (1) Traverse the entire skeleton tree from the root of skeleton tree, and mark the pixels which have been visited。s a betterperforming algorithm, but the contrast in the experiment appears different effects of skeleton extraction, Figure 8(a) with less burrs of skeleton, while Figure 8(b) with more burrs in skeleton. After a large number of experiments, the reason is found that the emergence of burr is largely due to the inadequate binary effect of blood vessels, noise jamming and other reasons. Burr in the vascular skeleton structure also manifested as the same branch structure, so it affects on the precision of cerebral aneurysm detection greatly. As shown in Figure8, the position marked by pane is the detected cerebral aneurysm part. The detection effect in Figure8 (a) is good, while two wrong regions exist in Figure 8(b). In this paper, the cerebral aneurysm detection method based on skeleton features can basically determine the position of cerebral aneurysm. Although the length of branch used as a basis will encounter the interference of skeleton burr and exist incorrect detection, the significance of cerebral aneurysm detection is to reduce the numbers of detection objectives of cerebral aneurysm and provide data premise for recognition. How to do binarization effectively, provide best foundation to skeleton extraction, and reduce adverse effect on cerebral aneurysm detection caused by burr will be the future research emphasis. V. CONCLUSION This paper analyzes the morphological characteristics of cerebral aneurysm, researches OPTA and its improved algorithms deeply and applies them to the extraction of skele