【文章內(nèi)容簡介】 aneurysm in DSA. This paper analyzes morphological characteristics of cerebral aneurysm, obtains the topological skeleton tree via the improved thinning algorithm, then does depthfirst traversal search on skeleton tree, and lastly detects the position of cerebral aneurysm. II. OPTA ALGORITHM OPTA(Onepass Thinning Algorithm) is a typical templatebased image thinning algorithm, whose core is thinning processing by the application of elimination template and preservation template. OPTA is an iterative process. If the current point satisfies the elimination template and doesn39。t satisfy preservation template, it will be eliminated. Otherwise, it will be preserved. The original image is traversalled continuously until no point satisfies the above condition. The main improvement upon OPTA is proposing new elimination template and preservation template according to the defect of thinning effect and thinning speed of original algorithm. Among them, the most typical documents are [1~3]. It is found by the authors of document [1] that original OPTA has the disadvantages of inplete thinning, more burr and inadequate smooth. Much improvement has been undergone on elimination template and preservation template in the improved algorithm. Figure 2 and Figure 3 are the improved elimination template and preservation template respectively, among which shadow pane is current point. 13 Figure 2. The elimination template of document [1] Figure 3. The preservation template of document [1] Because the condition for preservation template in the algorithm of document [1] is too loose, the effect of right oblique line produces easily while analyzing the images, which made iteration times increase and the speed slow. Therefore, new preservation template was proposed on the basis of document [1] and they were increased to 9. From Figure 4, the condition of preservation template bees more strictly, which solved the effect of right oblique line well, and the speed has been improved immensely. 14 Figure 4. The preservation template of document [2] With the development to the depth, Mei Yuan and other authors found that the effect of right oblique line was solved well by the algorithm of document [2] and the speed has been improved immensely. But because of its enhanced preservation condition, the breakpoints appeared. As a result, the topology and connectivity of original image has been destroyed 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。t need matching operation for preserve template. Every elimination template corresponds to one case of every neighborhood points39。 pixel value, and it uses logical operation “amp?！?and “||” to plete the judgment whether current point will be preserved. The following 8 conditions correspond to 8 elimination template marked with a~h in Figure2. If it satisfies elimination template and 15 corresponding elimination condition, this point will be deleted. Otherwise, it will be preserved. (q4=0 amp。 q5=0 amp。 q6=0 amp。 q7=0) || (q5=1 amp。 q6=1 amp。 q12=0 amp。 q13=0 amp。 q14=0) (1) (q2=1 amp。 q4=0 amp。 q7=0 amp。 q9=1 amp。 q11=0) || (q2=0 amp。 q9=0 amp。 q12=0 amp。 q13=0) (2) (q5=0 amp。 q6=1 amp。 q7=0 amp。 q11=0) (3) (q2=0 amp。 q9=1 amp。 q13=0 amp。 q14=0) (4) (q8=1 amp。 q10=0 amp。 q13=0 amp。 q14=0) || ( q8=0 amp。 q10=1 amp。 q12=0) (5) (q3=0 amp。 q4=0 amp。 q7=0 amp。 q10=1) || (q3=1 amp。 q7=0 amp。 q10=0 amp。 q11=0) || (q8=1 amp。 q10=0 amp。 q13=0 amp。 q14=0) || (q8=0 amp。 q10=1 amp。 q13=0 amp。 q14=0) (6) (q3=0 amp。 q4=0 amp。 q7=0 amp。 q10=1 amp。 q11=0) || ( q3=1 amp。 q7=0 amp。 q10=0 amp。 q11=0) (7) p=1 (8) Among them, p is the current point and Figure 5 shows q1~15. Though at present, improved OPTA is only applied to the thinning of fingerprint image [4~8]. This paper applied the above and improved OPTA to skeleton extraction of cerebral vascular image. By many experiments, we found that the burr of vascular skeleton extracted by original OPTA is a bit more, so it cannot be used in the detection of cerebral aneurysm. The effect of document [1