Edge detection method of retinal optical coherence tomography images based on immune genetic morphology
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摘要: 提出了基于免疫遺傳算法的形態學自適應結構元素生成算法,并將其用于光學相干斷層成像(optical coherence tomography,OCT) 圖像中視網膜組織邊緣檢測. 首先將圖像進行去噪和粗分割的預處理,并將圖像劃分為若干子圖像; 其次對每一子圖利用免疫遺傳算法求取自適應結構元,初始隨機生成固定長度的二進制數串作為抗體,并將其轉化為結構元素格式,以圖像二維熵定義抗體適應度,根據子圖像本身結構特征信息,尋找最優抗體結構元素; 最后利用尋優得到的各結構元素對子圖進行形態學邊緣檢測,合并各子圖的分割結果,實現整體圖像目標邊界提取. 實驗結果表明了該方法在圖像目標邊界提取的有效性.Abstract: Optical coherence tomography (OCT) is an indispensable tool used for the diagnosis and identification of ocular fundus disease and nondestructive, rapid, and high-resolution imaging of the living retinas. The attendant research focuses on the development of computer-aided methods to help ophthalmologists make judgments regarding the morphological changes of retinal tissue and acquire tissue characteristic parameters. Realizing the segmentation of retinal tissue in OCT images is the key aspect of this kind of research. Mathematical morphology, which has been widely used in the fields of image detection, shape analysis, pattern recognition, and computer vision, uses different structural elements to measure, extract, analyze, and identify image targets. However, traditional morphological structure elements cannot be adaptively changed on the basis of the structural characteristics of the images. In this study, an algorithm for generating morphological adaptive structural elements was proposed on the basis of an immune genetic algorithm, which the detection of retinal tissue edges in optical coherence tomography (OCT) images was applied. First, the image is preprocessed by denoising and coarse segmentation and then the image is divided into several sub-images. Second, the adaptive structure elements are computed using an immune genetic algorithm for each sub-image. A string of binary numbers of fixed length is initially randomly generated as an antibody and then converted into a format of structural element. The fitness of an antibody is defined by the two-dimensional entropy of the image and the optimal antibody and structural elements are identified according to the structural characteristics of the subimage itself. Finally, with these optimal structural elements, morphological edge detection is performed to obtain the segmentation results of each sub-image combined with those of each sub-graph to realize the extraction of the target boundary of the whole image. The experimental results show the proposed method to be effective in the boundary extraction of images.
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圖 3 視網膜邊界提取過程. (a) 原圖; (b) 去噪預處理; (c) 視網膜區域粗分割; (d) 圖像分塊; (e) 自適應結構元與邊緣檢測; (f) 最終分割結果
Figure 3. Extraction process of retinal boundary: (a) original image; (b) de-noising preprocessing; (c) rough segmentation of retinal region; (d) image segmentation into blocks; (e) adaptive structure element and edge detection; (f) final segmentation result
圖 4 多種邊界提取方法結果比較. (a) 原圖; (b) 去噪預處理; (c) 專家手動分割結果; (d) 尺度M = 3結構元; (e) 尺度M = 5結構元; (f) 多尺度結構元; (g) Canny; (h) GTDP; (i) IGM; (j) IGSM
Figure 4. Comparison of multiple boundary extraction methods: (a) original image; (b) de-noising preprocessing; (c) expert manual segmentation results; (d) structure element scale M = 3; (e) structure element scale M = 5; (f) multiscale structural element; (g) Canny; (h) GTDP; (i) IGM; (j) IGSM
表 1 多種邊界提取方法品質因數評價結果
Table 1. Partt quality factor evaluation results by multiple boundary extraction methods
邊界提取方法 品質因數,R/% Single_3 88. 31 Single_5 75. 79 Multi 84. 71 Canny 43. 05 GTDP 84. 7 IGM_3 89. 85 IGM_5 85. 9 IGSM_3 90. 23 IGSM_5 87. 23 表 2 視網膜組織量化結果
Table 2. Quantitative results of retinal tissue
邊界提取方法 區域 A/S1 A/S2 A/S3 A/S4 A/S5 T/S1 T/S2 T/S3 T/S4 T/S5 專家手動分割 NSL_R 1524 928 90 1051 1680 26.74 14.28 2.31 16.17 29.47 NSL_G 932 1309 878 1256 893 16.35 20.14 22.51 19.32 15.67 RPE 600 730 468 768 614 10.53 11.23 12 11.82 10.77 Single_3 NSL_R 1502 923 106 1055 1652 26.35 14.20 2.72 16.23 28.98 NSL_G 948 1320 861 1254 912 16.63 20.31 22.08 19.29 16.00 RPE 454 714 468 759 606 7.96 10.98 12.00 11.68 10.63 Single_5 NSL_R 1377 777 43 1012 1529 24.16 11.95 1.10 15.57 26.82 NSL_G 1069 1452 922 1823 1029 18.75 22.31 23.64 19.74 18.05 RPE 459 579 388 637 485 8.05 8.91 9.95 9.80 8.51 Multi NSL_R 1506 930 117 1056 1652 26.42 14.31 3.00 16.25 28.98 NSL_G 944 1302 852 1252 910 16.56 20.03 21.85 19.26 15.96 RPE 587 724 468 761 607 10.30 11.14 12.00 11.71 10.65 Canny NSL_R 1522 950 162 1085 1669 26.7 14.62 4.15 16.69 29.28 NSL_G 913 1275 787 1218 884 16.02 19.62 20.18 18.74 15.51 RPE 609 729 492 768 617 10.68 11.22 12.62 11.82 10.82 GTDP NSL_R 1151 1098 814 1240 1659 26.51 16.89 20.87 19.08 29.11 NSL_G 930 1131 156 1063 896 16.32 17.40 4.00 16.35 15.72 RPE 595 725 468 761 619 10.44 11.15 12.00 11.71 10.86 IGM NSL_R 1501 921 105 1059 1652 26.33 14.17 2.69 16.29 28.98 NSL_G 948 1323 862 1251 911 16.63 20.35 22.10 19.25 15.98 RPE 582 713 468 759 606 10.21 10.97 12.00 11.68 10.63 IGSM NSL_R 1501 923 107 1059 1651 26.33 14.20 2.74 16.29 28.96 NSL_G 949 1322 860 1251 913 16.65 20.34 22.05 19.25 16.02 RPE 584 713 468 759 606 10.25 10.97 12.00 11.68 10.63 表 3 多種邊界提取方法與專家結果量化平均相對誤差比較(以面積為例)
Table 3. Comparison of the average relative errors determined by multiple boundary extraction methods and expert results (as an example of area)
邊界提取方法 Single_3 Single_5 Multi Canny GTDP IGM IGSM ARE 0.0383 0.1586 0.0303 0.0751 0.6385 0.0241 0.0256 259luxu-164 -
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