A new enhancement method is proposed based on the characteristics of fundus images in this paper. Firstly, top-hat transform is utilized to weaken the background. Secondly, contrast limited adaptive histogram equalization (CLAHE) is performed to improve the uneven illumination. Finally, two-dimensional matched filters are designed to further enhance the contrast between blood vessels and background. The algorithm was tested in DIARETDB0 databases and showed good applicability for both normal and pathological fundus images. A new no-reference image quality assessment method was used to evaluate the enhancement methods objectively. The results demonstrated that the proposed method could effectively weaken the background, increase contrast, enhance details in the fundus images and improve the image quality greatly.
目的探讨间断低氧预适应对大鼠肝大部切除术后残余肝脏合并缺血再灌注引发过氧化损伤的保护作用。 方法78只SD大鼠，用SPSS软件将其随机分为4组：假手术组（SO组，n=6）、肝切除组（PH组，n=24）、肝切除合并缺血再灌注损伤组（IR组，n=24）和间断低氧预适应组（IHP组，n=24）。以无创伤血管夹阻断IR组大鼠入肝血流后切除肝脏的左叶和中叶（约占全肝的70%），20 min后开放入肝血流，残余肝脏发生了缺血再灌注损伤。将IHP组大鼠暴露于10%的低氧环境中，每日持续1 h，连续进行1周，最后1次低氧暴露后行肝切除术（同IR组）。SO组大鼠在术后2 h取材检测，其余各组分别于术后2、6、12及24 h进行检测。检测血清转氨酶（ALT、AST）水平和肝匀浆组织中超氧化物歧化酶（SOD）活性及丙二醛（MDA）含量。 结果术后2 h，PH组、IR组和IHP组大鼠血清ALT和AST水平均高于SO组（P<0.05）。在术后6、12和24 h，IHP组大鼠血清ALT和AST均高于PH组，但低于IR组（均P<0.05）。与IR组相比，IHP组大鼠术后各时间点残余肝脏中SOD活性明显升高，而MDA含量则显著降低（均P<0.05）。 结论间断低氧预适应对残余肝脏缺血再灌注损伤具有保护作用，其机理可能与提高肝脏的抗氧化能力有关。