Retinal fundus photographs are employed as standard diagnostic tools in ophthalmology. Serial photographs of the flow of fluorescein and indocyanine green (ICG) dye are used to determine the areas of the retinal lesions. For objective measurements of features, the registration of the images is a necessity. In this paper, we employ optimization techniques for registration with the help of 2-parameter translational motion model of retinal angiograms, based on non-linear pre-processing (Wiener filtering and morphological gradient) and computation of the similarity criteria for the alignment of the two gradient images for any given rigid transformation. The optimization methods are effectively employed to minimize the similarity criterion.
The presence of noise, the variations in the background and the temporal variation of the fluorescence level pose serious problems in obtaining a robust registration of the retinal images. Moreover, local search strategies are not robust in the case of ICG angiograms, even if one uses a multiresolution approach.
The present work makes a systematic comparison of different optimization techniques, namely the minimization method derived from the optical flow formulation, the Nelder-Mead local search and the HCIAC ant colony metaheuristic, each optimizing a similarity criterion for the gradient images. The impact of the resolution and median filtering of gradient image is studied and the robustness of the approaches is tested through experimental studies, performed on macular fluorescein and ICG angiographies.
Our proposed optimization techniques have shown interesting results especially for high resolution difficult registration problems. Moreover, this approach seems promising for affine (6-parameter motion model) or elastical registrations. 相似文献
As our world becomes increasingly multicultural in nature, multilingual skills constitute an everyday phenomenon in schools. Since most of the second-language research has focused on school-age students, more research had to be conducted with language-minority students at the kindergarten level in order for psychologists and educators to develop effective and efficient systems for evaluating and tracking the developmental status of young language-minority children. The purpose of this study was to investigate the potential usefulness of a standardized continuous progress measure, the Picture Naming Individual Growth and Development Indicator, to longitudinally assess language development in 23 language-minority children, as well as in 13 native English-speaking children. Results indicated that we could use the Picture Naming Individual Growth and Development Indicator to detect differences in first-language and second-language development in language-minority children, as well as to detect differences between the two groups of children in their expressive English-language skills. 相似文献