Browsing by Author "Serranho, Pedro"
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- Adaptive complex diffusion noise despeckling for 3D OCT DataPublication . Bernardes, Rui; Maduro, Cristina; Serranho, Pedro; Dinis, João; Cunha-Vaz, JoséPurpose: To demonstrate the performance of a recently proposed despeckling filter when extended to 3D in OCT data. Methods: A new formulation for a complex diffusion filter was recently proposed [1] being adaptive in time and adjusting parameters to data, facilitating diffusion in the vitreous and reducing it in the retina to preserve tissue information. This new formulation outperformed, both quantitatively and qualitatively, currently existing filters, while at the same time was computationally more efficient attaining the same despeckling level in 34% of the computing time. We have now extended it to perform 3D OCT despeckling achieving a significant improvement in noise removal. We have resorted to a mathematical based synthetic OCT scan in order to assess quantitative results in 3D. In addition, we have applied this 3D filter to a set of 72 eye scans, from healthy volunteers (20), diabetic retinopathy (20), cystoid macular edema (2), age-related macular degeneration (20) and choroidal neo-vascularization (10), who underwent high-definition Cirrus OCT (Carl Zeiss Meditec, Dublin, CA, USA) using macular cube protocols (200x200x1024 and/or 512x128x1024). Results: The extension from 2D to 3D of this adaptive complex diffusion filter proved to be beneficial by achieving an increased level of noise reduction while simultaneously better preserving fundamental information. These facts are supported from well known metrics (e.g. MSE-mean squared error, ENL-effective number of looks and CNR-contrast-to-noise ratio) for the synthetic OCT scan and from the assessment made by 3 retina specialist who graded qualitatively the output of the 2D and 3D filters. Conclusions: These findings demonstrate this new formulation and its extension to 3D is beneficial for human analysis of OCT data and suggest it might be an important tool for automated data processing as in segmentation of retinal structures. [1] Bernardes R, Maduro C, Serranho P, Araújo A, Barbeiro S, Cunha-Vaz J. Improved adaptive complex diffusion despeckling filter. OPTICS EXPRESS 18(23):24048-24059, 2010.
- Bioestatística com SPSS: notas de apoioPublication . Serranho, Pedro; Ramos, Maria do RosárioNotas de apoio ao curso de "Biostestatística com SPSS" leccionado pelos Prof. Doutor Francisco Caramelo (Universidade de Coimbra), Prof. Doutora Maria Rosário Ramos e Prof. Doutor Pedro Serranho.
- Characterization of the retinal changes of the 3×Tg-AD mouse model of Alzheimer’s diseasePublication . Ferreira, Hugo; Martins, João; Nunes, Ana; Moreira, Paula I.; Castelo-Branco, Miguel; Ambrósio, António F.; Serranho, Pedro; Bernardes, RuiAlzheimer’s disease (AD) is a progressive neurodegenerative disorder whose diagnosis remains a notable challenge. The literature suggests that cerebral changes precede AD symptoms by over two decades, implying a significantly advanced stage of AD by the time it is usually diagnosed. In the study herein, texture analysis was applied to computed optical coherence tomography ocular fundus images to identify differences between a group of the transgenic mouse model of the Alzheimer’s disease (3×Tg-AD) and a group of wild-type mice, at the ages of one and two-months-old. A substantial difference between groups was found at both time-points across all neuroretina’s layers. Here, the inner nuclear layer stands out both in the level of statistically significant differences and on the extension of these differences which span through the imaged area. Also, the progression of AD is suggested to be spotted by texture analysis as demonstrated by the significant difference found in the inner plexiform and the outer nuclear layers from the age of one to the age of two-months-old. These findings demonstrate the potential of the use of the retina and texture analysis to the diagnosis of AD and monitor AD progression. Besides, the differences between groups found in this study suggest that the 3×Tg-AD model may be inappropriate to study early changes associated with the AD and other animal models should be tested following the same path and rationale. Moreover, these results also suggest that the human genes present in these transgenic mice may have an impact on the neurodevelopment of offspring which would justify the significant changes found at the age of one-month-old.
- Convergence of finite difference schemes for nonlinear complex reaction-diffusion processesPublication . Araújo, Adérito; Barbeiro, Sílvia; Serranho, PedroThis paper is devoted to the proof of the convergence properties of a class of finite difference schemes applied to nonlinear complex reaction-diffusion equations. We investigate the accuracy of the numerical solution considering implicit and semi-implicit discretizations. To illustrate the theoretical results we present some numerical examples computed with a semi-implicit scheme applied to a nonlinear equation.
- Digital ocular fundus imaging: a reviewPublication . Bernardes, Rui; Serranho, Pedro; Lobo, ConceiçãoOcular fundus imaging plays a key role in monitoring the health status of the human eye. Currently, a large number of imaging modalities allow the assessment and/or quantification of ocular changes from a healthy status. This review focuses on the main digital fundus imaging modality, color fundus photography, with a brief overview of complementary techniques, such as fluorescein angiography. While focusing on two-dimensional color fundus photography, the authors address the evolution from nondigital to digital imaging and its impact on diagnosis. They also compare several studies performed along the transitional path of this technology. Retinal image processing and analysis, automated disease detection and identification of the stage of diabetic retinopathy (DR) are addressed as well. The authors emphasize the problems of image segmentation, focusing on the major landmark structures of the ocular fundus: the vascular network, optic disk and the fovea. Several proposed approaches for the automatic detection of signs of disease onset and progression, such as microaneurysms, are surveyed. A thorough comparison is conducted among different studies with regard to the number of eyes/subjects, imaging modality, fundus camera used, field of view and image resolution to identify the large variation in characteristics from one study to another. Similarly, the main features of the proposed classifications and algorithms for the automatic detection of DR are compared, thereby addressing computer-aided diagnosis and computer-aided detection for use in screening programs.
- Huygens’ principle and iterative methods in inverse obstacle scatteringPublication . Ivanyshyn, Olha; Kress, Rainer; Serranho, PedroThe inverse problem we consider in this paper is to determine the shape of an obstacle from the knowledge of the far field pattern for scattering of time-harmonic plane waves. In the case of scattering from a sound-soft obstacle, we will interpret Huygens’ principle as a system of two integral equations, named data and field equation, for the unknown boundary of the scatterer and the induced surface flux, i.e., the unknown normal derivative of the total field on the boundary. Reflecting the ill-posedness of the inverse obstacle scattering problem these integral equations are ill-posed. They are linear with respect to the unknown flux and nonlinear with respect to the unknown boundary and offer, in principle, three immediate possibilities for their iterative solution via linearization and regularization. In addition to presenting new results on injectivity and dense range for the linearized operators, the main purpose of this paper is to establish and illuminate relations between these three solution methods based on Huygens’ principle in inverse obstacle scattering. Furthermore, we will exhibit connections and differences to the traditional regularized Newton type iterations as applied to the boundary to far field map, including alternatives for the implementation of these Newton iterations.
- A hybrid method for inverse scattering for shape and impedancePublication . Serranho, PedroWe present a hybrid method to numerically solve the inverse scattering problem for shape and impedance, given the far-field pattern for one incident direction. This method combines ideas of both iterative and decomposition methods, inheriting the advantages of each of them, such as getting good reconstructions and not needing a forward solver at each step. An optimization problem is presented as the theoretical background of the method and numerical results show its feasibility.
- A hybrid method for inverse scattering for sound-soft obstacles in R3Publication . Serranho, PedroWe present a hybrid method to numerically solve the inverse acoustic soundsoft obstacle scattering problem in R3, given the far-field pattern for one incident direction. This method combines ideas of both iterative and decomposition methods, inheriting advantages of each of them, such as getting good reconstructions and not needing a forward solver at each step. A related Newton method is presented to show convergence of the method and numerical results show its feasibility.
- A hybrid method for sound-hard obstacle reconstructionPublication . Kress, Rainer; Serranho, PedroWe are interested in solving the inverse problem of acoustic wave scattering to reconstruct the position and the shape of sound-hard obstacles from a given incident field and the corresponding far field pattern of the scattered field. The method we suggest is an extension of the hybrid method for the reconstruction of sound-soft cracks as presented in [R. Kress, P. Serranho, A hybrid method for two-dimensional crack reconstruction, Inverse Problems 21 (2005) 773–784] to the case of sound-hard obstacles. The designation of the method is justified by the fact that it can be interpreted as a hybrid between a regularized Newton method applied to a nonlinear operator equation with the operator that maps the unknown boundary onto the solution of the direct scattering problem and a decomposition method in the spirit of the potential method as described in [A. Kirsch, R. Kress, On an integral equation of the first kind in inverse acoustic scattering, in: Cannon, Hornung (Eds.), Inverse Problems, ISNM, vol. 77, 1986, pp. 93–102. Since the method does not require a forward solver for each Newton step its computational costs are reduced. By some numerical examples we illustrate the feasibility of the method.
- A hybrid method for two-dimensional crack reconstructionPublication . Kress, Rainer; Serranho, PedroWe present a new method for solving the time-harmonic inverse scattering problem for sound-soft or perfectly conducting cracks in two dimensions. Our approach extends a method that was recently suggested by one of us for inverse obstacle scattering. It can be viewed as a hybrid between a regularized Newton iterationmethod applied to a nonlinear operator equation involving the operator that, for a fixed incident wave, maps the crack onto the far-field pattern of the scattered wave and a decomposition method due to Kirsch and Kress. As an important feature, in contrast to the traditional Newton iterations for solving inverse scattering problems, our method does not require a forward solver for each iteration step. The theoretical background of the method is based on the minimization of a cost function containing an additional penalty term to deal with reconstructing the full crack. Numerical examples illustrate the feasibility of the method and its stability with respect to noisy data. We expect that the method can also be extended to sound-hard cracks.