Accurate and reliable segmentation of the optic disc in digital fundus images

We describe a complete pipeline for the detection and accurate automatic segmentation of the optic disc in digital fundus images. This procedure provides separation of vascular information and accurate inpainting of vessel-removed images, symmetry-based optic disc localization, and fitting of incrementally complex contour models at increasing resolutions using information related to inpainted images and vessel masks. Validation experiments, performed on a large dataset of images of healthy and pathological eyes, annotated by experts and partially graded with a quality label, demonstrate the good performances of the proposed approach. The method is able to detect the optic disc and trace its contours better than the other systems presented in the literature and tested on the same data. The average error in the obtained contour masks is reasonably close to the interoperator errors and suitable for practical applications. The optic disc segmentation pipeline is currently integrated in a complete software suite for the semiautomatic quantification of retinal vessel properties from fundus camera images (VAMPIRE)

Optic Disk Segmentation Using Histogram Analysis

In the field of disease diagnosis with ophthalmic aids, automatic segmentation of the retinal optic disc is required. The main challenge in OD segmentation is to determine the exact location of the OD and remove noise in the retinal image. This paper proposes a method for automatic optical disc segmentation on color retinal fundus images using histogram analysis. Based on the properties of the optical disk, where the optical disk tends to occupy a high intensity. This method has been applied to the Digital Retinal Database for Vessel Extraction (DRIVE)and MESSIDOR database. The experimental results show that the proposed automatic optical segmentation method has an accuracy of 55% for DRIVE dataset and 89% for MESSIDOR databas

Quantum-limited estimation of the axial separation of two incoherent point sources

Improving axial resolution is crucial for three-dimensional optical imaging systems. Here we present a scheme of axial superresolution for two incoherent point sources based on spatial mode demultiplexing. A radial mode sorter is used to losslessly decompose the optical fields into a radial mode basis set to extract the phase information associated with the axial positions of the point sources. We show theoretically and experimentally that, in the limit of a zero axial separation, our scheme allows for reaching the quantum Cram\'er-Rao lower bound and thus can be considered as one of the optimal measurement methods. Unlike other superresolution schemes, this scheme does not require neither activation of fluorophores nor sophisticated stabilization control. Moreover, it is applicable to the localization of a single point source in the axial direction. Our demonstration can be useful to a variety of applications such as far-field fluorescence microscopy.Comment: Comments are welcom

Automated retinal analysis

Diabetes is a chronic disease affecting over 2% of the population in the UK [1]. Long-term complications of diabetes can affect many different systems of the body including the retina of the eye. In the retina, diabetes can lead to a disease called diabetic retinopathy, one of the leading causes of blindness in the working population of industrialised countries. The risk of visual loss from diabetic retinopathy can be reduced if treatment is given at the onset of sight-threatening retinopathy. To detect early indicators of the disease, the UK National Screening Committee have recommended that diabetic patients should receive annual screening by digital colour fundal photography [2]. Manually grading retinal images is a subjective and costly process requiring highly skilled staff. This thesis describes an automated diagnostic system based oil image processing and neural network techniques, which analyses digital fundus images so that early signs of sight threatening retinopathy can be identified. Within retinal analysis this research has concentrated on the development of four algorithms: optic nerve head segmentation, lesion segmentation, image quality assessment and vessel width measurements. This research amalgamated these four algorithms with two existing techniques to form an integrated diagnostic system. The diagnostic system when used as a 'pre-filtering' tool successfully reduced the number of images requiring human grading by 74.3%: this was achieved by identifying and excluding images without sight threatening maculopathy from manual screening

Electro-optic photonic circuits from linear and nonlinear waves in nanodisordered photorefractive ferroelectrics

The work presented in this thesis addresses different aspects of three main physical issue belonging to the eld of nonlinear optics, quantum optics and optical microscopy. We analyze how photorefraction can be used to photoinduced a tapered ber index of refraction patterns in the bulk of nano-disordered crystals, and we observe how these patterns are able to modulate the phase of Gaussian beams converting them to Bessel-Gauss beams, enhancing their depth of eld and their ability to self-heal after an obstacle. These properties suggest the use of Bessel beam in microscopy. In our investigations we proposed and experimentally demonstrated, in turbid media, the idea of using the interference between multiple Bessel beams to generate a light field that is non diffracting, self-healing, but also localized along the propagation axis. Our study on superimposed Bessel beams reveals how the interference between their side lobes has the overall effect of reducing the amount of energy possessed by the beam outer structures, practically enhancing their localization in the radial direction as well as in the axial. At present we are studying how to implement these findings in a light sheet microscope to improve optical sectioning. Also described in this thesis are a number of intriguing experiments carried out on disordered ferroelectrics and their giant response, these including negative intrinsic mass dynamics, ferroelectric supercrystals, rogue wave dynamics driven by enhanced disorder and first evidence of spatial optical turbulence. Lastly, relying on the necessarily reversible nature of the microscopic process, we demonstrate how a single photon is not able to entangle two distant atoms because of conservation laws, clarifying the long standing debate on the nature of single-photon nonlocality and introducing fundamental limitation, in the use of linear optics for quantum technology

Coherent phonons in plasmonic nanostructures and surface phonon polariton resonators for enhanced light-matter interaction in the mid-IR

Light exhibits a rich set of phenomena when interacting with matter, making it an invaluable tool for fundamental research and also for technological applications. However, in many instances, the size mismatch between matter components and the localization of light with conventional optical elements hampers a more fruitful exploitation of this interaction. The excitation of plasmon polaritons in metals enables us to circumvent the limits in the light localization imposed by far-field diffraction. Nevertheless, the light confinement at optical frequencies in plasmonic systems requires the storage of energy in the motion of free-electrons, which are subject to unavoidable ohmic losses. At lower frequencies, the large negative real permittivity of metals leads to a poor confinement of the near-field radiation. The high losses impede the application of plasmonic systems in the transmission and the guiding of sub-diffraction optical modes. Additionally, the poor confinement at longer wavelengths limits the study and the application of enhanced molecular sensing which requires spatial and spectral overlap between confined modes and vibrational transitions in chemical species. Thus, the search for alternative materials that can provide sub-diffraction light confinement with low losses across the electromagnetic spectrum becomes a major goal in nanophotonics research. In this thesis we explore how the fast electronic relaxation processes related to losses in plasmonic systems can be used to generate coherent acoustic phonons of tailored frequency and amplitude in metallic nanoantennas subject to dielectric mechanical constraints. The damping of coherent phonons through emission of surface acoustic waves (SAWs) is also explored, where narrow-frequency mechanical modulation of plasmonic resonances via the emitted SAWs is shown possible. Finally, we investigate the potential of sub-diffraction surface phonon polariton resonances in polar dielectric materials as an alternative to plasmonic systems for sensing in the mid-infrared range, where the detection of sub-nanometric film thicknesses is achieved.Open Acces