Miguel Morgado

Simulation of cellular changes on Optical Coherence Tomography of human retina.

We present a methodology to assess cell level alterations on the human retina responsible for functional changes observable in the Optical Coherence Tomography data in healthy ageing and in disease conditions, in the absence of structural alterations. The methodology is based in a 3D multilayer Monte Carlo computational model of the human retina. The optical properties of each layer are obtained by solving the Maxwells equations for 3D domains representative of small regions of those layers, using a Discontinuous Galerkin Finite Element Method (DG-FEM). Here we present the DG-FEM Maxwell 3D model and its validation against Mies theory for spherical scatterers. We also present an application of our methodology to the assessment of cell level alterations responsible for the OCT data in Diabetic Macular Edema. It was possible to identify which alterations are responsible for the changes observed in the OCT scans of the diseased groups.

Monte Carlo simulation of diabetic macular edema changes on optical coherence tomography data

Optical coherence tomography (OCT) scans were acquired from healthy controls and patients with diabetic macular edema (DME), a common complication of diabetes characterized by increased retinal thickness due to fluid accumulation. The collected OCT data was divided into three distinct groups: healthy subjects, DME patients with significantly increased outer nuclear layer (ONL) thickness and DME patients without visible changes in the ONL. For each group, the ONL was segmented and processed, yielding a representative A-scan. Using reference values for the physical and optical characteristics of the healthy human retina, we used a Monte Carlo method with a model for the ONL to simulate an A-scan for each group and compare it to the real OCT data. This allowed to identify which alterations in the cellular characteristics are responsible for the changes observed in the OCT scans of the diseased groups.

Maxwell's equations based 3D model of light scattering in the retina

The goal of this work is to develop a computational model of the human retina and simulate light scattering through its structure aiming to shed light on data obtained by optical coherence tomography in human retinas. Currently, light propagation in scattering media is often described by Mies solution to Maxwells equations, which only describes the scattering patterns for homogeneous spheres, thus limiting its application for scatterers of more complex shapes. In this work, we propose a discontinuous Galerkin method combined with a low-storage Runge-Kutta method as an accurate and efficient way to numerically solve the time-dependent Maxwells equations. In this work, we report on the validation of the proposed methodology by comparison with Mies solution, a mandatory step before further elaborating the numerical scheme towards the propagation of electromagnetic waves through the human retina.

Digital image acquisition for ophthalmoscope

The aim of this work is to provide a Panoptic™ ophthalmoscope with digital data acquisition. In fact, most ophthalmoscopes used in daily clinical practice do not contain the data recording ability. Therefore, the main advantages of a digital ophthalmoscope are, among others, better quality data sharing, the possibility of exams reassessment and improved medical teaching. Once the challenge was presented by clinical staff working at Coimbra University Hospital, several prototypes technical drawings were idealized in AutoCAD® 2011 environment at Blueworks, and a number of experiments in optics laboratory at Institute of Biomedical Research in Light and Image (IBILI) were accomplished as well. In the end, the prototype developed contains a camera inside and it fits into the ophthalmoscope. In order to verify its capacity to record retinal images and to detect ocular fundus pathologies, the prototype has been clinically tested and its impact in medical community has been markedly positive.

Fluorescence lifetime microscope for corneal metabolic imaging

Assessing corneal metabolism may provide clinicians a tool for diagnosing corneal cells dysfunctions prior to its pathological expression. Flavin adenine dinucleotide (FAD), a metabolic co-factor, exhibits two lifetime components (long and short) upon blue light excitation. Due to that, fluorescence lifetime imaging microscopy (FLIM) may provide a method to evaluate corneal cells metabolism non-invasively. We are developing a single-photon, time-gated fluorescence lifetime microscope for in vivo corneal imaging using structured illumination to improve optical sectioning. Single-photon imaging is provided by a picosecond diode laser with emission at 443nm. Structured illumination is implemented by modulating the laser light through a Digital Micromirror Device (DMD). The fluorescence imaging acquisition is based on an ultrafast time-gated intensified CCD camera operating with gates down to 200ps. We present preliminary data regarding the timing and optical performance of the microscope.

Development of a time-gated fluorescence lifetime microscope for in vivo corneal metabolic imaging

Metabolic imaging can be a valuable tool in the early diagnosis of corneal diseases. Cell metabolic changes can be assessed through non-invasive optical methods due to the autofluorescence of metabolic co-factors nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD). Both molecules exhibit double exponential fluorescence decays, with well-separated short and long lifetime components, which are related to their protein-bound and free states. Corneal metabolism can be monitored by measuring the relative contribution of these two components. Here we report on the development of a fluorescence lifetime imaging microscope for in vivo measurement of FAD fluorescence lifetimes in corneal cells. The microscope is based on one-photon fluorescence excitation, through a pulsed blue diode laser. Fluorescence lifetime imaging is achieved using the Time-Gated technique. Structured illumination is used to improve the low axial resolution of wide-field time-gated FLIM. A Digital Micromirror Device (DMD) is used to produce the sinusoidal patterns required by structural illumination. The DMD control is integrated with the acquisition software of the imaging system which is based on an ultra-high speed gated image intensifier coupled to a CCD camera. We present preliminary results concerning optical and timing performance of the fluorescence lifetime microscope. Preliminary tests with ex-vivo bovine corneas are also described.

Development of an Optical Coherence Tomograph (OCT) for small animal retinal imaging

Optical Coherence Tomography (OCT) is a medical imaging technique mostly used in ophthalmology that has been developed since early 1990s. Based on optical interferometry it is capable of producing high-resolution cross-sectional images of non-homogeneous tissues such as the ocular retina. Our goal is to develop a high speed OCT for retinal imaging in small animals. This will be a fundamental tool for research on retinal physiology and for developing new instrumentation and methods for OCT-based morphological and functional retinal imaging. The overall system is assembled from separated modular blocks to allow performance improvement and easy upgrading. Here, we present the first results obtained with this system.

FLIM as a tool for metabolic imaging of the cornea

We intend to develop an efficient method of measuring respiratory function of the cornea. With this purpose, we resorted to fluorescence lifetime imaging microscopy (FLIM) to monitor the metabolic co-factor flavin adenine dinucleotide (FAD). FAD and nicotinamide adenine dinucleotide (NADH) are co-factors of the electron transport chain. Therefore alterations in amount of these molecules reflect alterations in the metabolism. For assessing the potential of FLIM for metabolic imaging of the cornea, we performed a series of experiments using a time-correlated single photon counting (TCSPC) fluorescence lifetime microscope (Picoquant to MicroTime 100 coupled to an Olympus BX51 Microscope). In this technique, the acquired signal is the convolution between the instrument response function (IRF) and the fluorescence signal from the sample. IRF was acquired using an Erythrosin B solution. In this work we show that it is possible to acquire fluorescence lifetime images of rat and bovine corneas using FAD autofluorescence.

neuroCornea — Diabetic peripheral neuropathy early diagnosis and follow-up through in vivo automatic analysis of corneal nerves morphology

Peripheral diabetic neuropathy is the major cause of chronic disability in diabetic patients. The early diagnosis and accurate assessment of peripheral neuropathy are important to define the higher risk patients, decrease patient morbidity and assess the performance of new therapies. However, the peripheral neuropathy diagnosis often fails or occurs only when patients became symptomatic due to the non-availability of a simple non invasive method for early diagnosis. Corneal confocal microscopy is a non-invasive imaging modality that can document corneal nerves morphology. In this project, we will develop a technique for early diagnosis of diabetic neuropathy based on automatic analysis of corneal nerves images. This project comprises the development of automatic algorithms for nerve segmentation and morphometric parameters extraction, the evaluation of the best parameters for early diagnosis and follow-up of diabetic neuropathy and the development of a corneal confocal imaging module to be used as an add-on to a standard slit-lamp.