Alfonso Gastelum

The Ngongotaha river UDPS experiment: low-cost underwater dynamic stereo photogrammetry

We propose to integrate the newest developments in stereomatching theory, affordable parallel processing capabilities (using GPU e.g. PC gaming/graphic card) and statistical surface analysis to implement and test an in-situ Underwater Dynamic Stereo Photogrammetry (UDSP) system for civil engineering applications. The proposed UDPS system aims to provide underwater Digital Elevation Models (DEM), for applications such as a two-dimensional discrete matrix of data underwater elevations. Experiments on river bed stereophotogrammetry in the Ngongotaha Stream near Rotorua using consumer grade stereo cameras including Go-Pro and Fujifilm W3 are used in through-water and underwater calibration and stereo measurements of 32 pebbles on the river bed. Pebbles are measured and identified. Initial results highlight the need for specialised equipment for through-water and underwater photogrammetry experiments to limit blurring effects caused by the water-plastic-air interfaces. Despite poor optical quality of the images obtained, we were able to correlate pebble sizes from calibrated stereo depth maps and actual measurement.

Texture Analysis of Contrast-Enhanced Digital Mammography CEDM Images

A texture analysis aimed at finding correlations between textural descriptors and lesion diagnosis was applied to Contrast-Enhanced Digital Mammography CEDM subtracted images acquired under single-energy temporal subtraction modality using iodine-based contrast medium. The study, based on textural descriptors from Gray Level Co-occurrence Matrix GLCM, included 68 CEDM images of 17 patients, 10 cancer and 7 benign, acquired 1 to 5i¾?min after iodine injection. Seventeen GLCM descriptors were analyzed. Image processing consisted of geometric registration, logarithmic subtraction, and selection of regions-of-interest adipose, glandular and lesion ROIs by the radiologist. Results for lesion ROIs showed that homogeneity, normalized homogeneity, second-order inverse moment, energy and inverse variance were insensitive to the presence of iodine; a linear correlation existed between the sum mean and mean pixel value. Logistic regression showed that a linear combination of entropy and diagonal momentum discriminated between malignant and benign lesions with 79i¾?% specificity, 93i¾?% sensitivity and 87i¾?% accuracy.

Construction of a Model of the Upper Gastrointestinal System for the Simulation of Gastroesophagoendoscopic Procedures

We describe current work on the construction of three‐dimensional anatomical models of the upper gastrointestinal system, its computer navigation using a virtual endoscope, and the modeling of physical interactions of the model and the endoscope, including lens distortions and illumination conditions as well as collisions. This model will be part of a computer‐simulation system for the training of gastroendoscopic procedures.

Building a three-dimensional model of the upper gastrointestinal tract for computer simulations of swallowing

We aimed to provide realistic three-dimensional (3D) models to be used in numerical simulations of peristaltic flow in patients exhibiting difficulty in swallowing, also known as dysphagia. To this end, a 3D model of the upper gastrointestinal tract was built from the color cryosection images of the Visible Human Project dataset. Regional color heterogeneities were corrected by centering local histograms of the image difference between slices. A voxel-based model was generated by stacking contours from the color images. A triangle mesh was built, smoothed and simplified. Visualization tools were developed for browsing the model at different stages and for virtual endoscopy navigation. As result, a computer model of the esophagus and the stomach was obtained, mainly for modeling swallowing disorders. A central-axis curve was also obtained for virtual navigation and to replicate conditions relevant to swallowing disorders modeling. We show renderings of the model and discuss its use for simulating swallowing as a function of bolus rheological properties. The information obtained from simulation studies with our model could be useful for physicians in selecting the correct nutritional emulsions for patients with dysphagia.

Computational tools for extracting, representing and analyzing facial features

In this work we present the development of a software for intuitive and interactive extraction of 3D landmarks on triangular meshes, by employing techniques of scientific visualization, interactive picking, and haptic feedback. The software was employed as a tool for analyzing facial features, over a database of 35 face models from Mexican healthy subjects, acquired with a low cost structured light stereovision system. We aimed to obtain the statistical variation of a set of 19 craniofacial points, representing facial features, along the population under study, in order to determine the representative features, and modes of variation, via Principal Components Analysis. As a result, the mean face shape was approximated, by using interactive cage-based deformable registration. As for interactive picking and haptic feedback, we implemented geometrical algorithms based on an octree representation, for achieving accurate real time collision detection.

Comparative morphometry of facial surface models obtained from a stereo vision system in a healthy population

Our goal is to obtain three-dimensional measurements of craniofacial morphology in a healthy population, using standard landmarks established by a physical-anthropology specialist and picked from computer reconstructions of the face of each subject. To do this, we designed a multi-stereo vision system that will be used to create a data base of human faces surfaces from a healthy population, for eventual applications in medicine, forensic sciences and anthropology. The acquisition process consists of obtaining the depth map information from three points of views, each depth map is obtained from a calibrated pair of cameras. The depth maps are used to build a complete, frontal, triangular-surface representation of the subject face. The triangular surface is used to locate the landmarks and the measurements are analyzed with a MATLAB script. The classification of the subjects was done with the aid of a specialist anthropologist that defines specific subject indices, according to the lengths, areas, ratios, e...

Visualising 3D porous media fluid interaction using X-ray CT data and Smooth Particles Hydrodynamics modelling

We propose the use of the Lagrangian method Smoothed particle Hydrodynamics (SPH) to model the behaviour of fluids through a pore structure of a volcanic soil core sample. Such studies are of importance to simulate preferential flows which are essential in the leeching of organic and chemical compounds in underground aquifers. Our approach combines X-ray Computed Tomography imaging, and image processing techniques to extract the 3D porous structure of the media studied. Smoothed particle Hydrodynamics modelling simulates water transport in the reconstructed 3D pore network using Navier Stokes governing laws. An isolated pore was considered as a case-based study. We are currently extending our simulation to a full sized pore network.

A mesh-free mechanical model of the upper gastrointestinal system

Realistic behavior in Computer Simulation of biological system (e.g. humans organs) is essential to 3D modeling in medicine. In order to improve realistic responses of 3D organ model it is essential to use mechanical models that can deal with multiple objects internal and external interactions in a reasonable time frame. We will apply the Smooth Particles Hydrodynamics (SPH) to model the esophagus and the stomach, thus constructing a physical background for interaction. We used a multilayer model of particles related to a single triangle mesh. Each particle layers represent distinct biological tissues of the esophagus and the stomach.

Automatic 3D lip shape segmentation and modelling

The correct representation of the 3D lipspsila movement has been receiving growing interest in different industries. We present a new user-specific 3D mechanical lips model. Static 3D face measurements are obtained from readily available acquisition devices (either a 3D scanner or an active illumination stereo rig). The lip contours are extracted from the face surface using our recently proposed algorithm for segmentation 3D surfaces using active contours. The algorithm allows to obtain different lip surfaces that can be used as input data for the 3D mechanical model. The 3D lips are modeled as a set of particles whose dynamic behaviour is governed by the Smooth Particles Hydrodynamics (SPH). Finally, a force field derived from ellipsoid muscle encircling the lips simulates the muscles controlling the lips motion. Experiments confirmed good potentialities of the proposed approach.

Navigation and Interaction with the Model of the Upper Gastrointestinal System

We report advancements on navigation and simulated interaction with a model of the esophagus and stomach, reported in previous works. Computer training in endoscopic procedures allows the specialist to interact with a virtual model and provides him different points of view of the anatomical area of interest. Such enriched navigation permits to the specialist to have a better understanding of the volume. An important improvement was the inclusion of abnormal anatomy, from two types, the first one is related to the color features of the disease, so we added the possibility to change the color assigned to a group of vertices from a triangle vicinity. The second one is a direct modification in the triangle structure, in order to simulate blisters and injures in the model. The optical distortion of the endoscope was also simulated in the navigator allowing the user a quantitative assessment of distortion when he measures an injury. Another improvement of the model consisted in a radial‐collapsed representation of the esophagus, which is its natural state. To this collapsed state we superposed the interaction of the triangle mesh with a model of the air pressure against the walls. The collapsed wall of the mesh gives us the opportunity to train the user in the insertion of the endoscope.