Single-scan skeletonization driven by a neighborhood-sequence distance

International audienceShape description is an important step in image analysis. Skeletonization methods are widely used in image analysis as they are a powerful tool to describe a shape. Indeed, a skeleton is a one point wide line centered in the shape which keeps the shape's topology. Commonly, at least two scans of the image are needed for the skeleton computation in the state of art methods of skeletonization. In this work, a single scan is used considering information propagation in order to compute the skeleton. This paper presents also a new single-scan skeletonization using different distances likes d4, d8 and dns

Extraction of bone structure with a single-scan skeletonization driven by distance

International audienceShape description is an important step in image analysis. Skeletonization methods are widely used in image analysis since they are a powerful tool to describe a shape. This paper presents a new single-scan skeletonization using different diskrete distances. The application of this method is the extraction of caracteristics from µCT images in order to estimate the bone state

Path-Based Distance with Varying Weights and Neighborhood Sequences

International audienceThis paper presents a path-based distance where local displacement costs vary both according to the displacement vector and with the travelled distance. The corresponding distance transform algorithm is similar in its form to classical propagation-based algorithms, but the more variable distance increments are either stored in look-up-tables or computed on-the-fly. These distances and distance transform extend neighborhood-sequence distances, chamfer distances and generalized distances based on Minkowski sums. We introduce algorithms to compute, in Z2, a translated version of a neighborhood sequence distance map with a limited number of neighbors, both for periodic and aperiodic sequences. A method to recover the centered distance map from the translated one is also introduced. Overall, the distance transform can be computed with minimal delay, without the need to wait for the whole input image before beginning to provide the result image

Squelettisation en un balayage. Application à la caractérisation osseuse.

Skeletonization is a method for shape recognition and characterization that uses discrete geometry notions. Given a binary image, this method allows the extraction of a skeleton.This skeleton is computed thanks to several scans of the image. It is a centered subset of the shape, thin, topologically equivalent to the input shape and it can be reconstructed. In this thesis we aimed at computing the skeleton with only one scan (streaming mode). We thus proposed a new algorithm that re-organizes the computation on each pixel according to their occurrence order within the image in order to compute an asymmetric distance map and to find the medial axis points. The method does not change the direction of the image information propagation. According to a particular order, which guarantees the same results than those of the reference algorithm results, we can delete the points from the asymmetric distance map while conserving the skeletal points and the medial axis points. Besides, the fact that our skeletons are identical to the pixel to those obtained by the reference method, our algorithm is the fastest. Although our approach is generic, we used this algorithm to develop a software tool for medical imaging applications. Trabecular bones characteristics extraction from 2D binarized images enables bones characterization that matches the observations yielded from other softwareLa squelettisation est une méthode de reconnaissance et de caractérisation des formes utilisant des notions de topologie discrète, qui permet d'extraire le squelette d'une forme binaire. Ce squelette (un sous ensemble de la forme centré, fin, topologiquement équivalent à la forme et reconstructible) se calcule grâce à plusieurs balayages de l'image. Dans ce travail de thèse nous nous sommes intéressé au calcul du squelette en une seule passe (mode " streaming "). Pour cela nous avons proposé un nouvel algorithme qui ré-ordonne les calculs sur chaque pixels dans leur ordre d'apparition dans l'image (sans changer le sens de propagation de l'information dans l'image) en calculant une carte de distance asymétrique puis qui trouve les points de l'axe médian. Selon un ordre particulier, qui garantit l'identité de nos résultats avec ceux d'un algorithme de référence, nous pouvons supprimer les points de la carte de distance en ne conservant que les points du squelette dont les points de l'axe médian. En plus du fait que nos squelettes soient identiques au pixel près à ceux obtenus par l'algorithme de référence, notre algorithme les calcule plus rapidement. Bien que notre approche soit générique, nous avons utilisé cet algorithme pour développer un outil logiciel en imagerie médicale permettant d'extraire les caractéristiques osseuses dans le but de mesurer la structure osseuse à partir du squelette obtenu sur des images de micro-scanner. L'extraction de zones d'os trabéculaire 2D sur des images binarisées, permet bien une caractérisation de l'os en accord avec la vérité terrain obtenue par d'autres logiciels

Minimal-Delay Distance Transform for Neighborhood-Sequence Distances in 2D and 3D

International audienceThis paper presents a path-based distance where local displacement costs vary both according to the displacement vector and with the travelled distance. The corresponding distance transform algorithm is similar in its form to classical propagation-based algorithms, but the more variable distance incre- ments are either stored in look-up-tables or computed on-the-fly. These distances and distance trans- form extend neighborhood-sequence distances, chamfer distances and generalized distances based on Minkowski sums. We introduce algorithms to compute a translated version of a neighborhood sequence distance map both for periodic and aperiodic sequences and a method to derive the centered distance map. A decomposition of the grid neighbors, in ℤ² and ℤ³, allows to significantly decrease the number of displacement vectors needed for the distance transform. Overall, the distance transform can be com- puted with minimal delay, without the need to wait for the whole input image before beginning to provide the result image

A Streaming Distance Transform Algorithm for Neighborhood-Sequence Distances

International audienceWe describe an algorithm that computes a “translated” 2D Neighborhood-Sequence Distance Transform (DT) using a look up table approach. It requires a single raster scan of the input image and produces one line of output for every line of input. The neighborhood sequence is specified either by providing one period of some integer periodic sequence or by providing the rate of appearance of neighborhoods. The full algorithm optionally derives the regular (centered) DT from the “translated” DT, providing the result image on-the-fly, with a minimal delay, before the input image is fully processed. Its efficiency can benefit all applications that use neighborhood- sequence distances, particularly when pipelined processing architectures are involved, or when the size of objects in the source image is limited

Efficient Multicore Implementation of An Advanced Generator of Discrete Chaotic Sequences

International audienceThis paper details the design and implementation performances of an efficient generator of chaotic discrete integer valued sequences. The generator exhibits orbits having very large lengths compared to those given in the literature. It is implemented in C language and parallelized using the Parameterized and Interfaced Synchronous Dataflow Model of Computation (PiSDF MoC). The proposed structure is shown to be scalable, parallel and time efficient. The resulting implementation combines a very long minimal chaotic sequence omin > 7*2^128 32-bit samples and a very high throughput of 173Mbps on 4 cores of a General Purpose Processor

Influence de l'os cortical dans l'appréciation du tissu osseux trabéculaire par radiographies rétro alvéolaires.

Présentation poster dans le cadre des 33emes journées du Collège Nationale des Enseignants en Prothèse OdonthologiqueL'analyse de texture osseuse essaie, à partir d'une radiographie en 2D, de rendre compte de la microarchitecture osseuse en 3D de l'ostrabéculaire. Sur une radiographie rétroalvéolaire, l'os cortical pourrait ainsi créer des interférences plus ou moins importantes selon son niveau de visibilité. Pour certains auteurs, l'oscortical n'a aucune influence sur les trabéculations visibles à la radiographie rétroalvéolaire. Pour d'autres, au contraire, les trabéculations visibles sont une représentation de la surface interne de l'oscortical et pas du tout des trabéculations réelles. Le but de cette étude est de déterminer l'influence de l'os cortical dans l'appréciation du tissu osseux trabéculaire

Evaluation of trabecular bone patterns on dental radiographic images: influence of cortical bone

International audienceFor some authors trabecular bone is highly visible in intraoral radiographs. For other authors, the observed intrabony trabecular pattern is a representation of only the endosteal surface of cortical bone, not of intermedullary striae. The purpose of this preliminary study was to investigate the true anatomical structures that are visible in routine dental radiographs and classically denoted trabecular bone. This is a major point for bone texture analysis on radiographs. Computed radiography (CR) images of dog mandible section in molar region were compared with simulations calculated from high-resolution micro-CT volumes. Calculated simulations were obtained using the Mojette Transform. By digitally editing the CT volume, the simulations were separated into trabecular and cortical components into a region of interest. Different images were compared and correlated, some bone micro-architecture parameters calculated. A high correlation was found between computed radiographs and calculated simulations from micro-CT. The Mojette transform was successful to obtain high quality images. Cortical bone did not contribute to change in a major way simulated images. These first results imply that intrabony trabecular pattern observed on radiographs can not only be a representation of the cortical bone endosteal surface and that trabecular bone is highly visible in intraoral radiographs

Bone texture analysis on dental radiographic images: results with several angulated radiographs on the same region of interest

International audienceBone microarchitecture is the predictor of bone quality or bone disease. It can only be measured on a bone biopsy, which is invasive and not available for all clinical situations. Texture analysis on radiographs is a common way to investigate bone microarchitecture. But relationship between three-dimension histomorphometric parameters and two-dimension texture parameters is not always well known, with poor results. The aim of this study is to performed angulated radiographs of the same region of interest and see if a better relationship between texture analysis on several radiographs and histomorphometric parameters can be developed. Computed radiography images of dog (Beagle) mandible section in molar regions were compared with high-resolution micro-CT (Computed-Tomograph) volumes. Four radiographs with 27° angle (up, down, left, right, using Rinn ring and customized arm positioning system) were performed from initial radiograph position. Bone texture parameters were calculated on all images. Texture parameters were also computed from new images obtained by difference between angulated images. Results of fractal values in different trabecular areas give some caracterisation of bone microarchitecture