Showing papers by "Francoise Preteux published in 1996"

Process for the reconstruction of a 3D image with contrast and resolution improvements and application of said process to the production of an attentuation cartography of an object

Abstract: A three-dimensional image of an object is constructed by a process using values assumed by a property of the object in an array of elementary volumes of the object The process determines the measured projections of the property and reconstructs the three-dimensional image of the object by iteration The iteration includes steps of carrying out a reconstruction of a first three dimensional image of the object, estimating local parameters defining an anisotropic model of the object as a function of the reconstructed three-dimensional image, deducing calculated projections of the property passing through at least one elementary volume, comparing at least one calculated projection with the measured projection in order to deduce therefrom a projection difference, determining a weighting factor, and performing an updating of each elementary volume

Three-dimensional reconstruction from incomplete Fourier spectra: an extrapolation approach

Abstract: 3D reconstruction from an incomplete data set is an ill- posed problem. To overcome this drawback, an approach based on constrained optimization is introduced. This approach provides a powerful mathematical framework for selecting a specific solution from the set of feasible solutions; this is done by minimizing some criteria depending on prior densitometric information. We propose a global optimization scheme using a deterministic relaxation algorithm based on Bregman's algorithm associated with half-quadratic minimization techniques. When used for 3D vascular reconstruction from 2D digital subtracted angiography data, such an approach allows reconstructing well-contrasted 3D vascular network in comparison with results obtained by using standard algorithms.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Mobile wavelet method: application to active contour modeling and surface reconstruction

Abstract: Deterministic hierarchical approaches in image analysis comprise two major sub-classes: the multiresolution approach and the scale-space representation. Both approaches require either a coarse-to-fine exploration of the hierarchical structure, or a careful selection of a single analysis parameter, but neither one takes full advantage of the hierarchical structure (the end result is obtained at only one analysis level). To overcome this limitation, we propose an explicit hierarchical-based model in which any image primitive is expressed as a finite sum of mobile wavelets (MW), which are defined as wavelets whose dilation, translation and amplitude parameters are allowed to vary. This description derives from an adaptive discretization of the continuous, inverse wavelet transform. First, the MW-based representation is used within the framework of active contour modeling. The primitive corresponds to a deformable, parametrized curve expressed as a sum of MWs. The initial curve is refined by updating the three parameters of each MW in order to minimize the intensity gradient along the active contour. Surface reconstruction is also addressed by the MW approach. In this case, the primitive, the intensity function, is expressed as a sum of MW whose associated parameters are estimated from the noisy data by minimizing a regularizing energy functional.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Method for reconstructing a 3d image with enhanced contrast and resolution

Abstract: A method for reconstructing a three-dimensional image of an object (I3D) defined by values taken by a property of the object (1) in a network of voxels of the three-dimensional image of the object, wherein measured projections (PM) of the property are determined, and the three-dimensional image of the object is iteratively reconstructed by (a) reconstructing a first three-dimensional image of the object; (b) estimating local parameters defining an anisotropic model (ML) of the object according to the reconstructed three-dimensional image; (c) deducing calculated projections (PC) of the object through at least one voxel; (d) comparing (E1) at least one calculated projection (PC) with the measured projection (PM) to deduce a projection difference; (e) determining a weight coefficient; (f) updating (E2) each voxel; and (g) repeating at least steps (c) through (f). The method is useful for medical imaging.

Procede de reconstruction d'une image 3d avec amelioration du contraste et de la resolution

Abstract: L'invention concerne un procede de reconstruction d'une image tridimensionnelle d'un objet (I3D), definie par des valeurs prises par une propriete de l'objet (1) en un reseau de volumes elementaires de l'image tridimensionnelle de l'objet, consistant: a determiner des projections mesurees (PM) de la propriete; a reconstruire l'image 3D de l'objet par iteration: a) effectuer une reconstruction d'une premiere image 3D de l'objet; b) estimer des parametres locaux definissant un modele anistrope (ML) de l'objet en fonction de l'image 3D reconstruite; c) a deduire des projections calculees (PC) de la propriete passant par au moins un volume elementaire; d) comparer (E1) au moins une projection calculee avec la projection mesuree pour en deduire une difference de projection; e) determiner un coefficient de poids; f) effectuer une mise a jour (E2) de chaque volume elementaire; g) reiterer au moins les etapes c) a f) Application a l'imagerie medicale