Louis Legrand
University of Burgundy
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Featured researches published by Louis Legrand.
Investigative Radiology | 1999
Alain Lalande; Louis Legrand; Paul Walker; F. Guy; Y. Cottin; Sophie Roy; François Brunotte
RATIONALE AND OBJECTIVES Gated cardiac cine magnetic resonance imaging provides accurate dynamic data of the left ventricular function. However, the manual extraction of important physiologic parameters such as myocardium wall thickness and left ventricular volumes is invariably time consuming and subjective. To reduce the variability and time constraints inherent in observer contour tracing, the authors developed an automatic left ventricle contour-detection method. METHODS The purpose was to apply fuzzy logic-based automatic contour detection to identification of endocardial and epicardial borders in short-axis magnetic resonance images. The automatic contouring was compared with manual tracing using the calculated ejection fraction as the comparison criterion. RESULTS A good correlation was found between the two approaches (r2 = 0.98). CONCLUSIONS The ejection fraction can be obtained using this automatic contouring method.
European Radiology | 2004
Alexandre Comte; Alain Lalande; Paul Walker; Alexandre Cochet; Louis Legrand; Yves Cottin; Jean-Eric Wolf; François Brunotte
MRI with paramagnetic contrast agent allows the assessment of the extent of myocardial tissue injury after infarction. Visual segmental scoring has been widely used to define the transmural extent of myocardial infarction, but no attempt has been made to use visual scores in order to assess the percentage of the whole myocardium infarcted. By summing all the segmental scores using a 17-segment model, a global index of the size of the infarcted myocardium is easily obtained. The entire left ventricle of 60 patients with a recent myocardial infarction was scanned using an ECG-gated gradient echo sequence after injection of gadolinium contrast agent. The global score was defined as the sum of the scores on each segment, and expressed as a percentage of the maximum possible score. This index was compared with a planimetric evaluation of hyperenhancement, expressed as a percentage of the left ventricle myocardial volume. There is a good correlation between the two methods (r=0.91; y=1.06x+0.20), and the Bland-Altman plot shows a high concordance between the two approaches (mean of the differences =1.45%). A visual approach based on a 17-segment model can be used to evaluate the global myocardial extent of the hyperenhancement with similar results to planimetry.
international conference of the ieee engineering in medicine and biology society | 2001
Franck Marzani; Elodie F. Calais; Louis Legrand
Describes an approach allowing the analysis of human motion in 3D space. The system that we developed is composed of three CCD (charge-coupled device) cameras that capture synchronized image sequences of a human body in motion without the use of markers. Characteristic points belonging to the boundaries of the body in motion are first extracted from the initial images. 2D superquadrics are then adjusted on these points by a fuzzy clustering process. After that, the position of a 3D model based on a set of articulated superquadrics, each of them describing a part of the human body, is reconstructed. An optical flow process allows the prediction of the position of the model from its position at a previous time, and gives initial values for the fuzzy classification. The results that we present more specifically concern the analysis of movement disabilities of a human leg during gait. They are improved by using articulation-based constraints. The methodology can be used in human motion analysis for clinical applications.
international conference of the ieee engineering in medicine and biology society | 2012
Marie Xavier; Alain Lalande; Paul Walker; François Brunotte; Louis Legrand
This paper presents a method for local myocardial motion estimation from a conventional steady-state free precession cine-MRI sequence using a modified phase-based optical flow (OF) technique. Initially, the technique was tested on synthetic images to evaluate its robustness with regards to Rician noise and to brightness variations. The method was then applied to cardiac images acquired on 11 healthy subjects. Myocardial velocity is measured in centimeter per second in each studied pixel and visualized as colored vectors superimposed on MRI images. The estimated phase-based OF results were compared with a reference OF method and gave similar results on synthetic images, i.e., without a significant difference of the mean angular error. Applied on cine-MRI of normal hearts, the calculated velocities from short-axis images concord with values obtained in the literature. The advantage of the presented method is its robustness with respect to Rician noise and to brightness changes often observed in cine-MRI sequences, and especially with the through-plane movement of the heart. Motion assessment using our method on cine-MR images gives promising results on motion estimation on a pixel-by-pixel basis, leading to a regional measurement of the time-velocity course of myocardial displacement in different segments of the heart wall.
Investigative Radiology | 2002
Alain Lalande; Philippe Khau Van Kien; Nicolas Salve; Dourïed Ben Salem; Louis Legrand; Paul Walker; Jean-Eric Wolf; François Brunotte
Lalande A, Khau van Kien P, Salvé N, et al. Automatic determination of aortic compliance with cine-magnetic resonance imaging: An application of fuzzy logic theory. Invest Radiol 2002;37:685–691. Rationale and Objectives. Aortic compliance is defined as the relative change in aortic cross-sectional area divided by the change in arterial pressure. Magnetic resonance imaging (MRI) is a useful imaging modality for the noninvasive evaluation of aortic compliance. However, manual tracing of the aortic contour is subject to important interobserver variations. To estimate the aortic compliance from cine-MRI, a method based on fuzzy logic theory was elaborated. Materials and Methods.Seven healthy volunteers and eight patients with Marfan syndrome were examined using an ECG gated cine-MRI sequence. The aorta was imaged in the transverse plane at the level of the pulmonary trunk. A method based on fuzzy logic was developed to automatically detect the aortic contour. Results. Through our robust automatic contouring method, the calculation of aortic cross-sectional areas allows an estimation of the aortic compliance. Conclusion. The aortic compliance can be obtained from a fuzzy logic based automatic contouring method, thereby avoiding the important interobserver variation often associated with manual tracing.
Journal of Magnetic Resonance Imaging | 2008
Alain Lalande; P. Khau Van Kien; Paul Walker; L. Zhu; Louis Legrand; Mireille Claustres; X. Jeunemaître; François Brunotte; Jean-Eric Wolf
To evaluate aortic elasticity with MRI on young asymptomatic individuals with mutation of the smooth muscle myosin heavy chain in whom aortic enlargement is not present.
Journal of Cardiovascular Magnetic Resonance | 2004
Alain Lalande; Nicolas Salve; Alexandre Comte; Marie-Christine Jaulent; Louis Legrand; Paul Walker; Yves Cottin; Jean-Eric Wolf; François Brunotte
The calculation of the left ventricular ejection fraction (LVEF) is dependent upon the accurate measurement of diastolic and systolic left ventricular volumes. Although breath-hold cine magnetic resonance imaging (MRI) allows coverage of the whole cardiac cycle with an excellent time resolution, many authors rely on the visual selection of diastolic and the systolic short-axis slices in order to reduce the postprocessing time. An automatic method was developed to detect the endocardial contour on each image, allowing an automatic selection of the systolic frame. The calculated ejection fraction was compared with radionuclide ventriculography (RNV). Sixty-five patients were examined using an electrocardiogram (ECG)-gated gradient echo sequence. Among these examinations, manual and automatic processing with MRI were compared when the time of the systolic frame concorded. Good correlations have been found between the automatic MRI approach and RNV, and between manual and automatic processing on MRI alone. The results show that the automatic determination of the ejection fraction is feasible, and should constitute an important step toward a larger acceptance of MRI as a routine tool in heart disease imaging. One major benefit of using automatic postprocessing is that it may eliminate the visual choice of the systolic frame, inaccurate in more than 50% of the studied patients.
Archive | 2008
Ernesto Damiani; Albert Dipanda; Kokou Yetongnon; Louis Legrand; P. Schelkens; Richard Chbeir
Traditionally, signal processing techniques lay at the foundation of multimedia data processing and analysis. In the past few years, a new wave of advanced signal-processing techniques has delivered exciting results, increasing systems capabilities of efficiently exchanging image data and extracting useful knowledge. Signal Processing for Image Enhancement and Multimedia Processing is written by global experts who have extended the best papers presented at the SITIS 2006 International Conference to chapter versions. This edited book presents research results on the application of advanced signal processing techniques for improving the value of image and video data. In addition, this volume includes discussions on feature-based techniques for deep, feature-oriented analysis of images, plus new results on video coding on the time-honored topic of securing image information. Signal Processing for Image Enhancement and Multimedia Processing is designed for a professional audience of practitioners and researchers in industry. It is also suitable as a reference or secondary text for advanced-level students in computer science and engineering.
Journal of Electronic Imaging | 2002
Elodie F. Calais; Louis Legrand; Yvon Voisin; Alain Diou
This paper presents a novel approach to human gait analysis using a marker-free system. The devised acquisition system is composed of three synchronized and calibrated charge coupled device cameras. The aim of this work is to recognize in gray level image sequences the leg of a walking human and to reconstruct it in the three-dimensional space. An articulated threedimensional (3D) model of the human body, based on the use of tapered superquadric curves, is first introduced. A motion-based segmentation, using morphological operators, is then applied to the image sequences in order to extract the boundaries of the leg in motion. A reconstruction process, based on the use of a least median of squares regression is next performed, to determine the location of the human body in the 3D space. Finally, a spatial coherence is imposed on the reconstructed curves in order to better fit the anatomy of the leg and to take into account the articulated model. Each stage of the proposed methodology has been tested both on synthetic images and on real world images of walking humans. The obtained results suggest that this approach is quite promising and should be useful in the study of the gait.
computer-based medical systems | 1996
Franck Marzani; Louis Legrand; Liliane Dusserre
This paper deals with a new constraint for determining optical flow fields. This constraint is called the Fourier adaptive smoothness. It can be seen as an improvement of some existing differential techniques. It includes the magnitude image of an extended temporal Fourier transform in the smoothness constraint of the equation used for calculating the flow field. In fact a temporal window of a few frames is displaced along the sequence in order to calculate the one-dimensional corresponding Fourier transform. The resulting local magnitude image allows to constrain the smoothness of the displacement field. The authors compare on angiographic images this approach with two other well known optical flow methods wing differential techniques. A criterion is defined to allow a quantitative analysis of the results. Qualitative remarks are also given. The authors show that the constraint introduced in this paper brings better results in most cases than the two others in addition to its processing speed.