Claudia Chevrefils - Academia.edu (original) (raw)

Uploads

Papers by Claudia Chevrefils

Osteoporosis International, 1996

Avancement en élastographie -- Théorie sur l'image de déformation et la résolution du PD -- C... more Avancement en élastographie -- Théorie sur l'image de déformation et la résolution du PD -- Construction d'un élastogramme à partir de données ultrasonores -- Construction d'un élastogramme à partir de données simulées -- Modèles analytiques -- L'efficacité de transfert de contraste -- Théorie sur la résolution du PI en élastographie -- Les méthodes d'optimisation -- Calcul de la matrice de sensibilité -- Élimination des modules négatifs -- Résumé de l'algorithme de résolution du problème inverse -- Effet d'une incertitude sur les conditions aux frontières dans la résolution du problème inverse -- Effets des conditions aux frontières de quasi-glissement et de quasi-orthogonalité sur les images de déformation et de rigidité -- Effet de la résolution hybride sur les images de rigidité du PI -- Effet de la position de l'inclusion dans un cas de résolution hybride de glissement partiel -- Effet de différents degrés d'erreurs sur les conditions aux fro...

IEEE Transactions on Information Technology in Biomedicine, 2009

This paper presents a unified framework for automatic segmentation of intervertebral disks of sco... more This paper presents a unified framework for automatic segmentation of intervertebral disks of scoliotic spines from different types of magnetic resonance (MR) image sequences. The method exploits a combination of statistical and spectral texture features to discriminate closed regions representing intervertebral disks from background in MR images of the spine. Specific texture features are evaluated for three types of MR sequences acquired in the sagittal plane: 2-D spin echo, 3-D multiecho data image combination, and 3-D fast imaging with steady state precession. A total of 22 texture features (18 statistical and 4 spectral) are extracted from every closed region obtained from an automatic segmentation procedure based on the watershed approach. The feature selection step based on principal component analysis and clustering process permit to decide among all the extracted features which ones resulted in the highest rate of good classification. The proposed method is validated using a supervised k-nearestneighbor classifier on 505 MR images coming from three different scoliotic patients and three different MR acquisition protocols. Results suggest that the selected texture features and classification can contribute to solve the problem of oversegmentation inherent to existing automatic segmentation methods by successfully discriminating intervertebral disks from the background on MRI of scoliotic spines.

Spine, 2008

Study Design. Proof of concept of a spine surgery simulator (S3) for the assessment of scoliosis ... more Study Design. Proof of concept of a spine surgery simulator (S3) for the assessment of scoliosis instrumentation configuration strategies. Objective. To develop and assess a surgeon-friendly spine surgery simulator that predicts the correction of a scoliotic spine as a function of the patient characteristics and instrumentation variables. Summary of Background Data. There is currently no clinical tool sufficiently user-friendly, reliable and refined for the preoperative planning and prediction of correction using different instrumentation configurations. Methods. A kinetic model using flexible mechanisms has been developed to represent patient-specific spine geometry and flexibility, and to simulate individual substeps of correction with an instrumentation system. The surgeon-friendly simulator interface allows interactive specification of the instrumentation components, surgical correction maneuvers and display of simulation results. Results. The simulations of spinal instrumentation procedures of 10 scoliotic cases agreed well with postoperative results and the expected behavior of the instrumented spine (average Cobb angle differences of 3.5°to 4.6°in the frontal plane and of 3.6°to 4.7°in the sagittal plane). Forces generated at the implant-vertebra link were mostly below reported pull-out values, with more important values at the extremities of the instrumentation. Conclusion. The spine surgery simulator S3 has proven its technical feasibility and clinical relevance to assist in the preoperative planning of instrumentation strategies for the correction of scoliotic deformities.

Abstract. A robust method to segment intervertebral disks and spinal canal in magnetic resonance ... more Abstract. A robust method to segment intervertebral disks and spinal canal in magnetic resonance images is required as part of a precise 3D reconstruction for computer assistance during diskectomy procedure with minimally invasive surgery approach. In this paper, an unsupervised segmentation technique for intervertebral disks and spinal canal from MRI data is presented. The proposed scheme uses a watershed transform and morphological operations to locate regions containing structures of interest. Results show that the method is robust enough to cope with variability of shapes and topologies characterizing MRI images of scoliotic patients. 1

In this paper, a vessel segmentation method from hyperspectral retinal images based on the Multi-... more In this paper, a vessel segmentation method from hyperspectral retinal images based on the Multi-Scale Line Detection algorithm is proposed. The method consists in combining segmentation information from several consecutive images obtained at specific wavelengths around the green channel to produce an accurate segmentation of the retinal vessel network. Images obtained from six subjects were used to evaluate the performance of the proposed method. Preliminary results suggest a potential advantage of combining multispectral information instead of using only the green channel in segmenting retinal blood vessels.

Alzheimer's & Dementia, 2020

Translating recent advances in the diagnosis of Alzheimer’s disease (AD) and other dementias to c... more Translating recent advances in the diagnosis of Alzheimer’s disease (AD) and other dementias to clinical practice using biomarker‐based approaches requires accessible, affordable biomarkers. This protocol tested the performance of a Retinal Deep Phenotyping platform for the detection of likely positron‐emission tomography (PET) amyloid status (negative or positive) in human subjects. This platform generates data rich retinal reflectance images captured non‐invasively with a Metabolic Hyperspectral Retinal Camera (MHRC) yielding specific spatial‐spectral features which are analyzed by a machine learning algorithm relatively to a recognized gold standard biomarker (in this case PET amyloid imaging).

RESUME: Lors de discectomie par thoracoscopie, les outils de visualisation procurent peu d’inform... more RESUME: Lors de discectomie par thoracoscopie, les outils de visualisation procurent peu d’information de profondeur et le champ de visualisation de la camera miniature inseree dans le patient est relativement restreint. Aussi, le mouvement simultane de la camera et des instruments chirurgicaux peut provoquer une desorientation. Ainsi, la courbe d’apprentissage pour l’utilisation de cette technologie est tres abrupte et un nombre restreint de chirurgiens choisissent l’intervention minimalement invasive malgre les avantages qu’elle peut procurer aux patients. En effet la discectomie par thoracoscopie reduit les pertes sanguines, le traumatisme des tissus entourant le disque afin d’acceder a la zone d’interet et le temps d’hospitalisation. Les discectomies sont prescrites a certains patients scoliotiques afin de redonner de la flexibilite a la colonne avant l’instrumentation (pose de vis et tige pour corriger la deformation). La resection du disque intervertebral est faite partielleme...

BMC Medical Imaging, 2012

Background For some scoliotic patients the spinal instrumentation is inevitable. Among these pati... more Background For some scoliotic patients the spinal instrumentation is inevitable. Among these patients, those with stiff curvature will need thoracoscopic disk resection. The removal of the intervertebral disk with only thoracoscopic images is a tedious and challenging task for the surgeon. With computer aided surgery and 3D visualisation of the interverterbral disk during surgery, surgeons will have access to additional information such as the remaining disk tissue or the distance of surgical tools from critical anatomical structures like the aorta or spinal canal. We hypothesized that automatically extracting 3D information of the intervertebral disk from MR images would aid the surgeons to evaluate the remaining disk and would add a security factor to the patient during thoracoscopic disk resection. Methods This paper presents a quantitative evaluation of an automatic segmentation method for 3D reconstruction of intervertebral scoliotic disks from MR images. The automatic segmenta...

Hyperspectral (HSI) retinal imaging is an emergent modality for disease diagnosis such as diabeti... more Hyperspectral (HSI) retinal imaging is an emergent modality for disease diagnosis such as diabetic retinopathy. HSI represents the retina as a 3D cube, with two spatial dimensions and one spectral, meaning that spectral signatures associated with a disease may be identified. The quality of this hypercube influences the accuracy of automatic diagnosis. Three main artifacts may limit the hypercube’s quality: parasitic contribution (e.g. blinking or ghost), uneven illumination and blurriness. We present a method for artifact detection and quality assessment using SURF features and intensity-based analysis. Quality evaluation has a rich literature in classic fundus images. However, none of these works have tackled the challenges related to HSI. Hypercubes from volunteers recruited at an eye clinic, in reflectance (48) and fluorescence (32) imaging modes, were captured using a Metabolic Hyperspectral Retinal Camera based on a tuneable light source in the visible and near infrared spectra...

Alzheimer's & Dementia: Translational Research & Clinical Interventions

Journal of Magnetic Resonance Imaging

ABSTRACT RÉSUMÉ: Lors de discectomie par thoracoscopie, les outils de visualisation procurent peu... more ABSTRACT RÉSUMÉ: Lors de discectomie par thoracoscopie, les outils de visualisation procurent peu d’information de profondeur et le champ de visualisation de la caméra miniature insérée dans le patient est relativement restreint. Aussi, le mouvement simultané de la caméra et des instruments chirurgicaux peut provoquer une désorientation. Ainsi, la courbe d’apprentissage pour l’utilisation de cette technologie est très abrupte et un nombre restreint de chirurgiens choisissent l’intervention minimalement invasive malgré les avantages qu’elle peut procurer aux patients. En effet la discectomie par thoracoscopie réduit les pertes sanguines, le traumatisme des tissus entourant le disque afin d’accéder à la zone d’intérêt et le temps d’hospitalisation. Les discectomies sont prescrites à certains patients scoliotiques afin de redonner de la flexibilité à la colonne avant l’instrumentation (pose de vis et tige pour corriger la déformation). La résection du disque intervertébral est faite partiellement et la quantité du disque réséqué dépend du degré de flexibilité que le chirurgien désire redonner au patient. En effectuant la discectomie par thoracoscopie, il est impossible pour le chirurgien de visualiser rapidement la quantité de disque restant en plus d’avoir les désavantages de désorientation et de petit champ de vision de la caméra miniature insérée dans le patient. Il est donc pertinent de tenter de réduire les problèmes de visualisation rencontrés lors des thoracoscopies en procurant au chirurgien la possibilité d’examiner en 3D les structures anatomiques du patient pendant la chirurgie sans ajouter de radiations supplémentaires au patient. Ce système d’assistance permettrait également d’accroître la sécurité du patient et la qualité de la chirurgie en donnant aux chirurgiens la possibilité de localiser en 3D la moelle épinière et en leur donnant également la possibilité de visualiser la quantité de disque restant. Ainsi, l’intérêt de fusionner les images vidéo avec un modèle pré-opératoire 3D est alors tout indiqué.---------- ABSTRACT: Visualization tools available while doing thoracoscopic diskectomy do not show depth information and the field of view of the miniaturized camera inserted into the patient is small. Also, simultaneous movement of the camera and surgical tools may result in disorientation. The learning curve for the use of this technology is very steep and numbers of surgeons choose not to use minimally invasive surgery despite important advantages for the patients. Indeed, thoracoscopic diskectomy reduce blood loss, trauma of surrounding soft tissues to access intervertebral disks and hospitalization time. Diskectomy are prescribed to specific scoliotic patients to gain flexibility of the spine before instrumentation surgery (fixation of screws and rod to correct the deformation). The intervertebral disk is partly resected depending on the level of flexibility the patient has to gain according to the surgeon. During thoracoscopic diskectomy, it is impossible for the surgeon to rapidly visualize the remaining disk tissue and this further increase the disadvantages for the surgeons. Hence, it is relevant to try to reduce visualization problems encountered during thoracoscopic diskectomy by providing to the surgeons a 3D view of the whole spine during the surgery, without adding supplementary radiation to the patient. The computer assisted surgery system would also increase the security of the patient by allowing the surgeons to localize rapidly in 3D the spinal canal as well as the remaining disk. The fusion of the video images with 3D spine of the patient is of great interest for the surgeons.

Lecture Notes in Computer Science, 2007

A robust method to segment intervertebral disks and spinal canal in magnetic resonance images is ... more A robust method to segment intervertebral disks and spinal canal in magnetic resonance images is required as part of a precise 3D reconstruction for computer assistance during diskectomy procedure with minimally invasive surgery approach. In this paper, an unsupervised segmentation technique for intervertebral disks and spinal canal from MRI data is presented. The proposed scheme uses a watershed transform and morphological operations to locate regions containing structures of interest. Results show that the method is robust enough to cope with variability of shapes and topologies characterizing MRI images of scoliotic patients.

Clinical and Translational Neurophotonics 2019