Laurent Gajny

• PhD
• Professor (Associate) at École nationale supérieure d'arts et métiers

In this article, we address the problem of approximating data points by C1-smooth polynomial spline curves or surfaces using L1-norm. The use of this norm helps to preserve the data shape and it reduces extraneous oscillations. In our approach, we introduce a new functional which enables to control directly the distance between the data points and...

In this article, we adress the problem of approximating scattered data points by C 1-smooth polynomial spline curves using L 1-norm optimization. The use of this norm helps us to preserve the shape of the data even near to abrupt changes. We introduced a five-point sliding window process for L 1 spline approximation but this method can be still tim...

Dans cet article, nous traitons le problème d'approximation de nuages de points par une courbe spline ou surface au sens de la norme L1 . L'utilisation de cette norme permet de préserver la forme des données même en cas de changement brutal de celle-ci. Dans nos précédents travaux, nous avons introduit une méthode par fenêtre glissante de cinq poin...

In this article, we justify the use of parametric planar Pythagorean Hodograph spline curves in path planning. The elegant properties of such splines enable us to design an efficient interpolator algorithm, more precise than the classical Taylor interpolators and faster than an interpolator based on arc length computations.

Introduction: The diagnostic approach to facial asymmetries is classically based, in addition to the clinical examination, on a cephalometric analysis carried out on a frontal radiography. Planning of orthognathic surgery requires a three-dimensional (3D) examination to visualize deformities. Nevertheless, the use of cephalometric analysis on 3D i...

Objective To assess the accuracy of three commercially available and one open‐source deep learning (DL) solutions for automatic tooth segmentation in cone beam computed tomography (CBCT) images of patients with multiple dental impactions. Materials and Methods Twenty patients (20 CBCT scans) were selected from a retrospective cohort of individuals...

Background Few studies have assessed the participation of the spine in arm elevation. The primary aim of this exploratory study was to specify spinal movements during unilateral arm elevation. Methods We used an EOS imaging system to assess 2D global posture (Sagittal Vertical Axis [SVA], T1 and T9 tilt and Central Sacral Line [CSL]) and segmental...

Our objective was to analysis the barycentremetry, obtained from the external envelope reconstruction of biplanar radiographs, in adolescent idiopathic scoliosis (AIS) and to determine whether assessing would help predict the distinction between progressive and stable AIS at the early stage. A retrospective study with a multicentre cohort of 205 AI...

Periacetabular osteotomy is the gold standard treatment for acetabular dysplasia. The great variability of acetabular dysplasia requires a personalized preoperative planning improved by 3D reconstruction and computer-assisted surgery. To plan the displacement of the acetabular fragment by a pelvic osteotomy, it is necessary to define a reference pl...

Objectives Segmentation of anatomical structures on dento-maxillo-facial (DMF) computed tomography (CT) or cone beam computed tomography (CBCT) scans is increasingly needed in digital dentistry. The main aim of this research was to propose and evaluate a novel open source tool called DentalSegmentator for fully automatic segmentation of five anatom...

Clinical use of finite element analysis requires validation and reproducibility studies. The current study compared two models of vertebral bodies including endplates, on the same experimental dataset and evaluated the influence of the operator on the failure load. Models used were strongly correlated (R2 = 0.91). The intra-operator reproducibility...

Objectives Segmentation of anatomical structures on dento-maxillo-facial (DMF) computed tomography (CT) or cone beam computed tomography (CBCT) scans is increasingly needed in digital dentistry. The main aim of this research was to propose and evaluate a novel open source tool called DentalSegmentator for fully automatic segmentation of five anatom...

Introduction Our objective was to assess abnormalities of the odontoid-hip axis (OD-HA) angle in a mild scoliotic population to determine whether screening for malalignment would help predict the distinction between progressive and stable adolescent idiopathic scoliosis (AIS) at early stage. Materials and methods All patients (non-scoliotic and AI...

Barycentremetry in adolescent idiopathic scoliosis (AIS) allows the distribution of masses and their loading of the spine to be studied. In particular, the axial torque on the spine has been studied in AIS, but not after surgical correction. Spinal axial torque was studied in AIS before and after surgery. All AIS (Lenke 1 and 3) who underwent poste...

Les applications potentielles de l’intelligence artificielle, ces algorithmes visant à améliorer l’efficacité et la sécurité de diverses décisions cliniques, sont nombreuses en odontologie. Alors que les premiers logiciels commerciaux commencent à être proposés, la plupart des algorithmes n’ont pas été solidement validés pour une utilisation cliniq...

This study compared two models of vertebral bodies including endplates, on the same experimental dataset, and evaluated the influence of the operator on the failure load.

This study compared two models of vertebral bodies including endplates, on the same experimental dataset, and evaluated the influence of the operator on the failure load.

Models in literature are numerous but have been rarely applied on the same experimental datasets, restraining comparison between models [1]. Clinical use of finite element analysis requires a well-defined process. Consequently, this study compared two models of vertebral bodies including endplates, on the same experimental dataset and evaluated the...

The face blurring of images plays a key role in protecting privacy. However, in computer vision, especially for the human pose estimation task, machine-learning models are currently trained, validated, and tested on original datasets without face blurring. Additionally, the accuracy of human pose estimation is of great importance for kinematic anal...

The increasing use of 3-dimensional (3D) imaging by orthodontists and maxillofacial surgeons to assess complex dentofacial deformities and plan orthognathic surgeries implies a critical need for 3D cephalometric analysis. Although promising methods were suggested to localize 3D landmarks automatically, concerns about robustness and generalizability...

Study design: A monocentric, retrospective radiographic study with 99 asymptomatic volunteers. Objective: We performed the postural analysis commonly scheduled when evaluating sagittal balance in a vertebra-by-vertebra manner by enrolling an asymptomatic population. We measured the position and angulation of each vertebra to reveal those for whi...

Background Marker-less systems based on digital video cameras and deep learning for gait analysis could have a deep impact in clinical routine. A recently developed system has shown promising results in terms of joint center position but has not been yet evaluated in terms of gait outcomes. Research question How does this novel marker-less system...

Three-dimensional bone reconstructions from medical imaging are essential for biomechanical modelling and are growing tools in clinics. Several methods of lower limbs reconstruction from biplanar radiographs have been proposed in the literature but with significant operator dependence. A novel reconstruction method based on reduced manual annotatio...

The increasing use of three-dimensional (3D) imaging by orthodontists and maxillofacial surgeons to assess complex dentofacial deformities and plan orthognathic surgeries implies a critical need for 3D cephalometric analysis. Although promising methods were suggested to localize 3D landmarks automatically, concerns about robustness and generalizabi...

Objectives To evaluate the performance of the nnU-Net open-source deep learning framework for automatic multi-task segmentation of craniomaxillofacial (CMF) structures in CT scans obtained for computer-assisted orthognathic surgery.Methods Four hundred and fifty-three consecutive patients having undergone high-resolution CT scans before orthognathi...

Objective Surgical correction of thoracic scoliosis leads to a height improvement. Our objectives were to assess how the linear and developed spinal column lengths relate to the frontal and sagittal parameters after a surgical correction of thoracic idiopathic scoliosis, and whether the measurement of these lengths is reliable using quasi-automatic...

In some dentofacial deformity patients, especially patients undergoing surgical orthodontic treatments, Computed Tomography (CT) scans are useful to assess complex asymmetry or to plan orthognathic surgery. This assessment would be made easier for orthodontists and surgeons with a three-dimensional (3D) cephalometric analysis, which would require t...

Objective To identify the different apex and transitional vertebra according to the shape of the pelvis of individuals despite their difference in sagittal alignment using our measurement system.Methods Full-spine X-rays using EOS in standard stand-position of 99 volunteers were selected (47 women, 52 men, mean age 31 years old). Validated 3D recon...

EOS biplane radiographs of 117 subjects between 20 and 83 years were analyzed to compute the upper body lever arm over the L1 vertebra and its impact on vertebral strength. Postural sagittal alignment alteration was observed with age and resulted in a greater lever arm causing vertebral strength to decrease. Purpose: The purpose of this study was...

Objectives To evaluate the performance of the nnU-Net open-source deep learning framework for automatic multi-task segmentation of craniomaxillofacial (CMF) structures in CT scans obtained for computer-assisted orthognathic surgery. Methods Four hundred and fifty-three consecutive patients having undergone high-definition CT scans before orthognat...

AIM Accurate segmentation of computed tomography (CT) scans is needed for computer-assisted planning and personalized implant manufacturing for orthognathic surgery. Accurate segmentation of these scans is challenging due to large interindividual morphological variations, tight connections between the structures and artifacts. In this study, we ev...

Objective Our objective was to establish a corridor of normality for the external shape 3D parameters and then to assess these variables in adolescent idiopathic scoliosis (AIS). Methods Adolescent with mild and severe AIS were included prospectively, as well as a control group of asymptomatic subjects. A quasi‐automatic 3D reconstruction of the s...

Background: Biplanar X-ray system providing anteroposterior and sagittal plane with an ultra-low radiation dose and in weight-bearing position is increasingly used for spine imaging. The original three-dimensional (3D) reconstruction method from biplanar X-rays has been widely used for clinical parameters, however, the main issue is that manual ad...

Background The deep learning-based human pose estimation methods, which can estimate joint centers position, have achieved promising results on the publicly available human pose datasets (e.g., Human3.6 M). However, these datasets may be less efficient for gait study, particularly for clinical applications, because of the limited number of subjects...

Background: Balanced global spinopelvic balance is important in the maintenance of the physiological alignment of all body segments above the pelvis with minimum energy expenditure. The key determinants affecting the 3D index-odontoid-hip axis (OD-HA) angle, and in particular its alterations, have not been clearly defined. The aim of this study is...

PurposeThe aim of this work is to propose a classification algorithm to automatically detect treatment for scoliosis (brace, implant or no treatment) in postero-anterior radiographs. Such automatic labelling of radiographs could represent a step towards global automatic radiological analysis.Methods Seven hundred and ninety-six frontal radiographie...

The aim of this systematic review was to assess the accuracy and reliability of automatic landmarking for cephalometric analysis of three-dimensional craniofacial images. We searched for studies that reported results of automatic landmarking and/or measurements of human head computed tomography or cone beam computed tomography scans in MEDLINE, Emb...

3D reconstruction from low-dose Bi-Planar X-Rays (BPXR) is a rising practice in clinical routine. However, this process is time consuming and highly depends on the user. This study aims to partially automate the process for the femur, thus decreasing reconstruction time and increasing robustness. As a training set, 50 femurs are segmented from CT s...

Purpose Measurement of vertebral axial rotation (VAR) is relevant for the assessment of scoliosis. Stokes method allows estimating VAR in frontal X-rays from the relative position of the pedicles and the vertebral body. This method requires identifying these landmarks for each vertebral level, which is time-consuming. In this work, a quasi-automate...

L’analyse céphalométrique est une méthode diagnostique standardisée qui est utilisée quotidiennement par les orthodontistes et les chirurgiens maxillo-faciaux. Cet examen est traditionnellement effectué manuellement sur des radiographies 2D, ce qui ne permet pas d’analyser finement les structures bilatérales qui se retrouvent superposées. L’analys...

Manually annotating medical images with few landmarks to initialize 3D shape models is a common practice. For instance, when reconstructing the 3D spine from biplanar X-rays, the spinal midline, passing through vertebrae body centers (VBCs) and endplate midpoints, is required. This paper presents an automated spinal midline delineation method on fr...

Human pose estimation (HPE) methods based on convolutional neural networks (CNN) have demonstrated significant progress and achieved state-of-the-art results on human pose datasets. In this study, we aimed to assess the performance of CNN-based HPE methods for measuring anthropometric data. A Vicon motion analysis system as the reference system and...

Purpose To validate the predictive power and reliability of a novel quasi-automatic method to calculate the severity index of adolescent idiopathic scoliosis (AIS). Methods Fifty-five AIS patients were prospectively included (age 10–15, Cobb 16° ± 4°). Patients underwent low-dose biplanar X-rays, and a novel fast method for 3D reconstruction of th...

Purpose To design a quasi-automated three-dimensional reconstruction method of the spine from biplanar X-rays as the daily used method in clinical routine is based on manual adjustments of a trained operator and the reconstruction time is more than 10 min per patient. Methods The proposed method of 3D reconstruction of the spine (C3–L5) relies fir...

Adolescent idiopathic scoliosis (AIS) is a 3D deformity of the spine detectable by trunk asymmetry. As a decision-aid tool, body scanners can assess non-invasively the external shape of the trunk. If AIS is diagnosed, additional 3D reconstructions of the spine, rib cage and pelvis are useful to plan a treatment such as bracing. Body scanners cannot...

Best $L_1$ approximation of the Heaviside function and best $\ell_1$ approximation of multiscale univariate datasets by cubic splines have a Gibbs phenomenon. Numerical experiments show that it can be reduced by using $L_1$ spline fits which are best $L_1$ approximations in an appropriate spline space obtained by the union of $L_1$ interpolation sp...

Quantitative measurements of spine shape parameters on planar X-rays is critical for clinical applications, but remains tedious and with no fully automated solution demonstrated on the whole spine. This study aims to limit manual input, while demonstrating precise vertebrae corners positioning and shape parameter measurements from sagittal radiogra...

In this article, we study the problem of best L 1 approximation of Heaviside-type functions from Chebyshev and weak-Chebyshev spaces. We extend the Hobby-Rice theorem (Proc. Am. Math. Soc., 16, 665–670, 1965) into an appropriate framework and prove the unicity of best L 1 approximation of Heaviside-type functions from an even-dimensional Chebyshev...

Best $L_1$ approximation of the Heaviside function and best $\ell_1$ approximation of multiscale univariate datasets by cubic splines have a Gibbs phenomenon. Numerical experiments show that it can be reduced by using $L_1$ spline fits which are best $L_1$ approximations in an appropriate spline space obtained by the union of $L_1$ interpolation sp...

Data and function approximation is fundamental in application domains like path planning or signal processing (sensor data). In such domains, it is important to obtain curves that preserve the shape of the data. Considering the results obtained for the problem of data interpolation, L1 splines appear to be a good solution. Contrary to classical L2...

Spline fits are calculated by minimizing a data fitting functional over a manifold of splines. The class of cubic L1 spline fits, introduced in [Lav04], has the advantage to not introduce extraneous oscillations on multi-scale data contrary to least-squares spline fits. Cubic L1 spline fits are calculated by a Lagrange-multiplier-based primal affin...

Afin d’accroître leur compétitivité les entreprises ont recours de plus en plus à des systèmes robotisés pour realiser différentes tâches complexes. Ces robots sont très attractifs par leur coût mais nécessitent d’introduire des capteurs externes afin de garantir une plus grande précision de mouvement. Un enjeu majeur concerne la co-activité avec l...