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Vincent Luboz

Publications and source records attributed to Vincent Luboz.

14 recordsLinked to original sources
arXiv2018

Personalized modeling for real-time pressure ulcer prevention in sitting posture

, Ischial pressure ulcer is an important risk for every paraplegic person and a major public health issue. Pressure ulcers appear following excessive compression of buttock's soft tissues by bony structures, and particularly in ischial and sacral bones. Current prevention techniques are mainly based on daily skin inspection to spot red patches or injuries. Nevertheless, most pressure ulcers occur internally and are difficult to detect early. Estimating internal strains within soft tissues could help to evaluate the risk of pressure ulcer. A subject-specific biomechanical model could be used to assess internal strains from measured skin surface pressures. However, a realistic 3D non-linear Finite Element buttock model, with different layers of tissue materials for skin, fat and muscles, requires somewhere between minutes and hours to compute, therefore forbidding its use in a real-time daily prevention context. In this article, we propose to optimize these computations by using a reduced order modeling technique (ROM) based on proper orthogonal decompositions of the pressure and strain fields coupled with a machine learning method. ROM allows strains to be evaluated inside the model interactively (i.e. in less than a second) for any pressure field measured below the buttocks. In our case, with only 19 modes of variation of pressure patterns, an error divergence of one percent is observed compared to the full scale simulation for evaluating the strain field. This reduced model could therefore be the first step towards interactive pressure ulcer prevention in a daily setup. Highlights-Buttocks biomechanical modelling,-Reduced order model,-Daily pressure ulcer prevention.

physics.med-ph↗
arXiv2014

Smart Diabetic Socks: Embedded device for diabetic foot prevention

1) Objectives Most foot ulcers are the consequence of a trauma (repetitive high stress, ill-fitting footwear, or an object inside the shoe) associated to diabetes. They are often followed by amputation and shorten life expectancy. This paper describes the prototype of the Smart Diabetic Socks that has been developed in the context of the French ANR TecSan project. The objective is to prevent pressure foot ulcers for diabetic persons. 2) Material and methods A fully wireless, customizable and washable "smart sock" has been designed. It is made of a textile which fibers are knitted in a way they provide measurements of the pressure exerted under and all around the foot in real-life conditions. This device is coupled with a subject-specific Finite Element foot model that simulates the internal strains within the soft tissues of the foot. 3) Results A number of derived stress indicators can be computed based on that analysis, such as the accumulated stress dose, high internal strains or peak pressures near bony prominences during gait. In case of risks for pressure ulcer, an alert is sent to the person and/or to the clinician. A watch, a smart-phone or a distant laptop can be used for providing such alert.

physics.med-ph↗
arXiv2007

Intra-operative quantification of the surgical gesture in orbital surgery: Application to the proptosis reduction

Proptosis is characterized by a protrusion of the eyeball due to an increase of the orbital tissue volume. To recover a normal eyeball positioning, the most frequent surgical technique (BROD technique) consists in the osteotomy of orbital walls combined with a loading on the eyeball to initiate tissue decompression. This paper proposed an experimental method to quantify the intra-operative clinical gesture in proptosis reduction, and the pilot study concerned one clinical case. The eyeball's backward displacement was measured by an optical 3D localizer and the load applied by the surgeon was simultaneously measured by a custom-made force gauge. Quasi-static stiffness of the intra-orbital content was evaluated. The average values for the whole experiment was 16 N (SD: 3 N) for the force exerted by the surgeon and 9 mm (SD: 4 mm) for the eyeball backward displacement. The averaged quasi-static stiffness of the orbital content was evaluated to 2.4 N/mm (SD: 1.2) and showed a global decrease of 45% post-operatively.

physics.med-ph↗
arXiv2006

A 3D Finite Element evaluation of the exophthalmia reduction

This paper presents a first evaluation of the feasibility of Finite Element modelling of the orbital decompression, in the context of exophthalmia. First simulations are carried out with data extracted from a patient TDM exam. Results seem to qualitatively validate the feasibility of the simulations, with a Finite Element analysis that converges and provides a backward movement of the ocular globe associated with displacements of the fat tissues through the sinuses. This FE model can help a surgeon for the planning of the exophthalmia reduction, and especially for the position and the size of the decompression hole. To get an estimation of the fat tissues volume affected by the surgery, an analytical model seems to provide quicker results for an equivalent efficiency.

physics.med-ph↗
arXiv2006

A stiffness sensor to help in the diagnosis and the surgery of orbital pathologies

Proptosis is characterized by a protrusion of the eyeball due to an increase of the orbital tissue volume. To recover a normal eyeball positioning, the most frequent surgical technique (BROD technique) consists in the osteotomy of orbital walls combined with a loading on the eyeball to initiate tissue decompression. In this paper, a stiffness sensor device is proposed to (1) provide to the surgeon pre, intra and post-operative data concerning the stiffness of the intra-orbital soft tissues, and (2) provide constitutive parameters to the Finite Element model of the intra-orbital tissues already developed by the authors and used to predict consequences orbital surgery.

physics.med-ph↗
arXiv2006

Biomechanics applied to computer-aided diagnosis: examples of orbital and maxillofacial surgeries

This paper introduces the methodology proposed by our group to model the biological soft tissues deformations and to couple these models with Computer-Assisted Surgical (CAS) applications. After designing CAS protocols that mainly focused on bony structures, the Computer Aided Medical Imaging group of Laboratory TIMC (CNRS, France) now tries to take into account the behaviour of soft tissues in the CAS context. For this, a methodology, originally published under the name of the Mesh-Matching method, has been proposed to elaborate patient specific models. Starting from an elaborate manually-built "generic" Finite Element (FE) model of a given anatomical structure, models adapted to the geometries of each new patient ("patient specific" FE models) are automatically generated through a non-linear elastic registration algorithm. This paper presents the general methodology of the Mesh-Matching method and illustrates this process with two clinical applications, namely the orbital and the maxillofacial computer-assisted surgeries.

physics.med-ph↗
arXiv2006

A finite element study of the influence of the osteotomy surface on the backward displacement during exophthalmia reduction

Exophthalmia is characterized by a protrusion of the eyeball. The most frequent surgery consists in an osteotomy of the orbit walls to increase the orbital volume and to retrieve a normal eye position. Only a few clinical obser-vations have estimated the relationship between the eyeball backward dis-placement and the decompressed fat tissue volume. This paper presents a method to determine the relationship between the eyeball backward displace-ment and the osteotomy surface made by the surgeon, in order to improve ex-ophthalmia reduction planning. A poroelastic finite element model involving morphology, material properties of orbital components, and surgical gesture is proposed to perform this study on 12 patients. As a result, the osteotomy sur-face seems to have a non-linear influence on the backward displacement. More-over, the FE model permits to give a first estimation of an average law linking those two parameters. This law may be helpful in a surgical planning frame-work.

physics.med-ph↗
arXiv2006

Simulation of the Exophthalmia Reduction using a Finite Element Model of the Orbital Soft Tissues

This paper proposes a computer-assisted system for the surgical treatment of exophthalmia. This treatment is classically characterized by a de-compression of the orbit, by the mean of an orbital walls osteotomy. The plan-ning of this osteotomy consists in defining the size and the location of the de-compression hole. A biomechanical model of the orbital soft tissues and its in-teractions with the walls are provided here, in order to help surgeons in the definition of the osteotomy planning. The model is defined by a generic Finite Element poro-elastic mesh of the orbit. This generic model is automatically adapted to the morphologies of four patients, extracted from TDM exams. Four different FE models are then generated and used to simulate osteotomies in the maxillary or ethmoid sinuses regions. Heterogeneous results are observed, with different backwards movements of the ocular globe according to the size and/or the location of the hole.

physics.med-ph↗
arXiv2006

Orbital and Maxillofacial Computer Aided Surgery: Patient-Specific Finite Element Models To Predict Surgical Outcomes

This paper addresses an important issue raised for the clinical relevance of Computer-Assisted Surgical applications, namely the methodology used to automatically build patient-specific Finite Element (FE) models of anatomical structures. From this perspective, a method is proposed, based on a technique called the Mesh-Matching method, followed by a process that corrects mesh irregularities. The Mesh-Matching algorithm generates patient-specific volume meshes from an existing generic model. The mesh regularization process is based on the Jacobian matrix transform related to the FE reference element and the current element. This method for generating patient-specific FE models is first applied to Computer-Assisted maxillofacial surgery, and more precisely to the FE elastic modelling of patient facial soft tissues. For each patient, the planned bone osteotomies (mandible, maxilla, chin) are used as boundary conditions to deform the FE face model, in order to predict the aesthetic outcome of the surgery. Seven FE patient-specific models were successfully generated by our method. For one patient, the prediction of the FE model is qualitatively compared with the patient's post-operative appearance, measured from a Computer Tomography scan. Then, our methodology is applied to Computer-Assisted orbital surgery. It is, therefore, evaluated for the generation of eleven patient-specific FE poroelastic models of the orbital soft tissues. These models are used to predict the consequences of the surgical decompression of the orbit. More precisely, an average law is extrapolated from the simulations carried out for each patient model. This law links the size of the osteotomy (i.e. the surgical gesture) and the backward displacement of the eyeball (the consequence of the surgical gesture).

physics.med-ph↗
arXiv2006

Prediction of tissue decompression in orbital surgery

Objective: A method to predict the relationships between decompressed volume of orbital soft tissues, backward displacement of globe after osteotomy, and force exerted by the surgeon, was proposed to improve surgery planning in exophthalmia reduction. Design: A geometric model and a poroelastic finite element model were developed, based on Computed Tomography scan data. Background: The exophthalmia is characterised by a protrusion of the eyeball. Surgery consists in an osteotomy of the orbit walls to decompress the orbital content. A few clinical observations ruling on an almost linear relationship between globe backward displacement and tissue decompressed volume are described in the literature. Methods: Fast prediction of decompressed volume is derived from the geometric model: a sphere in interaction with a cone. Besides, a poroelastic Finite Element model involving morphology, material properties of orbital components and surgical gesture was implemented. Results: The geometric model provided a better decompression volume estimation than the Finite Element model. Besides, the Finite Element model permitted to quantify the backward displacement, the surgical gesture and the stiffness of the orbital content. Conclusions: The preliminary results obtained for one patient, in accordance with the clinical literature, were relatively satisfying. An efficient aid for location and size of osteotomies was derived and seemed to be able to help in the surgery planning. Relevance: To our knowledge, this paper concerns the first biomechanical study of exophthalmia reduction. The approach permitted to improve the treatment of orbitopathy and can be used in a clinical setting.

physics.med-ph↗
arXiv2006

Biomechanical models to simulate consequences of maxillofacial surgery

This paper presents the biomechanical finite element models that have been developed in the framework of the computer-assisted maxillofacial surgery. After a brief overview of the continuous elastic modelling method, two models are introduced and their use for computer-assisted applications discussed. The first model deals with orthognathic surgery and aims at predicting the facial consequences of maxillary and mandibular osteotomies. For this, a generic three-dimensional model of the face is automatically adapted to the morphology of the patient by the mean of elastic registration. Qualitative simulations of the consequences of an osteotomy of the mandible can thus be provided. The second model addresses the Sleep Apnoea Syndrome. Its aim is to develop a complete modelling of the interaction between airflow and upper airways walls during respiration. Dynamical simulations of the interaction during a respiratory cycle are computed and compared with observed phenomena.

physics.med-ph↗
arXiv2006

Computer assisted planning and orbital surgery: patient-related prediction of osteotomy size in proptosis reduction

BACKGROUND: Proptosis is characterized by a protrusion of the eyeball due to an increase of the orbital tissue volume. To recover a normal eyeball positioning, the most frequent surgical technique consists in the osteotomy of orbital walls combined with the manual loading on the eyeball. Only a rough clinical rule is currently available for the surgeons but it is useless for this technique. The first biomechanical model dealing with proptosis reduction, validated in one patient, has been previously proposed by the authors. METHODS: This paper proposes a rule improving the pre-operative planning of the osteotomy size in proptosis reduction. Patient-related poroelastic FE models combined with sensitivity studies were used to propose two clinical rules to improve the pre-operative planning of proptosis reduction. This poroelastic model was run on 12 patients. Sensitivity studies permitted to establish relationships between the osteotoemy size, the patient-related orbital volume, the decompressed tissue volume and the eyeball backward displacement. FINDINGS: The eyeball displacement and the osteotomy size were non-linearly related: an exponential rule has been proposed. The patient-related orbital volume showed a significant influence: a bi-quadratic analytical equation liking the osteotomy size, the orbital volume and the targeted eyeball protrusion has been established. INTERPRETATION: Two process rules derived from patient-related biomechanical FE models have been proposed for the proptosis reduction planning. The implementation of the process rules into a clinical setting is easy since only a sagittal radiography is required. The osteotomy size can be monitored using optical guided instruments.

physics.med-ph↗