Framework for a low-cost intra-operative image-guided neuronavigator including brain shift compensation

In this paper we present a methodology to address the problem of brain tissue deformation referred to as 'brain-shift'. This deformation occurs throughout a neurosurgery intervention and strongly alters the accuracy of the neuronavigation systems used to date in clinical routine which rely solely on pre-operative patient imaging to locate the surgical target, such as a tumour or a functional area. After a general description of the framework of our intra-operative image-guided system, we describe a procedure to generate patient specific finite element meshes of the brain and propose a biomechanical model which can take into account tissue deformations and surgical procedures that modify the brain structure, like tumour or tissue resection

A fast and robust patient specific Finite Element mesh registration technique: application to 60 clinical cases

Finite Element mesh generation remains an important issue for patient specific biomechanical modeling. While some techniques make automatic mesh generation possible, in most cases, manual mesh generation is preferred for better control over the sub-domain representation, element type, layout and refinement that it provides. Yet, this option is time consuming and not suited for intraoperative situations where model generation and computation time is critical. To overcome this problem we propose a fast and automatic mesh generation technique based on the elastic registration of a generic mesh to the specific target organ in conjunction with element regularity and quality correction. This Mesh-Match-and-Repair (MMRep) approach combines control over the mesh structure along with fast and robust meshing capabilities, even in situations where only partial organ geometry is available. The technique was successfully tested on a database of 5 pre-operatively acquired complete femora CT scans, 5 femoral heads partially digitized at intraoperative stage, and 50 CT volumes of patients' heads. The MMRep algorithm succeeded in all 60 cases, yielding for each patient a hex-dominant, Atlas based, Finite Element mesh with submillimetric surface representation accuracy, directly exploitable within a commercial FE software

Influence of walnut trees (Juglans regia L.) on soil urease activity

Soil urease is an enzyme catalyzing the hydrolysis of urea. The activity of the enzyme influences the content of ammonia ions in soil and thereby the fertility of the soil. 5-hydroxy-1,4-naphthalenedione (juglone) is a compound which inhibits urease. The compound is released by trees of the Juglandaceae family (walnut trees) and is present in their leaves, roots, husks and fruits. The aim of the study was to determine the effect of walnut trees on the activity of soil urease. Urease activity was determined in the soil beneath the tree crown and beyond.It has been shown that soil urease activity is higher in the area outside of the tree crown than beneath it. Less active urease slows down the natural nitrogen cycle resulting in decreased soil fertility. The lower soil fertility slows the growth of plants. This shows non direct influence of juglone on the growth of plants in the vicinity of walnut trees.The greatest difference in urease activity beneath and beyond the crown was observed near the oldest tree. This indicates that the development of the crown and root system increases the amount of secreted juglone.Soil active acidity and exchange acidity were measured. The study did not show a significant correlation between soil urease activity and soil acidity in the observed pH range

Bio-Mechanical Model of the Brain for a Per-Operative Image-Guided Neuronavigator Compensating for "Brain-Shift" Deformations

In this paper we present a methodology to address the problem of brain tissue deformation referred to as 'brain-shift'. This deformation occurs throughout a neurosurgery intervention and strongly alters the accuracy of the neuronavigation systems used to date in clinical routine which rely solely on pre-operative patient imaging to locate the surgical target, such as a tumour or a functional area. After a general description of the framework of our intra-operative image-guided system, we describe a procedure to generate patient specific finite element meshes of the brain and propose a biomechanical model which can take into account tissue deformations and surgical procedures that modify the brain structure, like tumour or tissue resection

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

3D musculo-skeletal finite element analysis of the foot kinematics under muscle activation with and without ankle arthrodesis

International audienceThe choice between arthrodesis and arthroplasty in the context of advanced ankle arthrosis remains a highly disputed topic in the field of foot and ankle surgery. Arthrodesis, however, represents the most popular option. Biomechanical modeling has been widely used to investigate static loading of cadaveric feet as well as consequences of arthrodesis on bony structures. Although foot kinematics has been studied using motion analysis, this approach lacks accuracy in capturing internal joints motion due to limitations inherent to external “marker sets” and the fact that it imposed the foot to be considered as a rigid solid. The consequences of arthrodesis on kinematics of the unloaded foot are not well understood although it is of crucial importance during the swing phase and at heel contact. Investigating ankle mobility during muscle contraction with and without arthrosis could explain how the motion is produced by extrinsic muscles activations affected by an arthrodesis. This study aims at defining if a biomechanical model with Finite Elements could help arthrodesis understanding

Using a smart phone for information rendering in Computer-Aided Surgery

Computer-aided surgery intensively uses the concept of navigation: after having collected CT data from a patient and transferred them to the operating room coordinate system, the surgical instrument (a puncture needle for instance) is localized and its position is visualized with respect to the patient organs which are not directly visible. This approach is very similar to the GPS paradigm. Traditionally, three orthogonal slices in the patient data are presented on a distant screen. Sometimes a 3D representation is also added. In this study we evaluated the potential of adding a smart phone as a man-machine interaction device. Different experiments involving operators puncturing a phantom are reported in this paper

Multi-modal framework for subject-specific finite element model generation aimed at pressure ulcer prevention.

International audienceThis study outlines a methodology aiming at the definition of an individual and personalised pressure ulcer risk assessment scale based on patient-specific biomechanical modellin

Multi-Modal Framework for Subject-Specific Finite Element Modeling of the Buttocks

International audienceIn order to produce high quality personalized FE models, it is necessary to resort to medical imaging and acquire the most relevant possible description of the modeled morphology. Yet building a FE model from a medical data set can be a challenging and time consuming task. To overcome the commonly encountered problems, this paper introduces a "mesh warping" approach chosen for its versatility. A biomechanical finite element model of the buttocks soft tissues is generated for an efficient prevention of pressure ulcers

Biomechanical Modeling to Prevent Ischial Pressure Ulcers

International audienceWith 300,000 paraplegic persons only in France, ischial pressure ulcers represent a major public health issue. They result from the buttocks' soft tissues compression by the bony prominences. Unfortunately, the current clinical techniques, with - in the best case - embedded pressure sensor mats, are insufficient to prevent them because most are due to high internal strains which can occur even with low pressures at the skin surface. Therefore, improving prevention requires using a biomechanical model to estimate internal strains from skin surface pressures. However, the buttocks' soft tissues' stiffness is still unknown. This paper provides a stiffness sensitivity analysis using a finite element model. Different layers with distinct Neo Hookean materials simulate the skin, fat and muscles. With Young moduli in the range [100 - 500 kPa], [25 - 35 kPa], and [80 - 140 kPa] for the skin, fat, and muscles respectively, maximum internal strains reach realistic 50 to 60 % values. The fat and muscle stiffnesses have an important influence on the strain variations, while skin stiffness is less influent. Simulating different sitting postures and changing the muscle thickness also result in a variation in the internal strains