Examinando por Autor "Koutras, Christos"

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A study of the sensitivity of biomechanical models of the spine for scoliosis brace design
(Elsevier, 2021) Koutras, Christos; Pérez, Jesús; Kardash, Kateryna; Otaduy, Miguel A.
Background and Objective: The development of biomechanical models of the torso and the spine opens the door to computational solutions for the design of braces for adolescent idiopathic scoliosis. However, the design of such biomechanical models faces several unknowns, such as the correct identification of relevant mechanical elements, or the required accuracy of model parameters. The objective of this study was to design a methodology for the identification of the aforementioned elements, with the purpose of creating personalized models suited for patient-specific brace design and the definition of parameter estimation criteria. Methods: We have developed a comprehensive model of the torso, including spine, ribcage and soft tissue, and we have developed computational tools for the analysis of the model parameters. With these tools, we perform an analysis of the model under typical loading conditions of scoliosis braces. Results: We present a complete sensitivity analysis of the models mechanical parameters and a comparison between a reference healthy subject and a subject suffering from scoliosis. Furthermore, we make a direct connection between error bounds on the deformation and tolerances for parameter estimation, which can guide the personalization of the model. Conclusions: Not surprisingly, the stiffness parameters that govern the lateral deformation of the spine in the frontal plane are some of the most relevant parameters, and require careful modeling. More surprisingly, their relevance is on par with the correct parameterization of the soft tissue of the torso. For scoliosis patients, but not for healthy subjects, we observe that the axial rotation of the spine also requires careful modeling.
Modeling and Estimation of Personalized Spine and Torso Biomechanics
(Universidad Rey Juan Carlos, 2023) Koutras, Christos
Adolescent idiopathic scoliosis is a complex spinal deformity with a considerable prevalence that can lead to deterioration of life. Scoliosis problems of moderate degree on adolescents are typically treated using orthotic brace structures that push the spine; it is usually the only way to avoid or delay surgery. The development of personalized biomechanical models of the torso opens the door to computational solutions for the design of such braces. However, the development of patient-specific biomechanical models faces two challenges: Fitting the geometry of the torso skeleton to the patient’s anatomy and characterizing their personalized stiffness response. Before handling these challenges, the design of such models faces several unknowns, such as the correct identification of relevant mechanical elements, or the required accuracy of model parameters. In this thesis, we first design a methodology for the identification of the relevant mechanical elements, with the purpose of creating personalized models suited for patient-specific brace design and the definition of parameter estimation criteria. Next, we present a method to fit personalized geometric models of the torso skeleton that takes as input biplanar low-dose radiographs. The method relies on a biomecahnically inspired regularizer for robust fitting, and minimizes the radiation exposure compared to existing works. Finally, we describe a methodology to personalize the stiffness response of a biomechanical model of the torso and the spine. In high contrast to previous work, the proposed methodology uses controlled forcedeformation data that mimic the conditions of spinal bracing for scoliosis, which leads to personalized biomechanical models that are suitable for computational brace design. The novel method relies on a prototype system that includes controlled force-deformation measurements, a model of differentiable biomechanics of the torso, which becomes the key building block for robust parameter estimation, and an optimization procedure for parameter estimation which relies on differentiability of the biomechanics and the image generation process. Altogether, we present a method that deals with the full personalization of torso and spine models under end-to-end representative adolescent idiopathic scoliosis conditions. We demonstrate its applicability on a cohort of scoliosis patients and we show quantitative validation and improvement over previous work.
Non-invasive procedure for acquisition of mechanical properties of the torso
(-, 2022) Koutras, Christos; Shayestehpour, Hamed; Perez, Jesus; Wong, Christian; Arnesen, Anna; Rasmussen, John; Otaduy, Miguel A.
Computational methods promise benefits for the design of braces to manage adolescent idiopathic scoliosis. However, computational methods for the design of scoliosis braces suffer an important challenge: they require a personalized model of the patient’s torso biomechanics. The biggest difficulty in building a personalized model of the torso is defining its mechanical parametrization. In this work, we present a non-invasive procedure to obtain simultaneously force and deformation that characterize the mechanical response of the torso. We have tested the method on ten scoliotic patients, and we demonstrate its sensitivity by quantifying the range of forces and Cobb angles during the procedure.
Simulation-Based Morphing of Personalized Models of the Torso for Scoliosis Brace Design – Preliminary Results
(orthopaedic research society, 2022) Koutras, Christos; Shayestehpour, Hamed; Rodriguez, Jesus P.; Rasmussen, John; Wong, Christian; Otaduy, Miguel A.
Computational and personalized design of braces for patients suffering from adolescent idiopathic scoliosis is a subject that has not been extensively studied and faces several unknowns. One of the most challenging tasks is the development of patient-specific biomechanical models of the torso. The first step required in order to build a personalized model is the acquisition of the patient’s specific geometry, i.e., the bones and joints of the skeleton. To this end, this study morphs a template torso model into patient-specific data in the following way: We start by acquiring x-rays, and we annotate personalized landmarks. Then, we use as template a biomechanical torso model consisted of a multibody dynamic system coupled with FEM and we proceed to the morphing in two steps. First, an initial tuning by adjusting the global scale of the model and finally a finer one, taking into account local deformations.