The Mesh-Matching algorithm: a new automatic 3D mesh generator for Finite Element analysis

This paper deals with Finite Element (FE) modeling of human body structures. More specifically, it focuses on the FE mesh generation process, which is a long and tedious task in the case of irregular and non-homogeneous structures. Whereas for regular and symmetrical bodies (like in the architectural domain for example), some automatic mesh generators have been developed, no robust system is provided for living structures, which are, by definition, non-homogeneous, irregular and patient-specific. This paper proposes a new algorithm, called the mesh-matching (M-M) algorithm, that automatically generates patient-specific 3D meshes for FE models of structures with complex geometry. It assumes that the shape which is studied is sufficiently close to a known “standard” model for which a mesh has been already generated by an expert. The algorithm proposes then to use a registration method, in order to infer the “standard” finite element mesh to the data. The M-M algorithm is tested and initially validated on five human femurs

Liquid Calibration Phantoms in Ultra-Low-Dose QCT for the Assessment of Bone Mineral Density

Introduction: Cortical bone is affected by metabolic diseases. Some studies have shown that lower cortical bone mineral density (BMD) is related to increases in fracture risk which could be diagnosed by quantitative computed tomography (QCT). Nowadays, hybrid iterative reconstruction-based (HIR) computed tomography (CT) could be helpful to quantify the peripheral bone tissue. A key focus of this paper is to evaluate liquid calibration phantoms for BMD quantification in the tibia and under hybrid iterative reconstruction-based-CT with the different hydrogen dipotassium phosphate (K 2 HPO 4 ) concentrations phantoms. Methodology: Four ranges of concentrations of K 2 HPO 4 were made and tested with 2 exposure settings. Accuracy of the phantoms with ash gravimetry and intermediate K 2 HPO 4 concentration as hypothetical patients were evaluated. The correlations and mean differences between measured equivalent QCT BMD and ash density as a gold standard were calculated. Relative percentage error (RPE) in CT numbers of each concentration over a 6-mo period was reported. Results: The correlation values (R 2 was close to 1.0), suggested that the precision of QCT-BMD measurements using standard and ultra-low dose settings were similar for all phantoms. The mean differences between QCT-BMD and the ash density for low concentrations (about 93 mg/cm 3 ) were lower than high concentration phantoms with 135 and 234 mg/cm 3 biases. In regard to accuracy test for hypothetical patient, RPE was up to 16.1 for the low concentration (LC) phantom for the case of high mineral content. However, the lowest RPE (0.4 to 1.8) was obtained for the high concentration (HC) phantom, particularly for the high mineral content case. In addition, over 6 months, the K 2 HPO 4 concentrations increased 25 for 50 mg/cm 3 solution and 0.7 for 1300 mg/cm 3 solution in phantoms. Conclusion: The excellent linear correlations between the QCT equivalent density and the ash density gold standard indicate that QCT can be used with submilisivert radiation dose. We conclude that using liquid calibration phantoms with a range of mineral content similar to that being measured will minimize bias. Finally, we suggest performing BMD measurements with ultra-low dose scan concurrent with iterative-based reconstruction to reduce radiation exposure. © 2019 The International Society for Clinical Densitometr

Prediction of biomechanical parameters of the proximal femur using statistical appearance models and support vector regression

Fractures of the proximal femur are one of the principal causes of mortality among elderly persons. Traditional methods for the determination of femoral fracture risk use methods for measuring bone mineral density. However, BMD alone is not sufficient to predict bone failure load for an individual patient and additional parameters have to be determined for this purpose. In this work an approach that uses statistical models of appearance to identify relevant regions and parameters for the prediction of biomechanical properties of the proximal femur will be presented. By using Support Vector Regression the proposed model based approach is capable of predicting two different biomechanical parameters accurately and fully automatically in two different testing scenarios

The stability of the femoral component of a minimal invasive total hip replacement system.

Item does not contain fulltextIn this study, the initial stability of the femoral component of a minimal invasive total hip replacement was biomechanically evaluated during simulated normal walking and chair rising. A 20 mm diameter canal was created in the femoral necks of five fresh frozen human cadaver bones and the femoral heads were resected at the smallest cross-sectional area of the neck. The relatively short, polished, taper-shaped prostheses were cemented centrally in this canal according to a standardized procedure. A servohydraulic testing machine was used to apply dynamic loads to the prosthetic head. Radiostereophotogrammetric analysis was used to measure rotations and translations between the prosthesis and bone. In addition, the reconstructions were loaded until failure in a static, displacement-controlled test. During the dynamic experiments, the femoral necks did not fail and no macroscopical damage was detected. Maximal values were found for normal walking with a mean rotation of about 0.2 degrees and a mean translation of about 120 microm. These motions stabilized during testing. The mean static failure load was 4714 N. The results obtained in this study are promising and warrant further development of this type of minimal invasive hip prosthesis