International Journal for Numerical Methods in Biomedical Engineering最新文献

The main objectives of this work are to validate a 1D-0D unsteady solver with a distributed stenosis model for the patient-specific estimation of resting haemodynamic indices and to assess the sensitivity of instantaneous wave-free ratio (iFR) predictions to uncertainties in input parameters. We considered 52 patients with stable coronary artery disease, for which 81 invasive iFR measurements were available. We validated the performance of our solver compared to 3D steady-state and transient results and invasive measurements. Next, we used a polynomial chaos approach to characterise the uncertainty in iFR predictions based on the inputs associated with boundary conditions (coronary flow, compliance and aortic/left ventricular pressures) and vascular geometry (radius). Agreement between iFR and the ratio between cardiac cycle averaged distal and aortic pressure waveforms (resting $P_d/P_a$ ) obtained through 1D-0D and 3D models was satisfactory, with a bias of 0.0-0.005 (±0.016-0.026). The sensitivity analysis showed that iFR estimation is mostly affected by uncertainties in vascular geometry and coronary flow (steady-state parameters). In particular, our 1D-0D method overestimates invasive iFR measurements, with a bias of -0.036 (±0.101), indicating that better flow estimates could significantly improve our modelling pipeline. Conversely, we showed that standard pressure waveforms could be used for simulations, since the impact of uncertainties related to inlet-pressure waveforms on iFR prediction is negligible. Furthermore, while compliance is the most relevant transient parameter, its effect on iFR estimates is negligible compared to that of vascular geometry and flow. Finally, we observed a strong correlation between iFR and resting $P_d/P_a$ , suggesting that steady-state simulations could replace unsteady simulations for iFR prediction.

The intra-aortic balloon pump (IABP) is a widely-used mechanical circulatory support device that enhances hemodynamics in patients with heart conditions. Although the IABP is a common clinical tool, its effectiveness in enhancing outcomes for patients with acute myocardial infarction and cardiogenic shock remains disputed. This study aimed to assess the effectiveness of intra-aortic dual-balloon pump (IADBP) and its impact on aortic hemodynamics compared with an IABP. Three-dimensional finite element models were constructed for the aorta, IABP, and IADBP, followed by numerical simulation using the fluid-structure coupling (FSI) method. Three simulations were conducted: Heart failure patients without assistive devices (Case A), those with IABP (Case B), and those with IADBP (Case C). The study assessed the IADBP's hemodynamic effects by measuring aortic branch blood flow, left ventricular afterload, aortic wall stress, and wall shear stress. IADBP outperformed IABP in enhancing blood flow to the coronary arteries, upper limbs, and brain vessels (left and right coronary arteries: 0.88 vs. 1.27, 1.27 vs. 1.99 mL/beat; brachiocephalic artery, left common carotid artery, and left subclavian artery: 6.08 vs. 12.39, 2.48 vs. 4.97, 2.31 vs. 5.08 mL/beat). IADBP also demonstrated superior performance in counterpulsation pressure and left ventricular ejection (counterpulsation phase: 97.41 mmHg vs. 110.03 mmHg; ventricular unloading phase: 72.21 mmHg vs. 66.46 mmHg). The use of IADBP elevates stress on the aortic wall and wall shear stress, potentially affecting vascular health. IADBP effectively addresses upper limb and cerebral hypoperfusion issues associated with IABP, demonstrating superior performance in enhancing counterpulsation pressure and left ventricular ejection. Despite potential vascular biomechanical effects, IADBP provide a promising clinical treatment option. Further studies are needed to refine IADBP 's design and evaluate its long-term clinical efficacy.

The imaging of the live cochlea is a challenging task. Regardless of the quality of images obtained from modern clinical imaging techniques, the internal structures of the cochlea mainly remain obscured. Electrical impedance tomography (EIT) is a safe, low-cost alternative medical imaging technique with applications in various clinical scenarios. In this article, EIT is investigated as an alternative method to image and extract the centre of gravity of the modiolus in vivo. This information can be used to augment present postoperative medical imaging techniques to investigate the cochlea. The cochlear implant EIT system was simulated by modelling user-specific electrode array trajectories within a simple conductive medium containing an inhomogeneity representing the modiolus. The method included an adapted adjacent stimulation protocol for data collection. For the image reconstruction, NOSER and Tikhonov priors were considered. A parameter analysis was conducted to find the most robust combination of image priors and hyperparameters for this application. The cochlear implant EIT methodology was validated at different noise levels for four electrode array trajectories. Comparing the NOSER and Tikhonov priors, it was observed that the NOSER prior exhibits superior centre of gravity localisation performance in cochlear implant EIT image reconstruction for different noise levels and user-dependent variability in electrode array trajectories. Image reconstruction, using a NOSER prior at a hyperparameter value of approximately 0.001, resulted in an average centre of gravity localisation error of less than 4% for all electrode array trajectories using difference imaging and less than 5.5% using absolute imaging.

The finite-element method (FEM) is a well-established procedure for computing approximate solutions to deterministic engineering problems described by partial differential equations. FEM produces discrete approximations of the solution with a discretisation error that can be quantified with a posteriori error estimates. The practical relevance of error estimates for biomechanics problems, especially for soft tissue where the response is governed by large strains, is rarely addressed. In this contribution, we propose an implementation of a posteriori error estimates targeting a user-defined quantity of interest, using the dual-weighted residual (DWR) technique tailored to biomechanics. The proposed method considers a general setting that encompasses three-dimensional geometries and model nonlinearities, which appear in hyperelastic soft tissues. We take advantage of the automatic differentiation capabilities embedded in modern finite-element software, which allows the error estimates to be computed generically for a large class of models and constitutive laws. First, we validate our methodology using experimental measurements from silicone samples and then illustrate its applicability for patient-specific computations of pressure ulcers on a human heel.

In a previous study [H. Shintaku et al., Sensors and Actuators A: Physical 158 (2010): 183-192], an artificially developed auditory sensor device showed a frequency selectivity in the range from 6.6 to 19.8 kHz in air and from 1.4 to 4.9 kHz in liquid. Furthermore, the sensor succeeded in obtaining auditory brain-stem responses in deafened guinea pigs [T. Inaoka et al., Proceedings of the National Academy of Sciences of the United States of America 108 (2011): 18390-18395]. Since then, several research groups have developed piezoelectric auditory devices that have the capability of acoustic/electric conversion. However, the piezoelectric devices are required to be optimally designed with respect to the frequency range in liquids. In the present study, focusing on the trapezoidal shape of the piezoelectric membrane, the vibration characteristics are numerically and experimentally investigated. In the numerical analysis, solving a three-dimensional fluid-structure interaction problem, resonant frequencies of the trapezoidal membrane are evaluated. Herein, Young's modulus of the membrane, which is made of polyvinylidene difluoride and is different from that of bulk, is properly determined to reproduce the experimental results measured in air. Using the modified elastic modulus for the membrane, the vibration modes and resonant frequencies in liquid are in good agreement with experimental results. It is also found that the resonant characteristics of the artificial basilar membrane for guinea pigs are quantitatively reproduced, considering the fluid-structure interaction. The present numerical method predicts experimental results and is available to improve the frequency selectivity of the piezoelectric membranes for artificial cochlear devices.

As the number of cerebral aneurysms treated with flow diverters continues to increase, it is important to understand what factors influence not only thrombus formation within the aneurysm cavity but also fibrin accumulation across the device and its associated disruption and blockage of the inflow stream. Both processes contribute to the eventual occlusion of the aneurysm or its continued patency and incomplete occlusion which may require future re-treatment. To investigate fibrin accumulation on flow diverters placed across the neck of cerebral aneurysms, a previously developed computational model that couples flow and fibrin dynamics is used in combination with experimental in vitro models of cerebral aneurysms treated with flow diverters. Fibrin accumulation was previously investigated in four glass models of cerebral aneurysms with varying parent artery geometries placed in a flow loop at different flow rates. Corresponding computational models were constructed and compared with the experimental findings. The computational model based on fibrin production stimulated from flow shear stress and subsequent adhesion to device wires was able to reproduce and explain the fibrin accumulation patterns observed in the experimental aneurysms treated with flow diverters. Specifically, these models indicated that increasing vessel curvature, flow rate, and thrombin concentration induced faster fibrin accumulation and associated aneurysm inflow disruption and blockage. The models described and tested in this paper are valuable to understand the detailed mechanisms leading to aneurysm occlusion and healing or incomplete occlusions after treatment with flow diverting devices.

Developing realistic numerical foot models is essential to accurately predict the structural behavior of its bones and soft tissues. The representation of the foot joints is a crucial point that must be considered to recreate these models' natural behavior. Numerically, different types of contact represent these interactions, two being the most common: one that allows movement between bones and one that restricts it. However, the structural behavior of the model is affected depending on which type of contact is chosen to simulate the interaction. Therefore, this paper aims to develop a numerical foot model to analyze and quantify both types of mechanical contact and determine their effect on soft tissues by evaluating and comparing different structural parameters. The results show that the TA, CPF, LPF, EDB, and FDBT soft tissues reach the maximum stress and strain levels like the highest displacement values. The differences between models in these tissues reach percentage values of up to 74.69% for the principal stresses and up to 68.42% for the principal strains. Significant differences were also found in the displacements obtained in the anteroposterior axes (X) and the vertical or the load axis (Y) of up to 42.03% and 37.47%, respectively. These results allow us to quantify the impact that the choice of the contact type of the foot joints has over its soft tissues and suggest that the way of simulating the movement between bones contributes significantly to the quantitative variation of the structural parameters, affecting thus, the predictions made in the several studies performed with foot numerical models; a contact type that reproduces the natural joint movement is the better option based on this work results.

It remains inconclusive about the stability and optimal fixation scheme of screw internal fixation for lateral malleolus oblique fractures in clinical practice. In this study, the effects of different screw internal fixation methods on the biomechanics of lateral malleolus oblique fractures were investigated. These efforts are expected to lay a theoretical foundation for the selection of internal fixation methods and rehabilitation training regimens in the treatment of lateral malleolus fractures. A healthy ankle joint model and a lateral malleolus fracture internal fixation model were established based on CT data with the aid of some software. Besides, the effects of screw internal fixation modalities on the fracture displacement of fibula fractures, fibula Von Mises stress, and screw Von Mises stress under different physiological conditions and loading conditions were investigated using finite element methods (FEMs) and in vitro physical experiments. The double screw vertical fibular axis internal fixation approach had the lowest fracture displacement of fibula fractures and screw Von Mises stress values; while the double screw vertical fracture line internal fixation approach had the lowest fibula Von Mises stress values. Under different physiological conditions, the magnitude of the peak Von Mises stress of the fibula and screw was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 10° > dorsiflexion 20°; and the magnitude of the peak displacement of the fibula fracture breaks was ranked as plantarflexion 20° > plantarflexion 10° > neutral position > dorsiflexion 20° > dorsiflexion 10°. The results of in vitro physical experiments and finite element analyses were in good agreement, which validated the validity of finite element analyses. The vertical fracture line screw implantation method displays a better load-sharing ability; while the vertical fibular axis screw implantation method exhibits a better ability to prevent axial shortening of the fibula and also reduces the risk of screw fatigue damage. Overall, the double screw achieves better therapeutic effects than the single screw. Given that the ankle joint has high stability in the dorsiflexion position, it is recommended to prioritize dorsiflexion rehabilitation training, rather than dorsiflexion and plantarflexion rehabilitation training with too large angles, in the treatment of lateral malleolus fractures.

Transjugular intrahepatic portosystemic shunt (TIPS) is a widely used surgery for portal hypertension. In clinical practice, the diameter of the stent forming a shunt is usually selected empirically, which will influence the postoperative portal pressure. Clinical studies found that inappropriate portal pressure after TIPS is responsible for poor prognosis; however, there is no scheme to predict postoperative portal pressure. Therefore, this study aims to develop a computational model applied to predict the portal pressure after TIPS ahead of the surgery. For this purpose, a patient-specific 0-3-D multi-scale computational model of the hepatic circulation was developed based on preoperative clinical data. The model was validated using the prospectively collected clinical data of 18 patients. Besides, the model of a representative patient was employed in the numerical experiment to further investigate the influences of multiple pathophysiological and surgical factors. Results showed that the difference between the simulated and in vivo measured portal pressures after TIPS was -1.37 ± 3.51 mmHg, and the simulated results were significantly correlated with the in vivo measured results (r = 0.93, p < 0.0001). Numerical experiment revealed that the estimated model parameters and the severity of possible inherent portosystemic collaterals slightly influenced the simulated results, while the shunt diameter considerably influenced the results. In particular, the existence of catheter for pressure measurement would markedly influence postoperative portal pressure. These findings demonstrated that this computational model is a promising tool for predicting postoperative portal pressure, which would guide the selection of stent diameter and promote individualization and precision of TIPS.

Accurate reconstruction of the right heart geometry and motion from time-resolved medical images is crucial for diagnostic enhancement and computational analysis of cardiac blood dynamics. Commonly used segmentation and/or reconstruction techniques, exclusively relying on short-axis cine-MRI, lack precision in critical regions of the right heart, such as the ventricular base and the outflow tract, due to its unique morphology and motion. Furthermore, the reconstruction procedure is time-consuming and necessitates significant manual intervention for generating computational domains. This study introduces an end-to-end hybrid reconstruction method specifically designed for computational simulations. Integrating information from various cine-MRI series (short/long-axis and 2/3/4 chambers views) with minimal user contribution, our method leverages registration- and morphing-based algorithms to accurately reconstruct crucial cardiac features and complete cardiac motion. The reconstructed data enable the creation of patient-specific computational fluid dynamics models, facilitating the analysis of the hemodynamics in healthy and clinically relevant scenarios. We assessed the accuracy of our reconstruction method against ground truth and a standard method. We also evaluated volumetric clinical parameters and compared them with the literature values. The method's adaptability was investigated by reducing the number of cine-MRI views, highlighting its robustness with varying imaging data. Numerical findings supported the reliability of the approach for simulating hemodynamics. Combining registration- and morphing-based algorithms, our method offers accurate reconstructions of the right heart chambers' morphology and motion. These reconstructions can serve as valuable tools as domain and boundary conditions for computational fluid dynamics simulations, ensuring seamless and effective analysis.