大規模蓄電池への応用に向けた亜鉛負極の界面反応プロセスの解析と制御

早大学位記番号:新8189早稲田大

Computational study of kinematics of the anterior cruciate ligament double-bundle structure during passive knee flexion–extension

The anterior cruciate ligament (ACL) comprises an anteromedial bundle (AMB) and posterolateral bundle (PLB). Cadaver studies showed that this double-bundle structure exhibits reciprocal function during passive knee flexion–extension, with the PLB taut in knee extension and the AMB taut in knee flexion. In vivo measurements indicated that straight-line lengths of both bundles decrease with increasing knee-flexion angle (KFA). To interpret these seemingly conflicting facts, we developed a computational ACL model simulating the kinematics of the double-bundle structure during passive knee flexion–extension. Tibial and femoral shapes were reconstructed from computed-tomography images of a cadaver knee and used to construct an idealized model of an ACL including its bundles at the tibiofemoral joint. The ACL deformations at various KFAs were computed by finite element analysis. Results showed that the PLB was stretched in knee extension (KFA = 0∘) and slackened with increasing KFA. The AMB was stretched in knee extension (KFA = 0∘) and remained stretched on the medial side when the knee flexed (KFA = 90∘), but its straight-line length decreased with increasing KFA. These findings are consistent with cadaver and in vivo experimental results and highlight the usefulness of a computational approach for understanding ACL functional anatomy.Otani T., Kobayashi Y., Tanaka M.. Computational study of kinematics of the anterior cruciate ligament double-bundle structure during passive knee flexion–extension. Medical Engineering and Physics, 83, 56-63. https://doi.org/10.1016/j.medengphy.2020.07.015

Computational modelling of ankle-foot orthosis to evaluate spatially asymmetric structural stiffness: Importance of geometric nonlinearity

An ankle-foot orthosis (AFO) constructed as a single piece of isotropic elastic material is a commonly used assistive device that provides stability to the ankle joint of patients with spastic diplegic cerebral palsy. The AFO has asymmetric stiffness that restricts plantarflexion during the swing phase while it is flexible to allow dorsiflexion during the stance phase with a large deflection, including buckling originating from geometric nonlinearity. However, its mechanical implications have not been sufficiently investigated. This study aims to develop a computational model of an AFO considering geometric nonlinearity and examine AFO stiffness asymmetry during plantarflexion and dorsiflexion using physical experiments. Three-dimensional AFO mechanics with geometric nonlinearities were expressed using corotational triangle-element formulations that obeyed Kirchhoff–Love plate theory. Computational load tests for plantarflexion and dorsiflexion, using idealised AFOs with two different ankle-region designs (covering or not covering the apexes of the malleoli), showed that plantarflexion moment–ankle angle relationships were linear and dorsiflexion moment–ankle angle relationships were nonlinear; increases in dorsiflexion led to negative apparent stiffness of the AFO. Both ankle-region designs resisted both plantarflexion and dorsiflexion, and out-of-plane elastic energy was locally concentrated on the lateral side, resulting in large deflections during dorsiflexion. These findings give insight into appropriate AFO design from a mechanical viewpoint by characterising three-dimensional structural asymmetry and geometric nonlinearity.Wataru Sumihira, Tomohiro Otani, Yo Kobayashi, Masao Tanaka, Computational modelling of ankle-foot orthosis to evaluate spatially asymmetric structural stiffness: Importance of geometric nonlinearity, Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine. pp. 9544119221114199. Copyright © 2022 SAGE Publications. DOI: 10.1177/09544119221114199

Performance assessment of displacement-field estimation of the human left atrium from 4D-CT images using the coherent point drift algorithm

Background: Cardiac four-dimensional computed tomography (4D-CT) imaging is a standard approach used to visualize left atrium (LA) deformation for clinical diagnosis. However, the quantitative evaluation of LA deformation from 4D-CT images is still a challenging task. We assess the performance of LA displacement-field estimation from 4D-CT images using the coherent point drift (CPD) algorithm, which is a robust point set alignment method based on the expectation–maximization (EM) algorithm. Method: Subject-specific LA surfaces at 20 phases/cardiac cycles were reconstructed from 4D-CT images and expressed as sets of triangular elements. The LA surface at the phase that maximized the LA surface area was assigned as the control LA surface and those at the other 19 phases were assigned as observed LA surfaces. The LA displacement-field was estimated by solving the alignment between the control and observation LA surfaces using CPD. Results: Global correspondences between the estimated and observed LA surfaces were successfully confirmed by quantitative evaluations using the Dice similarity coefficient and differences of surface area for all phases. The surface distances between the estimated and observed LA surfaces ranged within 2 mm, except at the left atrial appendage and boundaries, where incomplete data, such as missing or false detections, were included on the observed LA surface. We confirmed that the estimated LA surface displacement and its spatial distribution were anisotropic, which is consistent with existing clinical observations. Conclusion: These results highlight that the LA displacement field estimated by CPD robustly tracks global LA surface deformation observed in 4D-CT images

A braided stent becomes flattened inside a curved catheter tube: A micro-CT imaging study

BACKGROUND: The braided stent is a widely accepted endovascular treatment device consisting of woven metal wires. One of the unsolved issues for the braided stent is the stent flattening phenomena when deployed into highly curved arteries. Although a recent computational study highlighted that the mechanical state of the stent inside the catheter before the deployment plays an essential role in causing stent flattening, there is no experimental observation for the stent inside the curved catheter. OBJECTIVE: We investigated braided stent shapes in curved catheter tubes with various curvatures by micro-computed tomography (CT). METHODS: A braided stent was deployed into catheter tubes and set in rectangular cases with constant curvature. The three-dimensional shape of the stent was imaged by micro-CT, and its cross-sectional flatness was quantitatively assessed. RESULTS: Stent flattening occurred in cases of high curvatures of the outer side of the tube curvature, and the degree of flatness increased with increasing tube curvature. This demonstrates that stent flattening can be caused inside the highly curved catheter before deployment. CONCLUSIONS: This preliminary and first observational report provides new insight into the mechanism of stent flattening and emphasizes the importance of the geometrical and mechanical state of the stent inside the catheter.The definitive, peer reviewed and edited version of this article is published in Bio-Medical Materials and Engineering, vol. 31, no. 6, pp. 373-380, 2020, https://doi.org/10.3233/BME-206011

An Eulerian formulation for the computational modeling of phase-contrast MRI

Otani T., Sekine T., Sato Y., et al. An Eulerian formulation for the computational modeling of phase-contrast MRI. Magnetic Resonance in Medicine, (2024); https://doi.org/10.1002/mrm.30302.Purpose: Computational simulation of phase-contrast MRI (PC-MRI) is an attractive way to physically interpret properties and errors in MRI-reconstructed flow velocity fields. Recent studies have developed PC-MRI simulators that solve the Bloch equation, with the magnetization transport being modeled using a Lagrangian approach. Because this method expresses the magnetization as spatial distribution of particles, influences of particle densities and their spatial uniformities on numerical accuracy are well known. This study developed an alternative method for PC-MRI modeling using an Eulerian approach in which the magnetization is expressed as a spatially smooth continuous function. Methods: The magnetization motion was described using the Bloch equation with an advection term and computed on a fixed grid using a finite difference method, and k-space sampling was implemented using the spoiled gradient echo sequence. PC-MRI scans of a fully developed flow in straight and stenosed cylinders were acquired to provide numerical examples. Results: Reconstructed flow in a straight cylinder showed excellent agreement with input velocity profiles and mean errors were less than 0.5% of the maximum velocity. Numerical cases of flow in a stenosed cylinder successfully demonstrated the velocity profiles, with displacement artifacts being dependent on scan parameters and intravoxel dephasing due to flow disturbances. These results were in good agreement with those obtained using the Lagrangian approach with a sufficient particle density. Conclusion: The feasibility of the Eulerian approach to PC-MRI modeling was successfully demonstrated

Shape memory alloy actuated ankle foot orthosis for reduction of locomotion force

peer reviewedHumans can be considered inefficient at walking because they are unable to achieve the theoretically ideal 'zero energy cost' of steady-state locomotion that is possible for bipeds who have elastic tissues. This inefficiency is mainly due to part of the energy that is generated by the body to complete a single step being dissipated instead of being stored for use in the proceeding step. This suggests that we can improve locomotion efficiency and reduce the metabolic energy cost of walking by manipulating the elasticity of the lower limbs using exoskeletal devices [1]. However, most traditional designs use springs made from regular material that have a constant stiffness. These devices exert a linear force pattern that is not biocompatible because they do not mimic the forces of the muscles or the tendons of the human body. This paper presents an interdisciplinary study of the design of a passive-dynamic ankle foot orthosis mechanism that reduces the biological muscle force requirements during locomotion, thus reducing the metabolic energy cost of walking while maintaining biocompatibility. Shape memory alloy is used as a smart material for an actuator owing to its super-elasticity. This super-elasticity provides a nonlinear stiffness pattern that generates forces comparable to those of healthy muscles

A Giant Thymic Cyst Accompanied by Acute Mediastinitis

We encountered a rare case of thymic cyst accompanied by mediastinitis. A 39-year-old Japanese male presented with fever and chest pain. The chest CT revealed a mass composed of a lobular cystic lesion with inflammation, suggesting the onset of mediastinitis. A definitive histological diagnosis was not obtained, and we performed a thymectomy. Pathologically, the thymic cyst was accompanied by multiple cavities, mimicking thymic cysts, caused by the inflammatory abscess. The surrounding adipose tissue showed inflammatory cell infiltrations with chronic fibrosis. These findings indicate that clinicians should be aware that thymic cysts may cause severe mediastinitis

Lung recruitment after cardiac arrest during procurement of atelectatic donor lungs is a protective measure in lung transplantation

Background: Brain-dead donors are susceptible to pulmonary atelectasis (AT). In procurement surgery, lung recruitment under circulatory conditions and cold-flushing for atelectatic donor lungs often provoke graft injury due to the acute blood inflow. We hypothesized that lung recruitment without blood circulation can mitigate graft injury. This study aimed to examine the benefits of lung recruitment subsequent to cardiac arrest using a porcine lung-transplant model. Methods: Thirteen donor pigs were categorized into the non-atelectatic (No-AT) group (n=3) representing a healthy control group; AT-BCR group (n=5), in which AT was reverted by conventional blood-circulated recruitment (BCR); and AT-no-BCR group (n=5), in which AT was reverted by no-BCR following circulatory arrest. In the atelectatic donor models, the left main bronchus was ligated for 24 hours prior to lung procurement. Left lung transplantation (LTx) was subsequently performed in the thirteen recipient pigs. After 6 hours evaluation, the recipients were euthanized and the lung grafts were excised. Results: The post-transplant PaO2/FiO(2) ratio was significantly higher in the AT-no-BCR group than in the AT-BCR group (P=0.015). Wet/dry ratio, histological findings of graft injury and tissue interleukin-8 expression in the AT-no-BCR group were similar to those of the No-AlT group. Conclusions: Lung recruitment without circulation after circulatory arrest could be more protective for atelectatic donor lung than the conventional procedure

CAUSES OF FUNCTIONAL DECLINE IN ELDERLY HOSPITALIZED PATIENTS RECEIVING EITHER INDIVIDUAL OR EXCLUSIVE REHABILITATION THERAPY: A COHORT STUDY

Background: Recently, exclusive rehabilitation therapy was introduced to prevent functional decline due to hospital-associated deconditioning by managing older inpatients’ activities of daily living in Japan. However, this type of therapy does not provide one-on-one exercises similar to individual rehabilitation therapy. This study aimed to report the present ward conditions and the causes of the functional decline in elderly patients receiving individual or exclusive rehabilitation therapy. Methods: A total of 1,636 inpatients, aged 65 years or older, were included in the study. Barthel Index at admission and discharge was assessed prospectively to analyze functional decline. We further analyzed the causes of functional decline by investigating the inpatient’s medical records. Results: Forty-three inpatients (2.6%) had functional decline during hospitalization. There were no significant differences in age, Barthel Index at the time of admission, and the type of clinical department between inpatients with and without functional decline. The functional decline rate in individual rehabilitation therapy was 8.2%, which was significantly higher compared to exclusive rehabilitation therapy (0.8%). The most common causes of functional decline were a pain, low postoperative physical fitness, malignant neoplasm, and new-onset cerebral stroke. Conclusion: We report the present ward conditions in elderly patients receiving either individual or exclusive rehabilitation therapies. Functional decline was correlated to the inpatients’ disease and conditions. The causes of the functional decline can be classified based on whether rehabilitation was effective or ineffective. If the functional decline was caused by hospital-associated deconditioning, we should address the functional decline by providing appropriate rehabilitation methods