Search

BACKGROUND: Inadequate scaffolding performance hinders the clinical application of the biodegradable zinc alloy stents. OBJECTIVE: In this study we propose a novel stent with the tenon-and-mortise structure to improve its scaffolding performance. METHODS: 3D models of stents were established in Pro/E. Based on the biodegradable zinc alloy material and two numerical simulation experiments were performed in ABAQUS. Firstly, the novel stent could be compressed to a small-closed ring by a crimp shell and can form a tenon-and-mortise structure after expanded by a balloon. Finally, 0.35 MPa was applied to the crimp shell to test the scaffolding performance of the novel stent and meanwhile compare it with an ordinary stent. RESULTS: Results showed that the novel stent decreased the recoiling ratio by 70.7% compared with the ordinary stent, indicating the novel structure improved the scaffolding performance of the biodegradable zinc alloy stent. CONCLUSION: This study proposes a novel design that is expected to improve the scaffolding performance of biodegradable stents.

Initiation, growth, and rupture of cerebral aneurysms are caused by hemodynamic factors. It is extensively accepted that the cerebral aneurysm wall is assumed to be rigid using computational fluid dynamics (CFD). Furthermore, fluid-structure interactions have been recently applied for simulation of an elastic cerebral aneurysm model. Herein, we examined cerebral aneurysm hemodynamics in a realistic moving boundary deformation model based on 4-dimensional computed tomographic angiography (4D-CTA) obtained by high time-resolution using numerical simulation. The aneurysm of the realistic moving deformation model based on 4D-CTA at each phase was constructed. The effect of small wall deformation on hemodynamic characteristics might be interested. So, four hemodynamic factors (wall shear stress, wall shear stress divergence, oscillatory shear index and residual residence time) were determined from the numerical simulation, and their behaviors were assessed in the basilar bifurcation aneurysm.

Stent treatment can be used to treat blood vessel stenosis in a less invasive manner, but re-stenosis is a concern. Because a helical-stent configuration has been thought to reduce the amount of intimal hyperplasia, the helical stent is considered clinically effective. The effects of the helical stent on blood flow velocity, however, have not been studied. In this study, we estimated flow velocities before and after helical stenting using time-intensity-curve (TIC) from angiography images and compared them with straight stenting velocities. As a result, in all cases (N = 3), the velocity reduction was less with helical stenting than with straight stenting. Based on angiography images, this flow estimation method can estimate patient-specific blood flow velocity in situ even in a presence of a stent.

IntroductionDespite a decade of research into virtual stent deployment and the post-stenting aneurysmal hemodynamics, the hemodynamic factors which correlate with successful treatment remain inconclusive. We aimed to examine the differences in various post-treatment hemodynamic parameters between successfully and unsuccessfully treated cases, and to quantify the additional flow diversion achievable through stent compaction or insertion of a second stent.MethodsA systematic review and meta-analysis were performed on eligible studies published from 2000 to 2019. We first classified cases according to treatment success (aneurysm occlusion) and then calculated the pooled standardized mean differences (SMD) of each available parameter to examine their association with clinical outcomes. Any additional flow diversion arising from the two common strategies for improving the stent wire density was quantified by pooling the results of such studies.ResultsWe found that differences in the aneurysmal inflow rate (SMD −6.05, 95% CI −10.87 to −1.23, p=0.01) and energy loss (SMD −5.28, 95% CI −7.09 to −3.46, pConclusionsInflow rate and energy loss have shown promise as identifiers to discriminate between successful and unsuccessful treatment, pending future research into their diagnostic performance to establish optimal cut-off values.

An existence probability atlas has been used for automatic labeling of cerebral arteries. However, the number of arteries varies frequently because of image quality and individual variation of the artery structure. To moderate the influence of number imbalance on labeling accuracy, we propose a new normalized atlas for automatic labeling of cerebral artery centerlines. The number of arteries, which was obtained from magnetic resonance angiography, varies from 11 to 46 among the artery sites. Based on the centerline and diameter, the arterial volume was reconstructed into a voxel space for each subject. After superimposing arteries from 46 subjects, three normalization methods were compared: dividing by the number of subjects (N), by N and the arterial length (L), and by N and the arterial volume (V). To compare the labeling accuracy and precision, the summation of probability and labeling method was also used. The accuracy of all normalization methods was > 85% in all arteries. The precision improved in some parts, with the atlas normalized by N-L and by N-V. The use of N-L and N-V changed the relative value of the existence probability among the parts. Consequently, some normalization methods changed the tendency toward misclassification, which changed the precision.

Thermal ablation has attracted attention as a minimally invasive tissue ablation treatment. Steam flow was recently introduced as a novel ablation procedure. This work aimed to assess the applicability of pulsated steam flow for tumor ablation. Ex vivo ablation was performed using liver, muscle, and fat tissues of sheep. Three experimental protocols of pulse number were administered to these tissues, while computational simulation was conducted according to the ex vivo tests for each tissue. Real-time measurements of temperature revealed heat propagation during and subsequent to ablation. The peak temperature was achieved after ablation. The time to reach the peak (highest temperature) increased with the distance from the thermal sensor to the steam needle according to thermal conductivity, except for steam leakage along to gap between the tissue and blood vessel. A cross-section of the ablated specimen clearly revealed the boundaries of cell defects. The ablated area was droplet shaped up to the steam needle. Computational simulations revealed that the ablated area was consistent with the area with the highest temperature. Though several limitations still remain such as no blood circulation, pulsated steam flow can ablate diverse animal tissues.

Pulse wave has been considered as a message carrier in the cardiovascular system (CVS), capable of inferring CVS conditions while diagnosing cardiovascular diseases (CVDs). Clarification and prediction of cardiovascular function by means of powerful feature-abstraction capability of machine learning method based on pulse wave is of great clinical significance in health monitoring and CVDs diagnosis, which remains poorly studied.Here we propose a machine learning (ML)-based strategy aiming to achieve a fast and accurate prediction of three cardiovascular function parameters based on a 412-subject database of pulse waves. We proposed and optimized an ML-based model with multi-layered, fully connected network while building up two high-quality pulse wave datasets comprising a healthy-subject group and a CVD-subject group to predict arterial compliance (AC), total peripheral resistance (TPR), and stroke volume (SV), which are essential messengers in monitoring CVS conditions.Our ML model is validated through consistency analysis of the ML-predicted three cardiovascular function parameters with clinical measurements and is proven through error analysis to have capability of achieving a high-accurate prediction on TPR and SV for both healthy-subject group (accuracy: 85.3%, 86.9%) and CVD-subject group (accuracy: 88.3%, 89.2%).The independent sample t-test proved that our subject groups could represent the typical physiological characteristics of the corresponding population. While we have more subjects in our datasets rather than previous studies after strict data screening, the proposed ML-based strategy needs to be further improved to achieve a disease-specific prediction of heart failure and other CVDs through training with larger datasets and clinical measurements.Our study points to the feasibility and potential of the pulse wave-based prediction of physiological and pathological CVS conditions in clinical application.

The behavior of wall shear stress (WSS) was previously reported in a deformable aneurysm model using fluid-structure interactions. However, these findings have not been validated. In the present study, we examined the effect of elasticity (i.e., deformation) on wall shear stress inside a cerebral aneurysm at the apex of a bifurcation using particle image velocimetry in vitro. The flow model simulated a human patient-specific aneurysm at the apex of the bifurcation of the middle cerebral artery. Flow characteristics by wall elasticity were examined for both elastic and non-deformable aneurysm models with pulsatile blood flow. The absolute temporally- and spatially-averaged WSS along the bleb wall was smaller in the elastic model than that in the non-deformable model. This small WSS may be related to attenuation of the WSS. Further, the WSS gradient had a finite value near the stagnation point of the aneurysm dome. Finally, the WSS gradient near the stagnation point was slightly smaller in the elastic model than that in the non-deformable model. These data suggest that elasticity of the aneurysm wall can affect the progression and rupture of aneurysms via hemodynamic stress.

Incomplete stent expansion (IncSE) is occasionally seen in flow-diversion (FD) treatment of intracranial aneurysms; however, its haemodynamic consequences remain inconclusive. Through a parametric study, we quantify the aneurysmal haemodynamics subject to different severities of IncSE occurring in different portions of the stent. Two patient cases with IncSE confirmed in vivo were studied. To investigate a wider variety of IncSE scenarios, we modelled IncSE at two severity levels respectively located in the proximal, central, or distal segment of a stent, yielding a total of 14 treatment scenarios (including the ideal deployment). We examined stent wire configurations in 14 scenarios and resolved aneurysm haemodynamics through computational fluid dynamics (CFD). A considerable degradation of aneurysm flow-reduction performance was observed when central or distal IncSE occurred, with the maximal elevations of the inflow rate (IR) and energy loss (EL) being 10% and 15%. The underlying mechanism might be the increased resistance for flow to remain within the FD stent, which forces more blood to leak into the aneurysm sac. Counter-intuitively, a slight reduction of aneurysm inflow was associated with proximal IncSE, with the maximal further reduction of the IR and EL being 5% and 8%. This may be due to the disruption of the predominant parent-artery flow by the collapsed wires, which decreased the strength and altered the direction of aneurysmal inflow. The effects of IncSE vary greatly with the location of occurrence, revealing the importance of performing individualised, patient-specific risk assessment before treatment.

Objectives The purpose of this study was to identify elements that cancer peer supporters working in Japanese hospitals consider to be important in helping them perform their role.Methods A qualitative inductive research was conducted. Introductions to potential participants were obtained from a patient association that agreed to help with the study. Interviews were conducted from July through October 2014, using an interview guide, with cancer peer supporters who consented to participate in the study. Elements they perceived as important to the performance of their role were inductively identified from interview transcripts. The analysis consisted of coding phrases in the text and organizing the codes generated into categories and subcategories.Results The study participants consisted of 10 cancer peer supporters (2 men, 8 women), in the age range of 40 to 70 years, who provided private counseling and worked in cancer support groups in hospitals. The analysis generated 129 codes, 11 subcategories, and 5 categories. These 5 categories were: [1.Help service users determine their own paths by listening to and accepting what they say with a non-judgmental attitude]; [2.Offer a perspective distinct from that of the medical staff]; [3.Think of ways to achieve a good balance between one's personal life and cancer peer support work while maintaining a stable state of mind]; [4.Ensure that one maintains the necessary knowledge and skills, and continually improve oneself]; and [5.Build relationships of trust with medical staff and the hospital].Conclusion Category [1] and category [2] were behaviors regarded as important when interacting with users. They were "matters regarded as important during the practice of cancer peer support working for users," and comprised the core of matters that were regarded as important. Next, as for matters regarded as important in relation to the supporters themselves, the categories were [3] and [4]. These were "matters regarded as important for continuity and qualitative improvement of cancer peer support working." Areas that call for improvement in relation to this are preparation of support systems and learning environments. Another matter regarded as important was category [5]. This was a "matter regarded as important to smoothen and facilitate cancer peer support working." Placing importance on relationships of trust with medical staff and hospitals could be considered a distinctive characteristic of cancer peer supporters working at hospitals.

Coronary artery bypass grafts (CABGs), including saphenous vein grafts (SVGs) or left internal mammary artery (LIMA) grafts, are recently applied to treat coronary artery aneurysm (CAA). Surgical outcomes are considered to be related to surgical strategies (types of the bypass graft and whether CAA ligated or not) and the size of the CAA (usually characterized by diameter). However, the understanding of the relationship between the surgical outcomes and the abovementioned factors is limited. Previous studies related to CABG treatments have shown hemodynamic studies could help evaluate surgical outcomes through graft mass flow rate, wall shear stress (WSS), and oscillatory shear index (OSI). It is believed that the hemodynamic study of applying CABGs to CAA, which is not studied yet, could help us understand the different CABG surgeries. The aim of the study was to evaluate the hemodynamic differences among different surgical methods. To do this, eight three-dimensional models were constructed, representing application of SVGs and LIMA grafts to CAAs (whether ligated or not) with diameters two, three, and five times the normal diameter, to perform computational fluid dynamics (CFD) simulation. The lumped-parameter model (LPM) was coupled to the boundary of the 3D models which increase the complexity of the simulation, but it can ensure the stability of the simulation boundary conditions. The results show that SVG (no matter whether ligated or not) hemodynamic characteristics are positive, with an average high graft mass flow rate of 70 ml/min, an average WSS of 0.479 Pa, and a low OSI of 0.001. LIMA with CAA ligation has the same characteristics with higher WSS (average 1.701 Pa). The hemodynamic characteristics of LIMA without CAA ligation are negative, including high reverse mass flow rate and high OSI (0.367). The results indicate that the surgical outcomes of LIMA with CAA ligation are likely to be the best among these models. The surgical outcomes of LIMA without CAA ligation seem to be undesirable due to the high reverse mass flow and high OSI. The CAA diameter may not have a significant effect on surgical outcomes.

The clinical treatment planning of coronary heart disease requires hemodynamic parameters to provide proper guidance. Computational fluid dynamics (CFD) is gradually used in the simulation of cardiovascular hemodynamics. However, for the patient-specific model, the complex operation and high computational cost of CFD hinder its clinical application. To deal with these problems, we develop cardiovascular hemodynamic point datasets and a dual sampling channel deep learning network, which can analyze and reproduce the relationship between the cardiovascular geometry and internal hemodynamics. The statistical analysis shows that the hemodynamic prediction results of deep learning are in agreement with the conventional CFD method, but the calculation time is reduced 600-fold. In terms of over 2 million nodes, prediction accuracy of around 90%, computational efficiency to predict cardiovascular hemodynamics within 1 second, and universality for evaluating complex arterial system, our deep learning method can meet the needs of most situations., Anzai et al. propose a deep learning approach to estimate the 3D hemodynamics of complex aorta-coronary artery geometry in the context of coronary artery bypass surgery. Their method reduces the calculation time 600-fold, while allowing high resolution and similar accuracy as traditional computational fluid dynamics (CFD) method.

Coronary artery aneurysms (CAAs) have been reported to associate with an increased risk for thrombosis. Distinct to the brain aneurysm, which can cause a rupture, CAA’s threat is more about its potential to induce thrombosis, leading to myocardial infarction. Case reports suggest that thrombosis risk varied with the different CAA diameters and hemodynamics effects (usually wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time (RRT)) may relate to the thrombosis risk. However, currently, due to the rareness of the disease, there is limited knowledge of the hemodynamics effects of CAA. The aim of the study was to estimate the relationship between hemodynamic effects and different diameters of CAAs. Computational fluid dynamics (CFD) provides a noninvasive means of hemodynamic research. Four three-dimensional models were constructed, representing coronary arteries with a normal diameter (1x) and CAAs with diameters two (2x), three (3x), and five times (5x) that of the normal diameter. A lumped parameter model (LPM) which can capture the feature of coronary blood flow supplied the boundary conditions. WSS in the aneurysm decreased 97.7% apparently from 3.51 Pa (1x) to 0.08 Pa (5x). OSI and RRT in the aneurysm were increased apparently by two orders of magnitude from 0.01 (1x) to 0.30 (5x), and from 0.38 Pa−1 (1x) to 51.59 Pa−1 (5x), separately. Changes in the local volume of the CAA resulted in dramatic changes in local hemodynamic parameters. The findings demonstrated that thrombosis risk increased with increasing diameter and was strongly exacerbated at larger diameters of CAA. The 2x model exhibited the lowest thrombosis risk among the models, suggesting the low-damage (medication) treatment may work. High-damage (surgery) treatment may need to be considered when CAA diameter is 3 times or higher. This diameter classification method may be a good example for constructing a more complex hemodynamic-based risk stratification method and could support clinical decision-making in the assessment of CAA.

Background Blood vessels are constantly exposed to flow-induced stresses, and endothelial cells (ECs) respond to these stresses in various ways. Objective In order to facilitate endothelialization after endovascular implantation, cell behaviors around a metallic wire using a flow circulation system are observed. Methods A parallel flow chamber was designed to reproduce constant shear stresses (SSs) on cell surfaces and to examine the effects of a straight bare metal wire on cell monolayers. Cells were then exposed to flow for 24 h under SS conditions of 1, 2, and 3 Pa. Subsequently, cell distributions were observed on the plate of the flow chamber and on the surface of the bare metal wire. Flow fields inside the flow chamber were analyzed using computational fluid dynamics under each SS condition. Results After 24 h, ECs on the bottom plate were concentrated toward the area of flow reattachment. The matching of higher cell density and CFD result suggests that flow-induced stimuli have an influence on EC distributions. Conclusion Typical cell concentration occurs on dish plate along the vortexes, which produces large changes in SSs on cell layer.

Owing to the diversity of pulse-wave morphology, pulse-based diagnosis is difficult, especially pulse-wave-pattern classification (PWPC). A powerful method for PWPC is a convolutional neural network (CNN). It outperforms conventional methods in pattern classification due to extracting informative abstraction and features. For previous PWPC criteria, the relationship between pulse and disease types is not clear. In order to improve the clinical practicability, there is a need for a CNN model to find the one-to-one correspondence between pulse pattern and disease categories. In this study, five cardiovascular diseases (CVD) and complications were extracted from medical records as classification criteria to build pulse data set 1. Four physiological parameters closely related to the selected diseases were also extracted as classification criteria to build data set 2. An optimized CNN model with stronger feature extraction capability for pulse signals was proposed, which achieved PWPC with 95% accuracy in data set 1 and 89% accuracy in data set 2. It demonstrated that pulse waves are the result of multiple physiological parameters. There are limitations when using a single physiological parameter to characterise the overall pulse pattern. The proposed CNN model can achieve high accuracy of PWPC while using CVD and complication categories as classification criteria.

The stent geometrical design (e.g., inter-strut gap, length, and strut cross-section) is responsible for stent-vessel contact problems and changes in the blood flow. These changes are crucial for causing some intravascular abnormalities such as vessel wall injury and restenosis. Therefore, structural optimization of stent design is necessary to find the optimal stent geometry design. In this study, we performed a multiobjective stent optimization for minimization of average stress and low wall shear stress ratio while considering the wall deformation in 3D flow simulations of triangular and rectangular struts. Surrogate-based optimization with Kriging method and expected hypervolume improvement (EHVI) are performed to construct the surrogate model map and find the best configuration of inter-strut gap (G) and side length (SL). In light of the results, G-SL configurations of 2.81-0.39 and 3.00-0.43 mm are suggested as the best configuration for rectangular and triangular struts, respectively. Moreover, considering the surrogate model and flow pattern conditions, we concluded that triangular struts work better to improve the intravascular hemodynamics. ᅟ Graphical abstract.

Vertebrobasilar atherosclerosis is an arterial disease; without successful treatment, it has a mortality rate approximately 80%–95%. Thus, predicting risk factors of vertebrobasilar atherosclerosis is of utmost importance. Previous studies have demonstrated that wall shear stress (WSS) contributes to atherosclerosis. In addition, geometry and WSS are correlated. The present study focuses on the description of equation using detailed relationship between arterial geometry and WSS in the vertebrobasilar system (VBS); magnetic resonance (MR) imaging with computational fluid dynamics (CFD) was used for the analysis. Using constructed patient-specific models, WSS of basilar arteries (BAs) was calculated and then analyzed with morphological parameters. According to the statistical results, both the area and curvature of BAs are associated with WSS. Based on the relations, a liner fitted equation can be proposed. As this study is underway, more precise evaluation of the correlation between morphology and fluid shear stress could help predict risk factors and select treatment methods for this arterial disease.

Rupture of cerebral aneurysms is the main cause of subarachnoid hemorrhage, which can have devastating effects on quality of life. The identification and assessment of unruptured aneurysms from medical images is therefore of significant clinical relevance. In recent years, the availability of clinical imaging data has rapidly increased, which calls for computer assisted detection (CAD) systems. Previous studies have shown that CAD systems based on convolutional neural networks (CNN) can help to detect cerebral aneurysms from magnetic resonance angiographies (MRAs). However, these CAD systems require large datasets of annotated medical images. Thus, more efficient tools for processing and categorizing medical imaging data are required. Previous studies of CNN-based classification for medical images used various patch configurations of input data. These studies showed that classification accuracy was affected by the patch size or image representation. Thus, we hypothesize that the accuracy of CADs to detect cerebral aneurysms can be improved by adjusting the configuration of the input patches. In the present study, we performed CNN-based medical imaging classification for varying input data configurations to examine the relationship between classification accuracy and data configuration.

Objectives This research aims to ascertain the kinds of support cancer peer supporters at medical institutions currently receive and the support they actually need.Methods Participants in the study were ten cancer peer supporters who were recommended by a patient association and who agreed to participate in the study. Using a qualitative descriptive method, interviews were conducted using an interview guide from July to October 2014. Codes were extracted from the interview transcript and divided into categories and subcategories. Accuracy was ensured by checking the data with the participants. The study was conducted with the approval of the Ethics Committee of Mejiro University.Results Research participants consisted of two men and eight women aged forty to seventy years, who were private counselors, telephone counselors, or members of cancer salons at hospitals. Four categories were generated on the basis of the support that cancer peer supporters are currently receiving: mutual learning and support among peer supporters, learning and encouragement from patients, self-improvement in peer supporters, and cooperation with hospitals and the government. Seven categories were generated on the basis of the support that cancer peer supporters need: opportunities for peer supporters to learn from and support each other, further studies on cancer peer support, reliable and up-to-date information, society's understanding and cooperation regarding cancer, financial support for support activities and patient associations, improvement of cancer peer support system, and quality assurance of peer supporter training courses.Conclusion Cancer peer supporters were supporting each other, gaining encouragement from patients, improving themselves, and gaining support from others. However, they also needed additional assistance such as opportunities for supporters to learn from and support each other and reliable and up-to-date information. Moreover, peer supporters needed advice and emotional support from hospital staff as they experienced difficulties during consultation. Various other types of support were needed, such as society's understanding and cooperation regarding cancer, financial support for support activities and patient associations, institutionalization of peer supporter placement in hospitals, and quality assurance of peer supporter training courses. Overall, support for cancer peer supporters is still not sufficient; thus, further help is necessary.

Stent deployment is currently used for many cardiovascular treatments. During its application, the presence of the stent inside the blood vessel will indeed cause some change in both flow environment and also vessel wall's cellular conditions. This research intends to learn about the flow phenomenon of how vessel wall endothelial cells (ECs) react to the presence of stent wires within a microfluidic flow chamber environment. Computational fluid dynamics (CFD) simulation analysis of the microfluidic flow chamber system has been performed for observing the hemodynamics phenomena in the chamber. Moreover, CFD method also can be beneficial as a planning step for a successful experimental study. We found that under the two wires configurations, high wall shear stress (WSS) area is developed on the downstream side of the wires. Based on the analysis of WSS and WSS gradients (WSSG) conditions, ECs morphological change and migration are likely to occur some specific area.

The effect of a simple bare-metal stent on suppression of wall shear stress inside a spherical intracranial aneurysm model was experimentally investigated by two dimensional particle image velocimetry in vitro . The flow model simulated an intracranial aneurysm induced both at the side wall and at the apex of bifurcation between the anterior cerebral artery and the anterior communicating artery. Wall shear stress was investigated using both stented and non-stented models to assess the simple bare metal stent characteristics. The flow behavior inside the stented aneurysm sac was unusual and wall shear stress was much smaller inside the aneurysm sac. For both models, the maximum and the temporal and spatial averaged wall shear stress in the stented model is reduced by at least 50 % from those in the non-stented model. Stent placement effectively suppresses the temporal and spatial variations, and the magnitude of wall shear stress. Consequently, there is an effective possibility that would retard the progress of cerebral aneurysms by even simple stent.

Endovascular stent has been employed to treat patients with intravascular diseases. Research on stent optimization is currently performed in order to find the best design in increasing the treatment efficacy. In this research, stent optimization is performed based on a finite element analysis method via Kriging surrogate model to observe the wall shear stress (WSS) conditions on the strut vicinity. Two configurations, rectangle and triangle are adopted as the cross section of a stent strut and compared to see the effects of the cross section on WSS condition. Strut gap in the range from 1 mm to 3 mm and the strut size length from 0.05 mm to 0.45 mm are considered as the design variables for each cross section. Structure contact simulation between stent and vessel wall is carried out to obtain the 5% vessel expansion. Afterward, computational fluid dynamics simulation is performed to analyze the hemodynamic effect of stent design along with wall deformation. Minimizing the percentage of low WSS area (WSS < 1 Pa) relative to the length of stent deployment area is set as the objective function of this optimization since low WSS is believed to promote some problems such as atherosclerosis. In total, 45 and 42 simulation iterations are conducted respectively for both cross sections to develop the Kriging surrogate models for efficient global optimization. Besides the prediction of the optimized configuration, broader observation on its behavior within the design range is also well predicted. The optimized configuration has 2.99 mm gap and 0.1 mm width for the rectangular strut, and 2.00 mm gap and 0.99 mm width for the triangular strut. The triangular strut has better performance in reducing the low WSS area with 14.6% of low WSS area on its optimized design, compared to 18.3% of the rectangular strut. Moreover, the triangular shape strut produces more stable performance; most design configuration with the strut width of less than 0.35 mm can keep low WSS area at the minimum value.

Background Optimal design of stents for a cerebral aneurysm is desired for efficient flow reduction in the aneurysm. Objective In this study, we aimed to optimize stent design at several porosities, estimate the influence of stent design on aneurysm flow, and evaluate the ability of stents to reduce flow. Methods Stent models were constructed as sets of squares or rectangles in the necks of a two-dimensional (2D) and realistic aneurysm. Then, automated optimization was performed using a combination of simulated annealing and lattice Boltzmann flow simulation. Results By simulated annealing, stents were gradually modified to reduce the average velocity in an aneurysm. As a result of optimization, stents of all porosities demonstrated an inhomogeneous distribution with dense struts in the inflow area. Flow reduction was increased compared with the initial stent. Under the condition of high porosity, flow reduction by the stent drastically increased as porosity decreased. Under low porosity, the increase of velocity reduction was moderate even as porosity decreased. Conclusions Optimization can enhance flow reduction by stents. However, the increase in reduction associated with decreasing porosity is moderate under lower-porosity conditions. This threshold may help in the choice of stent porosity for each specific aneurysm.

【For engineers, generating a mesh in porous media (PMs) sometimes represents a smaller computational load than generating realistic stent geometries with computer fluid dynamics (CFD). For this reason, PMs have recently become attractive to mimic flow-diverter stents (FDs), which are used to treat intracranial aneurysms. PMs function by introducing a hydraulic resistance using Darcy's law; therefore, the pressure drop may be computed by test sections parallel and perpendicular to the main flow direction. However, in previous studies, the pressure drop parallel to the flow may have depended on the width of the gap between the stent and the wall of the test section. Furthermore, the influence of parameters such as the test section geometry and the distance over which the pressure drops was not clear. Given these problems, computing the pressure drop parallel to the flow becomes extremely difficult. The aim of the present study is to resolve this lack of information for stent modeling using PM and to compute the pressure drop using several methods to estimate the influence of the relevant parameters. To determine the pressure drop as a function of distance, an FD was placed parallel and perpendicular to the flow in test sections with rectangular geometries. The inclined angle method was employed to extrapolate the flow patterns in the parallel direction. A similar approach was applied with a cylindrical geometry to estimate loss due to pipe friction. Additionally, the pressure drops were computed by using CFD. To determine if the balance of pressure drops (parallel vs perpendicular) affects flow patterns, we calculated the flow patterns for an ideal aneurysm using PMs with various ratios of parallel pressure drop to perpendicular pressure drop. The results show that pressure drop in the parallel direction depends on test section. The PM thickness and the ratio of parallel permeability to perpendicular permeability affect the flow pattern in an ideal aneurysm. Based on the permeability ratio and the flow patterns, the pressure drop in the parallel direction can be determined.】

Cancellous bone contains bone marrow where hematopoietic stem cells (HSCs) are produced. Those cells represent an interest in the treatment of leukemia during which transplantation of bone marrow is performed to replace patient degraded cells. HSCs are usually harvested by a puncture in the cancellous bone of the donor’s ilium using a needle. However, this procedure can cause severe burden to the donor because of its high invasiveness. The flow of bone marrow is strongly related to the harvesting of HSCs and permeability is one of the major parameters to characterize cancellous bone. Previous researches have already shown an anisotropy of permeability in femur, whereas punctures are usually performed in the iliac cancellous bone. The objective of this paper is to characterize the anisotropic permeability of iliac cancellous bone. Digital images of a porcine iliac cancellous bone sample were obtained by micro-computed tomography (micro-CT), and three locations were selected to fabricate bone models, reproduced by 3D printing at three times magnification. To compare the structure of manufactured models, porosity and its variations along X, Y and Z direction were evaluated from micro-CT images. To measure permeability, a specific perfusion system was developed. The pressure drop between the upstream and the downstream of bone models were measured at different flow rates, reaching a Reynolds number of 27–158, appropriate for the aspiration condition. Darcy-Forchheimer’s law was then applied to calculate the permeability and Forchheimer coefficient of bone models. Results revealed different porosities and resultant permeabilities for each bone nodels. A positive correlation links those two parameters. Different fluctuations of porosity were evaluated along each direction although no significant difference of average porosity was observed. On the other hand, different permeabilities and Forchheimer coefficients were measured in each direction with various degrees of anisotropy. Permeabilities in three orthogonal directions of the model ranged from 1.96 × 10−10 to 4.29 × 10−10 m2. Results indicate that transport properties in cancellous bone depend on the flow directions. The anisotropy of permeability can be used for evaluation of flow in cancellous bone.

Human blood flow is naturally working as a pulsatile flow under the influence of heartbeat cycle. As many blood flow simulation studies have been conducted recently, many assumption and simplification of intravascular flow phenomena were used as the boundary condition of the simulation. For example, stent contact rigid wall condition, steady blood flow also material simple models and properties of tissues and blood. However, these simplifications may lead to inaccuracy of the results and analysis. This paper tries to observe the simulation results from different boundary conditions which include the pulsatile flow conditions and how it behaves compared to the steady flow. From the investigation and comparison, the difference between results of flow parameters obtained from the pulsatile and steady simulation shows 2.2% deviation on the appearance of low WSS along the deployment area.

The cardiovascular stent is one of the medical devices which has been commonly used for curing many vascular diseases. Nowadays, research on many aspects of stent development has been conducted to improve the device's efficacy. Mechanical and flow dynamics analysis on stent performance are useful to understand the impact of the device deployment. Many assumptions have been applied for constructing the stent simulation model including the blood vessel wall condition and its inlet flow conditions. Recently, common assumptions of the stent simulation model are mainly worked under the assumption of rigid wall condition and steady or pulsatile inlet flow. These different assumptions may lead to different simulation results. These differences may also affect the further analysis such as optimization process. This research tries to investigate the pulsatile effect on the stent optimization results based on computational simulation with wall deformation. Comparison with the previous optimization with a steady flow was conducted to find out about the differences between the two conditions. We found that the difference in optimization results from both inflow conditions is insignificant.

Nihon Koshu Eisei Zasshi(JAPANESE JOURNAL OF PUBLIC HEALTH), Vol. 63 (2016) No. 11 p. 664-674: p668(Table 2).

Stent insertion for cerebral aneurysm has been studied using ideal and realistic aneurysms in recent years. Stent insertion aims at reducing the flow in an aneurysm. To minimize the average velocity in an aneurysm, we applied optimization to the strut position in a realistic aneurysm based on computational fluid dynamics. The result shows the effect on velocity reduction of strut placement in the inflow area.

Objectives This study was conducted to develop a scale for measuring "attachment to the local community" for its use in health services. The scale is also intended to nurture new social relationships in late middle-aged individuals.Methods Thirty items were initially planned to be included in the scale to measure "attachment to the local community", according to a previous study that identified the concept. The study subjects were late middle-aged residents of City B in Prefecture A, located in Tokyo suburbs. From the basic resident register data, 1,000 individuals (local residents in the 50-69 year age group) were selected by a multi-stage random sampling technique, on the basis of their residential area, age, and sex (while maintaining the male to female ratio). An unsigned self-administered questionnaire was distributed to the subjects, and the responses were collected by postal mail. The collected data was analyzed using psychometric study of scale.Results Valid responses were obtained from 583 subjects, and the response rate was 58.3%. In an item analysis, none of the items were rejected. In a subsequent factor analysis, 7 items were eliminated. These items included 2 items with a factor loading of0.40, 3 items loading on multiple factors and showing a factor loading of ≥0.40, and 2 items with a low factor correlation (0.04-0.16). These items included factors that related to only these 2 items. Consequently, 23 items in the following 4-factor structure were selected as the scale items: "Source of vitality to live life," "Intention to cherish ties with people," "Place where one can be oneself," and "Pride of being a resident." Cronbach's coefficient α for the entire scale of "attachment to the local community" was 0.95, demonstrating internal consistency. We then examined the correlation with an existing scale to measure social support; the results revealed a statistically significant correlation and confirmed criterion-related validity (P0.001). In addition, the fit indices in a covariance structure analysis showed adequate values.Conclusions The developed scale was considered reliable and appropriate for measuring "attachment to the local community."