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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.

Biomodels, which are models of tissues such as blood vessels, have recently come into high demand for surgical training or medical device assessment use. Since the stiffness of blood vessels is not uniform, reproducing this nonuniformity would be advantageous to producing more realistic models, and to do this, we used a poly (vinyl alcohol) hydrogel (PVA-H) 3D printer. As a material, recently PVA-H has received increasing attention. This printing technique may be suitable for fabricating models composed of parts exhibiting different levels of stiffness (multipart models). However, the PVA-H 3D printer uses outer molds as supports. Outer mold removal as a post-process might affect the mechanical properties of the models or other post-processes such as ethanol substitution, and this requires investigation. Quality checks on the mechanical properties of the final product are also necessary. In this study, the effect of outer molds on the efficiency of ethanol substitution was estimated by measuring specimen weights. Additionally, the effect of the heat generated when molds were removed with an ultrasonic cleaner on the Young’s modulus of models was tested using tensile tests. Moreover, multipart pieces were fabricated, and their mechanical properties were measured. The findings were that ethanol substitution was able to be completed by conventional methods. Furthermore, the heat generation did not change the Young’s modulus of the models. Also, it was possible to fabricate multipart PVA-H models, and their level of stiffness followed the theoretical equation that assumes constant stiffness and independency of each part. The PVA-H 3D printer, therefore, has the potential to fabricate multipart models that will enable better surgical training and device assessments.

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.

Endovascular treatment has become the standard for intracranial aneurysm management. In vitro systems including an artery model are required for devices evaluation and clinician training. Although silicone is usually use for such model, its compliance is known to be lower than blood vessels. The purpose of this study was to analyze the influence of model material compliance on flow properties. Silicone and 12 [wt%] poly (vinyl alcohol) hydrogel (PVA-H) were used to create two box-shaped models of significantly different compliance. The inner lumen geometry was a 4 [mm] diameter straight tube (parent vessel) and a 10 [mm] diameter sphere representing the aneurysm. A blood-mimicking fluid made of a mixture of glycerin, water and sodium iodide was used to reproduce the viscosity and density of blood and fit models refractive index. The circulation system consisted of a pulsatile blood pump and resistance valve. A flow rate of 250±50 [ml/min] and pressure from 75 to 115 [mmHg] were set inside the model. Pressure and flow rate sensors were used to monitor flow conditions before and after the model. Particle image velocimetry (PIV) was performed to record the difference of flow patterns inside the aneurysm of both model using a Nd:YAG solid laser system and fluorescent particles. Results revealed a significant change of flow conditions due to model compliance. Attenuation of the flow rate pulse was recorded between the inlet and the outlet of the both model. This attenuation was 51% for PVA-H model. Moreover, a time lag between outlet pressure and outlet flow rate curves was recorded in both model. This time lag was longer with the PVA-H model, as this model exhibit a greater compliance. PIV experiments revealed significant changes of flow patterns and velocity inside the aneurysm. Because of its high compliance, PVA-H model walls moved under the pulsatile conditions. A change of flow direction and decrease of its velocity were observed near the proximal wall of the aneurysm, compared to the silicone model. Such differences might modify the stress on the wall of the aneurysm. To conclude, our experiments revealed that compliance has significant impacts on flow properties and should be taken into account for in vitro vascular model manufacturing.

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.

Stem cells in the bone marrow (BM) are used as regenerative treatment for leukemia. They are usually harvested by puncturing the cancellous bone in the ilium of the donor with a needle. However, this process can cause severe burden to the donor because of its inefficiency; the bone may require 50–100 punctures to obtain enough stem cells. Various factors affect the volume of BM harvested, and their influence can be estimated by observing the flow in the cancellous bone. Recent computational fluid dynamics (CFD) analyses of BM with 3-D reconstruction of the cancellous bone have profiled flow velocity or wall shear stress (WSS) and have shown that some parts on the surface of the cancellous bone have higher WSS and that this high WSS may tear cells from the surface of the bone. CFD analysis may therefore help determining a method for efficient stem cell harvest. However, it is difficult to validate CFD using BM structure because of its porosity. To improve the accuracy of WSS and flow pattern calculations, blood characteristics should be incorporated as key factors and the effects of non-Newtonian flow and viscosity on the flow patterns evaluated. Therefore, the purpose of this study was to evaluate CFD analyses of BM in the cancellous bone based on flow where viscosity depended on the shear rate. BM from porcine ilium bones was extracted, and the viscosities of samples, with or without anti-clotting medications, were measured at various shear rates. 3-D reconstruction of the cancellous bone was performed using micro-CT after removing BM and fat from the bone. The resolution of the reconstruction was 11.7 μm per pixel, which was sufficient to reconstruct the porous structure. The size of the bone sample was 2.5 × 2.5 × 3.5 mm. The number of mesh was approximately 4.3 million. CFD analyses were performed using 3-D reconstruction and viscosity profile at three pressure differences (5, 7, and 10 kPa). Constant pressure was applied in the outlet. The viscosity of BM could be divided into three shear rate ranges. The first corresponded with a shear rate over 100 1/s, where the viscosity was constant at less than 0.01 Pa·s. Transient curves were observed for shear rates 0.01–100 1/s. At lower shear rates, the viscosity was again constant, at over 105 Pa·s. These changes were higher than the changes in blood viscosity based on the shear rate. The CFD analyses showed that the results depended on the inlet pressure. When the pressure difference was 10 kPa, the viscosity change almost disappeared, and the velocity profile was similar to that of Newtonian flow. When the pressure difference was 5 or 7 kPa, changes in viscosity and completely changed flow patterns were observed. The WSS profile also changed with the velocity profile. Therefore, pressure can be a major factor in the velocity profile of BM in the cancellous bone. Effects of non-Newtonian flow on velocity and WSS profiles were observed under an appropriate pressure difference.

The purpose of this study was to develop a working fluid with the proper viscosity to mimic blood flow to evaluate an ablation catheter. We proposed a working fluid that matches the blood viscosity, using glycerol-saline solution or xanthan gum (XG)-saline solution. We compared the two solution mixtures at various concentrations (for glycerol-saline solution, 10%, 30%, and 50%; for XG-saline solution, 0.10%, 0.11%, 0.12%, and 0.13%) by measuring their temperature dependence on viscosity. To test the developed working fluids, RF ablations were performed with both solutions, and the flow around the catheter during ablation was observed by particle image velocimetry (PIV) method. In addition, to test the efficacy of the solution mixtures, myocardium was observed after it was soaked separately in the two solution mixtures. The viscosity of both kinds of solution mixtures increased at higher concentrations and decreased with increasing temperatures. At 37°C, the viscosities of 50% glycerol-saline solution and 0.11%–0.13% XG-saline solution were 3–4 mPa·s, a value that is similar to the viscosity of blood. The upward flow resulting from heat convection by ablation was observed around the catheter in the PIV analysis using an in vitro model without flow. The solution mixture with the higher viscosity flowed at a lower velocity around the catheter, and the myocardium soaked in 50% glycerol-saline solution shrunk into a black and tough tissue. On the other hand, the myocardium soaked in XG-saline solution showed no change in color or shape. In conclusion, the XG-saline solution is a superior option for evaluating ablation catheters.Copyright © 2016 by ASME

Vascular plaque deformation reduces blood flow, increases arterial embolism risk, and may lead to ischemic stroke. Plaque stiffness varies widely and is an important factor influencing both plaque and parent artery deformation. These geometric changes affect local hemodynamics, which impact plaque initiation influencing disease progression. However, most previous studies used non-elastic stenotic vessel models. For more realistic analysis, we constructed a stenosis model comprising an elastic poly (vinyl alcohol) hydrogel (PVA-H) parent artery and plaque of variable stiffness. Our previous study using this flexible model demonstrated substantial effects of hydrostatic pressure. Here ultrasonography was conducted under changing hydrostatic pressure to measure geometric changes at the narrowest cross section. PVA-H specimens were constructed with the stiffness of a hard lipid core, smooth muscle, and plaque, as estimated by tensile tests using 5, 12, and 15 wt% PVA, respectively. The change in cross-sectional aspect ratio (height/face length) at the narrowest site is largest (∼1.3) for the 5 wt% PVA-H plaque and smallest (∼1.2) for the 12 wt% PVA-H plaque. Stenotic artery deformation depends on both artery and plaque elasticity. Hydrostatic pressure has a substantial effect on both vessel and plaque geometries, which markedly alter blood flow.Copyright © 2016 by ASME

Background and purpose: Recently, the number of endovascular treatments has increased worldwide because of advances in minimally invasive surgery. We considered the effect of reduced flow due to stent implantation and proposed the design of stent strut pattern from the viewpoint of fluid dynamics. We developed an optimized stent strut pattern using a computational fluid dynamics (CFD) system. A classification of cerebral aneurysms was proposed using the aspect ratio (AR) and the stent strut pattern was optimized. The results of optimal stent strut pattern for reduced blood flow speed and wall shear stress were different, and the influence of the AR values was small because there was no dependence on relationship between blood flow and the AR values due to the use of a straight pipe in the parent artery. The classification of blood flow pattern in a cerebral aneurysm must consider the parent artery curves. In this study, we investigated the relationship between the blood flow pattern in cerebral aneurysms and parent artery curves using CFD. Methods: To investigate the influence of blood flow based on the parent artery curve, the parent artery shape was constructed as follows. Patient-specific parent artery shape with a cerebral aneurysm was reconstructed using OsiriX. Center line was extracted using a vascular modeling tool kit. The parent artery shape was reconstructed based on this center line using CAD. The diameter of the parent artery was 4 mm. The cerebral aneurysm shape was a combination of a straight pipe and a half sphere, and the AR value was fixed at 1.0. The cerebral aneurysm position varied from the original position to a 180° rotated position. Tetrahedral numerical mesh was generated with a commercial mesh generator (ICEM CFD 14.0; Ansys Inc.) for the CFD analysis. The numerical blood flow simulation was performed on a supercomputer using the commercial ANSYS FLUENT 6.3 software package and the finite volume method, and a steady flow simulation was performed. Boundary conditions were set for velocity at the inlet, pressure at the outlet, no-slip parent artery, and stent surface. Reynolds numbers at the inlet determined from the mean blood flow speed were 240 and 600. Results and discussion: In this study, we revealed the blood flow pattern in some cerebral aneurysms using CFD. The pattern in a cerebral aneurysm was influenced by the aneurysm direction and parent artery curves. The blood flow pattern in a neck cerebral aneurysm was classified into two types.

Radiofrequency (RF) catheter ablation is a highly effective treatment for many cardiac arrhythmias, especially for tachyarrhythmia. RF energy is introduced through the catheter onto the endocardial surface to destroy the abnormal heart tissue causing the heart rhythm disorder. Many parameters relate to myocardial temperature, such as RF power, tissue contact, and blood flow. Blood flow is an important factor that has a cooling effect on myocardium and affects the final lesion size. Many previous studies have shown that under temperature control, lesion sizes are larger and tissue temperatures rise faster with a high flow rate. If the flow causes a decrease in the temperature of the catheter tip, the generator will increase the power output to maintain the tip at a constant temperature. However, few studies of RF catheter ablation have investigated how ablation affects blood flow. Observation of the flow pattern around the catheter can help to determine the mechanism of the flow effects on the temperature of the catheter tip. The purpose of this study is to observe the flow pattern during ablation using an in-vitro circulation system developed for Particle Image Velocimetry (PIV). We developed an open-channel circulation system to simulate blood flow. The mold for the open-channel was built with acrylic boards for transparency. The working fluid was 0.9% saline, which was used at room temperature (20°C). Instead of animal myocardium, we used a poly (vinyl alcohol) hydrogel (PVA-H), which has mechanical characteristics that approximate those of biological soft tissue, and contact with the PVA-H surface by the catheter is similar to that with myocardium. A 7 Fr catheter with a 4-mm ablation electrode tip was set perpendicular to the PVA-H surface, and the contact weight between the electrode of the catheter and the PVA-H surface was 2.2 gf. To measure the temperature profile in the PVA-H, a K-type thermocouple with the diameter of 0.5 mm was placed at the depth of 2 mm from the surface. The thermocouple tip was always placed on the catheter axis. The flow pattern at the location where the catheter was held was observed by a high speed camera, and the resulting images were analyzed by particle image velocimetry (PIV). The results showed that in the absence of applied flow, convection flow from the electrode is observed in the areas around the catheter. However, under a 1.6 L/min flow rate, convection flow disappears. In conclusion, blood flow could decrease the catheter tip temperature, and the influence of ablation in the flow around the catheter disappeared.Copyright © 2013 by ASME

One of the main factors affecting blood flow conditions in stenotic arteries is plaque geometry. Plaques can be deformed by the internal pressure, and hence plaque behavior varies depending on its stiffness. Blood flow pattern around a plaque is complicated by plaque behavior, and these complications may lead to growth of the plaque itself. Thus, we can say that geometry and mechanical properties of a plaque, and blood flow will affect each other. To understand the relationship between plaque stiffness and flow pattern, flow measurement using elastic models, which mimic the mechanical properties of blood vessels, is required. Flow patterns with steady flows and a range of hydrostatic pressures were observed by particle image velocimetry. The results show that the model is deformed by hydrostatic pressures. Furthermore, flow patterns are also changed as the results of model deformation, especially at reattachment points. Simultaneously, we performed a numerical simulation for finding a critical parameter of the flow patterns. These results show that the reattachment length increases in the model with high stenosis severity and in a vertically oriented parent artery. In conclusion, a parent artery and plaque can deform because of internal pressure, and these deformation will affect blood flow patterns.