193 拍動に伴う血管形状の変形を考慮した2次元超音波計測融合血流解析 : Bモード画像による非定常血管形状抽出

The aim of this study is to elucidate the relation of the inelastic expansive deformation of natural blood vessel and the degradation of elasticity to the time pattern of circulating pulsatile pressure flow. When pulsatile pressure amplitude (delta P = Pmax - Pmin) becomes smaller due to Pmin increasing, the blood vessel is subject to creep deformation. In this sense, pulsating pressure will play a role in avoiding creep effect. Fluctuation of maximum pressure Pmax will induce the increase of inelastic deformation and the decrease of rigidity of the blood vessel. The inelastic deformation and the decrease of rigidity in blood vessel is induced at the stage of pressure amplitude rising from a lower one to a higher, but not during pressure amplitude (delta P) kept constant nor at the pressure amplitude decreasing stage. In order to reduce the degradation of mechanical properties of blood vessel, it may be effective to avoid the increase of Pmin and the variability of Pmax.

In vivo, blood vessels constitutively experience mechanical stresses exerted by adjacent tissues and other structural elements. Vascular collapse, a structural failure of vascular tissues, may stem from any number of possible compressive forces ranging from injury to tumor growth and can promote inflammation. In particular, endothelial cells are continuously exposed to varying mechanical stimuli, internally and externally, resulting in blood vessel deformation and injury. This study proposed a method to model biomechanical-stimuli-induced blood vessel compression in vitro within a polydimethylsiloxane (PDMS) microfluidic 3D microvascular tissue culture platform with an integrated pneumatically actuated compression mechanism. 3D microvascular tissues were cultured within the device. Histological reactions to compressive forces were quantified and shown to be the following: live/dead assays indicated the presence of a microvascular dead zone within high-stress regions and reactive oxygen species (ROS) quantification exhibited a stress-dependent increase. Fluorescein isothiocyanate (FITC)-dextran flow assays showed that compressed vessels developed structural failures and increased leakiness; finite element analysis (FEA) corroborated the experimental data, indicating that the suggested model of vascular tissue deformation and stress distribution was conceptually sound. As such, this study provides a powerful and accessible in vitro method of modeling microphysiological reactions of microvascular tissues to compressive stress, paving the way for further studies into vascular failure as a result of external stress.

Laser based techniques offer non invasive means of imaging and optical signal acquisition in the biomedical field. Laser Doppler flowmetry and laser speckle imaging are important laser based methods in current research and have been explored for the analysis of blood flow. Doppler flow meters as well as laser speckle imagers use tissue backscattered light to non-invasively assess the blood flow rate. While because of large spatial variability and the temporal heterogeneity in tissue microvasculature, the measured blood flow rate is expressed in relative units in laser Doppler, laser speckle methods offers a whole field imaging resulting in absolute measurements of flow velocity. Measurement of and analysis of blood flow is vital in evaluating normal as well as differently diseased conditions of the human body. Several parameters related to flow along with flow velocity are important in characterizing tissues based on blood flow. Complexity of the flow is one of such important parameters which could be explored by looking at the fractality of the acquired Doppler signals / speckle images. In this paper, we are comparing the results of blood flow complexities assessed through fractal dimensions of Doppler signals and speckle images acquired from different parts of the body. The method adopted is expected to serve as a helping tool in characterizing normal and malignant tissues with associated variation in blood flow complexities based on the values of obtained fractal dimensions in such cases.

Blood flow through the abdominal aorta and iliac arteries is a crucial area of research in hemodynamics and cardiovascular diseases. To get in to the problem, this study presents detailed analyses of blood flow through the abdominal aorta, together with left and right iliac arteries, under Earth gravity and weightless conditions, both at the rest stage, and during physical activity. The analysis were conducted using ANSYS Fluent software. The results indicate, that there is significantly less variation in blood flow velocity under weightless conditions, compared to measurement taken under Earth Gravity conditions. Study presents, that the maximum and minimum blood flow velocities decrease and increase, respectively, under weightless conditions. Our model for the left iliac artery revealed higher blood flow velocities during the peak of the systolic phase (systole) and lower velocities during the early diastolic phase (diastole). Furthermore, we analyzed the shear stress of the vessel wall and the mean shear stress over time. Additionally, the distribution of oscillatory shear rate, commonly used in hemodynamic analyses, was examined to assess the effects of blood flow on the blood vessels. Countermeasures to mitigate the negative effects of weightlessness on astronauts health are discussed, including exercises performed on the equipment aboard the space station. These exercises aim to maintain optimal blood flow, prevent the formation of atherosclerotic plaques, and reduce the risk of cardiovascular complications.

Blood flow assessment is an emerging technique that allows for assessment of hemodynamics in the heart and blood vessels. Recent advances in cardiovascular imaging technologies have made it possible for this technique to be more accessible to clinicians and researchers. Blood flow assessment typically refers to two techniques: measurement-based flow visualization using echocardiography or four-dimensional flow magnetic resonance imaging (4D flow MRI), and computer-based flow simulation based on computational fluid dynamics modeling. Using these methods, blood flow patterns can be visualized and quantitative measurements of mechanical stress on the walls of the ventricles and blood vessels, most notably the aorta, can be made. Thus, blood flow assessment has been enhancing the understanding of cardiac and aortic diseases; however, its introduction to clinical practice has been negligible yet. In this article, we aim to discuss the clinical applications and future directions of blood flow assessment in aortic surgery. We then provide our unique perspective on the technique's translational impact on the surgical management of aortic disease. Articles from the PubMed database and Google Scholar regarding blood flow assessment in aortic surgery were reviewed. For the initial search, articles published between 2013 and 2023 were prioritized, including original articles, clinical trials, case reports, and reviews. Following the initial search, additional articles were considered based on manual searches of the references from the retrieved literature. In aortic root pathology and ascending aortic aneurysms, blood flow assessment can elucidate postoperative hemodynamic changes after surgical reconfiguration of the aortic valve complex or ascending aorta. In cases of aortic dissection, analysis of blood flow can predict future aortic dilatation. For complicated congenital aortic anomalies, surgeons may use preoperative imaging to perform "virtual surgery", in which blood flow assessment can predict postoperative hemodynamics for different surgical reconstructions and assist in procedural planning even before entering the operating room. Blood flow assessment and computational modeling can evaluate hemodynamics and flow patterns by visualizing blood flow and calculating biomechanical forces in patients with aortic disease. We anticipate that blood flow assessment will become an essential tool in the treatment planning and understanding of the progression of aortic disease.

The analysis of blood flow in blood vessels, particularly in arteries, is a topic with important clinical applications. The blood can undergo a reduction in its viscosity under shear stress, which is called shear thinning. In this study, the effect of the shear thinning of blood is simulated using the Carreau-Yasuda model, neglecting the viscoelastic effects. The purpose of this investigation is to analyze the pulsatile blood flow in a three-dimensional model of the carotid artery and the effects of occlusion using Ansys Fluent. The results obtained in this study show that, compared to Newtonian fluids, non-Newtonian fluids exhibit significant differences in secondary flow patterns and shear flow behavior. Additionally, the axial velocity in the non-planar branch decreases with obstruction. The maximum shear stress of the walls with Newtonian fluid viscosity exhibits a significant error, and the values are lower than those of walls with non-Newtonian viscosity in most cases. In continuation of this research, vessel occlusion models with different occlusion sizes are analyzed. In the case where the outlet of the vessel is narrowed, an increase in velocity is observed in the furcation area. Although the software cannot simulate rupture, occlusion of the vessel at 80\% and 50\% of the internal diameter is analyzed.

Computational analysis of blood flow in the retinal arteries and veins using fundus image

Assessment of blood flow in the left ventricle using four-dimensional flow MRI requires accurate left ventricle segmentation that is often hampered by the low contrast between blood and the myocardium. The purpose of this work is to improve left-ventricular segmentation in four-dimensional flow MRI for reliable blood flow analysis. The left ventricle segmentations are first obtained using morphological cine-MRI with better in-plane resolution and contrast, and then aligned to four-dimensional flow MRI data. This alignment is, however, not trivial due to inter-slice misalignment errors caused by patient motion and respiratory drift during breath-hold based cine-MRI acquisition. A robust image registration based framework is proposed to mitigate such errors automatically. Data from 20 subjects, including healthy volunteers and patients, was used to evaluate its geometric accuracy and impact on blood flow analysis. High spatial correspondence was observed between manually and automatically aligned segmentations, and the improvements in alignment compared to uncorrected segmentations were significant (P < 0.01). Blood flow analysis from manual and automatically corrected segmentations did not differ significantly (P > 0.05). Our results demonstrate the efficacy of the proposed approach in improving left-ventricular segmentation in four-dimensional flow MRI, and its potential for reliable blood flow analysis. Magn Reson Med 79:554-560, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

A cerebral infarction occurs when a blood vessel in the brain becomes occluded by a thrombus, blocking the flow of blood. A thrombus formed in the heart can travel through the bloodstream and obstruct cerebral vessels. Such thrombi often develop in the left atrium during atrial fibrillation, particularly within a protruding, pouch-like structure known as the left atrial appendage(LAA). Computational Fluid Dynamics (CFD) analyses of blood flow in the left atrium under both normal rhythm and atrial fibrillation have been employed in previous studies. The aim of the present study is to identify left atrial geometries that promote thrombus formation in the left atrial appendage by comparing blood flow patterns between normal and fibrillating boundary conditions.

This paper describes a high frequency ultrasound (US) imaging system for observation of small tissues and a virtual endoscopic image of a blood vessel. This system consists of a US probe with a central frequency of 32 MHz, a microscope table designed to collect some slices of US brightness mode (B-mode) images, a transmitter containing control logic and a receiver circuit and a personal computer (PC) with an analog to digital (AD) converter. First, US B-mode images with high spatial resolution were obtained by shifting a measurement plane at a constant step of 0.075 mm. Second, three-dimensional (3-D) image reconstruction was performed with linear interpolation and a volume rendering technique. Finally, the point of view of the 3-D image was set in the human body and a virtual endoscopic image was presented. The experimental results present a blood vessel as if an ultrasound probe were inserted in it and reveal the anatomical structure under skin.

Blood behaves like either a Newtonian or Non-Newtonian fluid depending on the shear stress it experiences. In the current study, a 3D model of a human bifurcated carotid artery was used to get insights into the differences between Newtonian and Non-Newtonian blood flow. As the experimental or numerical setup will be made simpler by representing blood as a Newtonian fluid. We are interested in whether it makes sense to represent blood as a Newtonian fluid. Fluent (ANSYS, 15) software was used to run two different simulations, one for blood as a Newtonian fluid and the other for a Non-Newtonian fluid. The Carreau model has been used to define the Non-Newtonian behavior of blood. A qualitative and quantitative comparison of Newtonian and Non-Newtonian blood flow has been done based on blood velocity, pressure, and wall shear stress (WSS). All comparisons were done at the minimum and maximum intake velocities of a cardiac cycle. To evaluate how close Newtonian and Non-Newtonian results are a root mean square error (RMSE) calculation has been done. At the time of minimum inlet velocity, the differences between the corresponding Newtonian and Non-Newtonian values ranged from zero to small. Additionally, the differences between corresponding Newtonian and Non-Newtonian velocities lessen at maximum inlet velocity. The impacts of blood's Non-Newtonian behavior have been found minimal. Blood may be modeled as a Newtonian fluid for simplicity in the experimental or numerical analysis of blood flow through the carotid artery, with minimal error.

Blood is a sophisticated biological fluid with components like erythrocytes that give it non-Newtonian behavior. Hemodynamic factors such as velocity magnitude, pressure, and wall shear stress descriptors are the most important factors in the development of atherosclerosis. The wall shear stress descriptors are regulated not only by flow geometry but also by blood rheological properties. In the current study, we carried out a numerical analysis of the non-Newtonian pulsatile blood flow while taking into account a patient-specific geometry and transient boundary conditions. Non-Newtonian blood flow is modeled using the four non-Newtonian models: the power-law model, the Carreau model, the Casson model, and the Quemada model, and compared with the Newtonian model. Streamline analysis vividly illustrates velocity patterns, revealing the presence of recirculation zones near sinus regions. The study suggests the significance of selecting appropriate viscosity models for accurate assessments, particularly in regions with low time-average wall shear stress values, such as those associated with atherosclerotic plaques. The differences in the time-averaged wall shear stress between the four non-Newtonian models were found to be the highest in the Quemada model. The study concluded that the non-Newtonian model is required when the focus is on the low-time-averaged wall shear stress area.

Tip Design of Hemodialysis Catheters Influences Thrombotic Events and Replacement Rate

Performance modeling and analysis of blood flow in elastic arteries

A proper analysis of blood flow is contingent upon accurate modelling of the branching pattern and vascular geometry of the network of interest. It is challenging to reconstruct the entire vascular network of any organ experimentally, in particular the pulmonary vasculature, because of its very high number of vessels, complexity of the branching pattern and poor accessibility in vivo. The objective of our research is to develop an innovative approach for the reconstruction of the full pulmonary vascular tree from available morphometric data. Our method consists of the use of morphometric data on those parts of the pulmonary vascular tree that are too small to reconstruct by medical imaging methods. This method is a three-step technique that reconstructs the entire pulmonary arterial tree down to the capillary bed. Vessels greater than 2 mm are reconstructed from direct volume and surface analysis using contrast-enhanced computed tomography. Vessels smaller than 2 mm are reconstructed from available morphometric and distensibility data and rearranged by applying Murray's laws. Implementation of morphometric data to reconstruct the branching pattern and applying Murray's laws to every vessel bifurcation simultaneously leads to an accurate vascular tree reconstruction. The reconstruction algorithm generates full arterial tree topography down to the first capillary bifurcation. Geometry of each order of the vascular tree is generated separately to minimize the construction and simulation time. The node-to-node connectivity along with the diameter and length of every vessel segment is established and order numbers, according to the diameter-defined Strahler system, are assigned. In conclusion, the present model provides a morphological foundation for future analysis of blood flow in the pulmonary circulation