Marie Oshima

Simultaneous measurement of internal and surrounding flows of a moving droplet using multicolour confocal micro-particle image velocimetry (micro-PIV)

This paper presents a micro-multiphase flow measurement technique, multicolour confocal micro-particle image velocimetry (PIV), and its application to the internal and surrounding flow measurement of a droplet moving through a microchannel. The present system measures the dynamic interaction between flows in two different phases, such as solid–liquid or liquid–liquid, simultaneously and separately. Unlike conventional confocal micro-PIV, this system features a wavelength separation optical device. The optical components (e.g., filters and dichroic mirror) are designed to separate fluorescent lights of tracer particles and to eliminate unnecessary scattered light depending on the characteristic wavelengths. The system can record a sequence of images at up to 2000 frames per second. It also has an in-plane spatial resolution of 0.284 µm/pixel in a field of 227.2 µm × 170.4 µm and a confocal depth of 3.43 µm using ∅1.0 µm particles and a 40× objective lens. This paper examines the performance of the present system, such as its ability to separate wavelengths. Furthermore, this system is applied to liquid–liquid two-phase flow, which consists of a water droplet and surrounding oil flow, in a microchannel. We succeeded in measuring each phase movement separately and simultaneously. As a result of the estimation of the out-of-plane velocity component, a three-dimensional flow structure is obtained and the interaction between each phase is investigated.

Patient-Specific Modeling and Multi-Scale Blood Simulation for Computational Hemodynamic Study on the Human Cerebrovascular System

To develop a targeted drug delivery system for cerebrovascular disorders such as stroke, it is important to obtain detailed information on flow rates and hemodynamics of the human cerebrovascular system for individual patients. A patient-specific integrated numerical simulation system has been developed by the authors such that vascular geometry is constructed from medical images such as magnetic resonance imaging (MRI) or computed tomography (CT) data, and computational conditions are modeled mathematically to represent the realistic in vivo environments. In general, the three-dimensional numerical simulation using a patient-specific model is conducted only for a localized diseased region with atherosclerosis or an aneurysm. Although the analysis region is only a part of the circulatory system, the simulation should include the effects from the entire circulatory system. Since the peripheral network determines the flow distributions in the cerebrovascular system, the paper reviews the recent simulation methods to take into account the network by coupling the image-based three-dimensional simulation with a one- and zero-dimensional simulations as an outflow boundary condition The paper shows the mathematical modeling of the multi-scale outflow boundary condition and its applications to patient- specific models of the arterial circle of Willis. The results are compared to those using the conventional, free-stream boundary condition. As a result, the multi-scale outflow boundary condition shows a significant difference in flow rate of each artery and in flow distribution in the arterial circle of Willis.

Numerical Study of Cerebroarterial Hemodynamic Changes Following Carotid Artery Operation: A Comparison Between Multiscale Modeling and Stand-Alone Three-Dimensional Modeling

Free outflow boundary conditions have been widely adopted in hemodynamic model studies, they, however, intrinsically lack the ability to account for the regulatory mechanisms of systemic hemodynamics and hence carry a risk of producing incorrect results when applied to vascular segments with multiple outlets. In the present study, we developed a multiscale model capable of incorporating global cardiovascular properties into the simulation of blood flows in local vascular segments. The multiscale model was constructed by coupling a three-dimensional (3D) model of local arterial segments with a zero-one-dimensional (0-1-D) model of the cardiovascular system. Numerical validation based on an idealized model demonstrated the ability of the multiscale model to preserve reasonable pressure/flow wave transmission among different models. The multiscale model was further calibrated with clinical data to simulate cerebroarterial hemodynamics in a patient undergoing carotid artery operation. The results showed pronounced hemodynamic changes in the cerebral circulation following the operation. Additional numerical experiments revealed that a stand-alone 3D model with free outflow conditions failed to reproduce the results obtained by the multiscale model. These results demonstrated the potential advantage of multiscale modeling over single-scale modeling in patient-specific hemodynamic studies. Due to the fact that the present study was limited to a single patient, studies on more patients would be required to further confirm the findings.

An integrated geometric modelling framework for patient-specific computational haemodynamic study on wide-ranged vascular network

Patient-specific haemodynamic computations have been used as an effective tool in researches on cardiovascular disease associated with haemodynamics such as atherosclerosis and aneurysm. Recent development of computer resource has enabled 3D haemodynamic computations in wide-spread arterial network but there are still difficulties in modelling vascular geometry because of noise and limited resolution in medical images. In this paper, an integrated framework to model an arterial network tree for patient-specific computational haemodynamic study is developed. With this framework, 3D vascular geometry reconstruction of an arterial network and quantification of its geometric feature are aimed. The combination of 3D haemodynamic computation and vascular morphology quantification helps better understand the relationship between vascular morphology and haemodynamic force behind ‘geometric risk factor’ for cardiovascular diseases. The proposed method is applied to an intracranial arterial network to demonstrate its accuracy and effectiveness. The results are compared with the marching-cubes (MC) method. The comparison shows that the present modelling method can reconstruct a wide-ranged vascular network anatomically more accurate than the MC method, particularly in peripheral circulation where the image resolution is low in comparison to the vessel diameter, because of the recognition of an arterial network connectivity based on its centreline.

Quantitative measurement of blood flow volume in the major intracranial arteries by using 123i-iodoamphetamine SPECT.

Purpose The aim of this study was to establish the novel automatic method to quantify blood flow volumes of the major intracranial arteries by using SPECT. Methods We created the vascular templates to cover the territory supplied by the major intracranial arteries. Each blood flow volume was calculated as the regional cerebral blood flow on SPECT using this template × volume size of the template. In this study, we evaluated the volume flows in 22 cerebral hemispheres with normal perfusion and 28 hemispheres with severe stenosis in the internal cerebral artery (ICA) or middle cerebral artery (MCA) and that at acetazolamide test in 16 normal hemispheres and 20 hemispheres with stenosis. Results The mean blood flow volumes of the ICA and MCA in the normal hemispheres increased to more than 40% after acetazolamide test (161–228 mL/min for ICA and 111–157 mL/min for MCA), although those in the hemispheres with stenosis increased to less than 35% (158–192 mL/min for ICA and 107–127 mL/min for MCA). The receiver operating characteristic analyses revealed that the simple difference between the blood flow volume at acetazolamide test and that at rest using the new MCA template was superior to detecting reduction of cerebrovascular reactivity (CVR), compared with the conventional percent CVR using the original template. Conclusions Blood flow volumes of the intracranial arteries had been able to be quantified automatically on SPECT, and difference of CVR was available for predicting the blood demand-supply balance.

Arterial Location-Specific Calcification at the Carotid Artery and Aortic Arch for Chronic Kidney Disease, Diabetes Mellitus, Hypertension, and Dyslipidemia

Several risk factors for arterial calcification have been reported but controversial. The aim of this study was to clarify the interactions among chronic kidney disease (CKD), diabetes mellitus (DM), hypertension, and dyslipidemia in altering the risk of arterial calcification in the three different arterial locations and the intramural location at the internal carotid artery (ICA) origins. Calcified burdens at the ICA origins, the aortic arch, and its orifices were evaluated in a retrospective fashion by using computed tomography angiography in 397 patients. The multivariate analyses were adjusted for age, gender, CKD, DM, hypertension, dyslipidemia, and current smoking status. Additionally, subgroup analyses in each variable were conducted. Our multivariate logistic regression analyses revealed that CKD was significantly associated with the outside-wall calcification at the ICA origins, whereas DM was only associated with the inside-ICA-wall calcification. Additionally, we found that DM increased the association between CKD and arterial calcification at the aortic arch and its orifices, and the outside-wall at the ICA origins. Hypertension was significantly associated with the calcification at the orifices of the aortic arch branches synergistically with CKD. Dyslipidemia did not have any significant association with calcification in any of the three vascular beds. CKD had the highest prevalence risk of calcification in common with the three different vascular beds. CKD in combination with DM, as well as hypertension in combination with CKD, were key relationships affecting the risk of arterial calcification, especially at the aortic arch and its orifices.

Intramural location and size of arterial calcification are associated with stenosis at carotid bifurcation

PURPOSEnThe purpose of this study was to investigate the association between internal carotid artery (ICA) stenosis and intramural location and size of calcification at the ICA origins and the origins of the cervical arteries proximal to the ICA.nnnMETHODnA total of 1139 ICAs were evaluated stenosis and calcification on the multi-detector row CT angiography. The intramural location was categorized into none, outside and inside location. The calcification size was evaluated on the 4-point grading scale. The multivariate analyses were adjusted for age, serum creatinine level, hypertension, hyperlipidemia, diabetes mellitus, smoking and alcohol habits.nnnRESULTSnOutside calcification at the ICA origins showed the highest multivariate odds ratio (OR) for the presence of ICA stenosis (30.0) and severe calcification (a semicircle or more of calcification at the arterial cross-sectional surfaces) did the second (14.3). In the subgroups of >70% ICA stenosis, the multivariate OR of outside location increased to 44.8 and that of severe calcification also increased to 32.7. Four of 5 calcified carotid plaque specimens extracted by carotid endarterectomy were histologically confirmed to be calcified burdens located outside the internal elastic lamia which were defined as arterial medial calcification.nnnCONCLUSIONSnICA stenosis was strongly associated with severe calcification located mainly outside the carotid plaque. Outside calcification at the ICA origins should be evaluated separately from inside calcification, as a marker for the ICA stenosis. Additionally, we found that calcification at the origins of the cervical arteries proximal to the ICA was significantly associated with the ICA stenosis.

Calcification at orifices of aortic arch branches is a reliable and significant marker of stenosis at carotid bifurcation and intracranial arteries

PURPOSEnSimple rating scale for calcification in the cervical arteries and the aortic arch on multi-detector computed tomography angiography (MDCTA) was evaluated its reliability and validity. Additionally, we investigated where is the most representative location for evaluating the calcification risk of carotid bifurcation stenosis and atherosclerotic infarction in the overall cervical arteries covering from the aortic arch to the carotid bifurcation.nnnMETHODnThe aortic arch and cervical arteries among 518 patients (292 men, 226 women) were evaluated the extent of calcification using a 4-point grading scale for MDCTA. Reliability, validity and the concomitant risk with vascular stenosis and atherosclerotic infarction were assessed.nnnRESULTSnCalcification was most frequently observed in the aortic arch itself, the orifices from the aortic arch, and the carotid bifurcation. Compared with the bilateral carotid bifurcations, the aortic arch itself had a stronger inter-observer agreement for the calcification score (Fleiss kappa coefficients; 0.77), but weaker associations with stenosis and atherosclerotic infarction. Calcification at the orifices of the aortic arch branches had a stronger inter-observer agreement (0.74) and enough associations with carotid bifurcation stenosis and intracranial stenosis. In addition, the extensive calcification at the orifices from the aortic arch was significantly associated with atherosclerotic infarction, similar to the calcification at the bilateral carotid bifurcations.nnnCONCLUSIONSnThe orifices of the aortic arch branches were the novel representative location of the aortic arch and overall cervical arteries for evaluating the calcification extent. Thus, calcification at the aortic arch should be evaluated with focus on the orifices of 3 main branches.

Investigation of blood flow in the external carotid artery and its branches with a new 0D peripheral model

AbstractBackgroundPatient-specific modelling in clinicaln studies requires a realistic simulation to be performed within a reasonable computational time. The aim of this study was to develop simple but realistic outflow boundary conditions for patient-specific blood flow simulation which can be used to clarify the distribution of the anticancer agent in intra-arterial chemotherapy for oral cancer.MethodsIn this study, the boundary conditions are expressed as a zero dimension (0D) resistance model of the peripheral vessel network based on the fractal characteristics of branching arteries combined with knowledge of the circulatory system and the energy minimization principle. This resistance model was applied to four patient-specific blood flow simulations at the region where the common carotid artery bifurcates into the internal and external carotid arteries.ResultsResults of these simulations with the proposed boundary conditions were compared with the results of ultrasound measurements for the same patients. The pressure was found to be within the physiological range. The difference in velocity in the superficial temporal artery results in an error of 5.21xa0±xa00.78xa0% between the numerical results and the measurement data.ConclusionsThe proposed outflow boundary conditions, therefore, constitute a simple resistance-based model and can be used for performing accurate simulations with commercial fluid dynamics software.

Development of a Numerical Method for Patient-Specific Cerebral Circulation Using 1D-0D Simulation of the Entire Cardiovascular System with SPECT Data.

The detailed flow information in the circle of Willis (CoW) can facilitate a better understanding of disease progression, and provide useful references for disease treatment. We have been developing a one-dimensional–zero-dimensional (1D–0D) simulation method for the entire cardiovascular system to obtain hemodynamics information in the CoW. This paper presents a new method for applying 1D–0D simulation to an individual patient using patient-specific data. The key issue is how to adjust the deviation of physiological parameters, such as peripheral resistance, from literature data when patient-specific geometry is used. In order to overcome this problem, we utilized flow information from single photon emission computed tomography (SPECT) data. A numerical method was developed to optimize physiological parameters by adjusting peripheral cerebral resistance to minimize the difference between the resulting flow rate and the SPECT data in the efferent arteries of the CoW. The method was applied to three cases using different sets of patient-specific data in order to investigate the hemodynamics of the CoW. The resulting flow rates in the afferent arteries were compared to those of the phase-contrastxa0magnetic resonance angiography (PC-MRA) data. Utilization of the SPECT data combined with the PC-MRA data showed a good agreement in flow rates in the afferent arteries of the CoW with those of PC-MRA data for all three cases. The results also demonstrated that application of SPECT data alone could provide the information on the ratios of flow distributions among arteries in the CoW.