Shuya Shida

Properties of N-Butyl Cyanoacrylate–iodized Oil Mixtures for Arterial Embolization: In Vitro and In Vivo Experiments

PURPOSE To examine the properties of N-butyl cyanoacrylate (NBCA) and iodized oil (lipiodol [Lip]) in vitro and in vivo for safe and effective embolization. MATERIALS AND METHODS Viscosity, polymerization time, and diffusing capacity were evaluated according to the NBCA/Lip ratio in vitro. Additionally, the effect of the NBCA/Lip ratio on arterial embolization was evaluated in vivo; various ratios of NBCA/Lip were injected into the renal arteries of adult beagles, after which the embolization effect following transcatheter arterial embolization was quantitatively investigated histopathologically and using computed tomography (CT) volumetry. RESULTS The viscosity of NBCA/Lip increased, polymerization time was prolonged, and diffusing capacity increased as the NBCA density decreased. As the NBCA density decreased, embolic material was recognized in smaller diameter arteries, and embolization of a larger vascular bed was accomplished. The NBCA/Lip mixture with a low density of NBCA was located more peripherally from the catheter tip, and embolization of more peripheral and smaller diameter arteries was achieved. CONCLUSIONS The relationships of properties of NBCA/Lip in vitro and embolization effects in vivo of various ratios of NBCA/Lip were quantitatively examined and compared. The results of this study are useful for safe and effective embolization.

Influence of Plaque Stiffness on Change of Blood Vessel Geometry Leading Hemodynamical Changes in PVA-H Stenosis Models

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.Copyright

Development of a Methodology for Adaptation of Refractive Index Under Controlling Kinematic Viscosity for PIV

Blood vessel diseases such as ischemic cardiac disease or cerebral aneurysm are life-threatening disorders and as large a cause of death as cancer in many countries. The rupture of a cerebral aneurysm usually causes subarachnoidal hemorrhage the mortality of which is very high. Previous studies have proved that the genesis and growth of aneurysm are related to hemodynamics. Especially, in endovascular therapy for cerebral aneurysms using medical devices such as coils or stents, hemodynamics in an aneurysm are related to thrombosis formation in the aneurysm and to its repair. In vascular research using a biomodel (blood vessel phantom with mechanical properties similar to a human artery) for treating cerebral aneurysm, the working fluid, termed Blood-Mimicking Fluid (BMF), should mimic human blood with respect to viscosity so as to obtain realistic blood flow modeling in in vitro measurements. Moreover, refractive indices of BMF must be adjusted to fit biomodel materials because the materials used for Particle Image Velocimetry, one of the best tools for measurement of flow, have various refractive indices. For simultaneous adjustment of the two parameters, i.e. kinematic viscosity and refractive index, an aqueous mixture of glycerol and sodium iodide has been used in previous research. In this paper, we develop a systematic way to precisely find the two targeted parameters of BMF by showing the measurement values of the refractive index and the viscosity of the two aqueous solutions. The refractive index to light of fluorescent was measured with a critical angle refractometer while temperature of sample was also measured. And a vibration-type viscometer was used to obtain the dynamic viscosity under the same condition as refractive index measurement. These measurements were carried out at room temperature and pressure, respectively. As a result of detailed measurements at various proportions, refractive indices of the aqueous solution of glycerol (Gly. aq.) increase monotonically. On the one hand, the kinematic viscosity of Gly. aq. increases very slightly with its proportion and that of the aqueous solution of sodium iodide (NaI aq.) exhibits unique behavior. The results of combining Gly. aq. and NaI aq. indicate that the mixture has a wide range of kinematic viscosity, including the value of blood (around 3.8 mm2 /s), at the targeted refractive index. In conclusion, this mixing method is useful for BMF preparation with the adjustment of refractive index and kinematic viscosity.Copyright

Mechanical Properties of Tube-Shaped Poly (Vinyl Alcohol) Hydrogel Blood Vessel Biomodel

Biomodels, which mimic the shape and motion of blood vessels, have been developed for clinical training in endovascular intervention and for the technical development of interventional devices such as stents. The present authors have developed a biomodel made of poly (vinyl alcohol) hydrogel (PVA-H), which has good transparency, low surface friction, and dynamic viscoelasticity similar to that of arteries. However, evaluation of its behavior as an arterial biomodel has not been carried out. In order to develop a PVA-H biomodel which can accurately mimic the motion of blood vessels, it is necessary to measure and match its mechanical properties in a tube shape mimicking blood vessels. In this study, tube-shaped PVA-H biomodels were prepared, and their mechanical properties were evaluated as to pulse wave velocity (PWV), compliance, and transfer function. PWV was calculated with Young’s modulus and dimensions of the biomodels. A tube-shaped PVA-H model and a model made of commercial silicone were set in a pulsatile flow path apparatus filled pure water (23°C). Sinusoidal pulsatile waves of various frequencies generated by a screw pump were released into flow path. The flow rate, the inner pressure, and the diameter of the biomodels were measured. The compliance of a biomodel was calculated with changing pressures and diameters. The transfer function was obtained as the ratio of the amplitude of the pressure in front of a biomodel and that behind it. The two kinds of biomodels studied showed PWV similar to that of real arteries: PVA-H shows lower PWV which younger arteries tend to show, while silicone shows higher PWV, similar to the case of aged arteries. In compliance, PVA-H shows a value similar to that of arteries in the lower pressure range, whereas silicone shows a value similar to that of arteries at higher pressure. A difference of transfer function in relation to the pulsatile frequencies was observed. This phenomenon is similar to that of real blood vessels and explainable in terms of the theory of the forced vibration in single-degree-of-freedom systems with attenuation. The transfer function is affected by mechanical properties of the wall, and the difference between biomodels is due to the viscoelasticity of the biomodels. With PVA-H, these parameters can be gradually changed by adjusting factors such as concentration. These findings indicate that PVA-H would be useful for the development of biomodels.Copyright

PIV Measured Hemodynamic Study With Several Stents in a Cerebral Aneurysm Model for New Stent Design

The rupture of an aneurysm can lead to a subarachnoid hemorrhage, which can be a fatal illness in a large percentage of cases. In treating aneurysm intravascular stenting is thought as a better option compared with clipping treatment. The treatment of cerebral aneurysm with a porous stent also has recently proposed as a minimally invasive way to prevent rupture and favor coagulation mechanism inside aneurysm. The analysis of a flow pattern with and without stent in cerebral aneurysm model was performed with Particle Image Velocimetry (PIV). Three types of stents were used in the present investigation and the porosity of stent 1, 2 and 3 is 80%, 74% and 64%, respectively. Reduced velocity, smaller average vorticity magnitude and different flow patterns inside aneurysm are observed when the three different proposed stents are used. The stent 3 (Porosity = 64%) decrease the magnitude of the velocity by 98% and change the flow pattern in the aneurysm. Our results show that not only the role of the porosity but also the stent shape affect the flow and help us understand the characteristic of stent designs.Copyright