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.