Abstract
It is reported that the wall shear stress affects the biochemical function of endothelial cells such as the production of nitric oxide (NO), which has an anti-arteriosclerosis effect, and the generation and development of arteriosclerosis plaque. On the other hand, the shear stress in a stream distant from the wall also provides important information, and it is reported that the stream shear stress affects the deformation of erythrocytes. Therefore, if these intravascular shear stresses can be assessed quantitatively and noninvasively, it is expected that useful information can be supplied for the prevention of arteriosclerosis. The conventional method for shear stress estimation, which combines vascular reconstruction using MRI or IVUS, and CFD requires improvements in order to provide real-time processing and more a quantitative estimation. In this paper, a novel method that enables a real-time, quantitative estimation of intravascular shear stress distribution is proposed. It is based on using Newton's law of viscosity and the estimated viscosity coefficient and shear rate obtained by ultrasonic velocity measurement. An experimental investigation was performed in which two types of fluids with different viscosity coefficients (water, and water mixed by PVA) were flowed at a constant flow rate (20 mL/s) in a silicone tube with a plaque-like step. After ultrasonically measuring the velocity vector distribution in the tube, the viscosity coefficient, shear rate and shear stress were estimated based on the proposed method. Using the proposed method, the averaged error in the estimated value of the viscosity coefficient compared to the value measured using a viscometer was 9%. The averaged value of the shear stress distribution estimated in the higher viscosity fluid (water mixed by PVA: 1.0 Pa) became larger than that in the lower viscosity fluid (water: 0.2 Pa). These results reveal that the proposed method is technically valid for quantitative shear stress estimation.
