Abstract
The shear stress on endothelial cells influences blood vessel disease. This stress depends on blood flow velocity and its distribution near the internal wall of a blood vessel. Blood flow velocity can be measured by the phase contrast method in magnetic resonance imaging, where the phase of the signal reflects the velocity. There are several parameters that influence the accuracy of velocity measurement: dephasing, relaxation time, and sequence parameters. Although the effects of these parameters have been elucidated using measured results at a particular point, the shape of the velocity profile needs to be evaluated in order to identify the shear stress on an endothelial cell. From the results of this study, we propose the parameters that define the velocity profile in the laminar flow regime and evaluate their effects. The results are then applied to evaluate the velocity profile in a U-shaped tube. We then propose the mean and standard deviation at various distances from the center of the tube as the parameters for expressing the velocity profile, because the mean value gives a parabolic distribution and the standard deviation is proportional to the distance from the center in the laminar flow regime. The relaxation time, repetition time, velocity encoding number and oversampling or phase-encoding direction can influence the velocity profile. The velocity encoding number is the velocity when the phase is 180 degrees. Similar effects were observed for the flow in a U-shaped tube. Based on the results for the laminar flow regime, the velocity profile in a U-shaped tube could therefore be evaluated more accurately using the phase contrast method.
