Flow Visualization and Vectors YangZifeng JohnsonMark 2019 A dye visualization experiment was designed and operated as an analogy of the X-ray angiographic imaging. Visualization of the soluble dye injected into the water flow, taking advantage of the transmittance of visible light, served as the analogy of the X-ray angiographic imaging process. Optical flow method was used to recover the velocity field from the dye visualization images. The results from the dye visualization measurements were compared with the PIV flow measurements in the middle plane of the tube at different time instants for a pulsatile flow. The purpose of this study was to quantify the accuracy of velocity field estimation from the transmittance-based two-dimensional projection image of the three-dimensional volumetric flow field in comparison with the PIV measurements.