Exploring hemodynamics by raycasting 4D MRI flow

Flow sensitive phase-contrast magnetic resonanceimaging sequences produce three-dimensional velocityfields in time, providing quantitative information ofblood flow dynamics. Thorough understanding of thehemodynamic behavior will support physicians to diagnose and assess risk of various cardiovascular diseases. However, inspection of the complex cine flowdata, encompassing both morphology and function,is generally a troublesome and tedious task. Overthe last few decades, the field of scientific flow visualization has introduced a multitude of techniques to explore unsteady velocity fields, in order to capture and depict flow characteristics. Inspired by concepts from ultrasound imaging, we have investigated raycasting as a means to explore and visualize direction and magnitude of blood velocities, striving to reveal the blood flow behavior. In particular, we aim to depict flow patterns that deviate from the expected blood flow. For that purpose, several interaction techniques have been incorporated into the presented framework. Angles between a user-defined direction, set by an interaction widget, and the velocity field are mapped to different visual cues using a transfer function. Furthermore, we define the prevalent flow as approximate of the expected blood flow, generated based on the vessel centerline. We visualize a projection of the angles between the prevalent flow and the velocity field.