Fig. 2

Examples of 4D Flow CMR visualization techniques. All examples are based on data acquired in the aorta of a healthy volunteer. In these examples, flow visualization is overlaid onto a segmentation of the aorta. a An oblique slice that transects the aorta has been color-coded by flow speed and combined with a graph of velocity vectors which here displays the speed and direction of blood velocity in black arrows at a coarser grid than the acquired voxels. This type of visualization provides a quick overview of velocity fields. b A maximum intensity projection (MIP) image of flow speed permits identification of areas of elevated velocity and the point of peak velocity while displaying the peak velocities of the whole volume projected onto this single slice image. c Streamlines are instantaneously tangent to the velocity vector field and are useful to visualize 3D velocity fields at discrete time points. Here, the peak systolic velocity field is shown. d Pathlines are the trajectories that massless fluid particles would follow through the dynamic velocity field. Pathlines are suitable for studies of the path of pulsatile blood flow over time. This example shows pathlines emitted from a plane in the ascending aorta at the onset of systole and traced to early systole (left), peak systole (middle) and late systole (right). All figures have been color-coded based on flow speed using the same color-window settings according to the scale shown in (b) and (d). In a, c and d, the visualizations have been combined with a PC-MRA isosurface which has been derived from the 4D Flow CMR data