The PGEM allows loading and analyzing data generated by 4D Flow MRI acquisitions. The workflow is very similar to the one described for DTI Tractography, and the applied tracking methods are exactly the same.
In 4D Flow analysis, the flow velocity vector takes the role of the principal tensor eigenvector in the DTI analysis. The result of the analysis are "streamlines", comparable to the fiber tracks of DTI tractography. Streamlines connect the velocity vectors at a given acquisition time, and give a general impression of the flow pattern at that time. As 4D Flow measurements acquire the velocity vectors at multiple times, e.g. at different phases of a heartbeat, streamlines can be calculated at every acquisition time. As a result, the change of the flow pattern over time can conveniently be visualized as a movie.
An alternative analysis is the flow tracking along time, connecting the velocity vectors of successive acquisition and thereby mimicking the trajectory a particle might trace during the acquisition. The result of such an analysis are called "pathlines". As of now, PGEM doesn't support the generation of pathlines, only streamlines.