A method of determining rheological properties of a fluid. The method includes: providing an open-bore tube and defining within the bore a three dimensional grid (3DG) of voxels; defining at least an inlet cross section (ICS) and an outlet cross section (OCS); defining a volume of interest within the bore between the ICS and the OCS; obtaining rheological properties of the fluid; applying a pressure gradient to the bore between the ICS and the OCS; and nuclear magnetic resonance imaging the fluid within the volume of interest to determine various aspects of the fluid.