Advances and artefact suppression in RARE-velocimetry for flow with curved streamlines

Method and considerations are presented that allow for an improved quantitative velocity measurement of complex fluids under shear using a fast 2D PGSE-RARE technique. While this contribution is relevant for shear geometries with rotational symmetry in general, the focus here is set on cylindrical Couette cells, a device most commonly used for rheological NMR investigations. The curved nature of the flow within the shearing geometry creates challenges in accurately determining the flow profile, as conventional imaging gradients naturally operate on a Cartesian grid. In particular the appropriate slice thickness in the flow direction and the applied k-space trajectory are discussed. For the latter an MRI simulation program has been written that numerically solves the Bloch equations and allows for the investigation of out-of-pixel flow. Furthermore, we present ways of increasing the spatial resolution across the gap of cylindrical Couette cells while still providing 2D imaging capabilities under certain conditions, thus allowing for a more detailed quantification of flow profiles as necessary for the analysis of complex fluid flow.