MR Velocimetry Protocols for Small Water-Filled Channels

Unlike optical velocimetry methods, nuclear magnetic resonance (NMR) relaxes the requirement of having optical access to flow, and additionally allows multiple field-specific contrast mechanisms (fluid displacement, diffusion, chemical species, etc). For small channel networks, the trade-offs between spatial and temporal resolutions leads to the following conundrum: it is better to obtain spatially resolved velocity fields but only for slowly evolving flows, or temporally resolved average velocities in each of the small channels? To explore this issue, we compare a fast and localized NMR velocimetry technique based on multiple modulation multiple echoes (MMMEV), with classical NMR imaging velocimetry protocols (flow-compensated phase-contrast spin-echo, pulse-gradient spin-echo, and spin-tagging spin-echo) in a microchannel network.