%0 Journal Article %A Nathan H. Williamson %A Michal E. Komlosh %A Dan Benjamini %A Peter J. Basser %T Limits to flow detection in phase contrast MRI %D 2020 %R 10.1101/2020.03.20.000638 %J bioRxiv %P 2020.03.20.000638 %X Pulsed gradient spin echo (PGSE) complex signal behavior becomes dominated by attenuation rather than oscillation when displacements due to flow are similar or less than diffusive displacements. In this “slow-flow” regime, the optimal displacement encoding parameter q for phase contrast velocimetry depends on the diffusive length scale rather than the velocity encoding parameter venc = π/(qΔ). The minimum detectable mean velocity using the difference between the phase at +qslow and −qslow is . These theories are then validated and applied to MRI by performing PGSE echo planar imaging experiments on water flowing through a column with a bulk region and a beadpack region at controlled flow rates. Velocities as slow as 6 µm/s are detected with velocimetry. Theories, MRI experimental protocols, and validation on a controlled phantom help to bridge the gap between porous media NMR and pre-clinical phase contrast and diffusion MRI.Competing Interest StatementThe authors have declared no competing interest. %U https://www.biorxiv.org/content/biorxiv/early/2020/07/15/2020.03.20.000638.full.pdf