Optimisation of Velocity Encoding Gradients for Phase Contrast Gas Velocity Taking Diffusion Into Account.

Lionel Martin¹, Xavier Matre¹, Mathieu Sarracanie¹, Marlies Friese², Ludovic de Rochefort¹, Rose-Marie Dubuisson¹, Emeline Boriasse¹, Emmanuel Durand¹

MR flow measurement techniques have mostly been used in liquids. For coherent motion (flow), bipolar gradients induce a phase shift and a signal drop for incoherent motion (diffusion). This effect, negligible for liquids, cannot be neglected for gases. Competition between these two phenomena results in the existence of an optimal FOS that could be theoretically determined. 2D velocity maps of parabolic flows were acquired with different FOS and gases. Results show that velocity error is a function of the FOS and a different optimal FOS is reached for each gas. Thus, they validate our theoretical simulations.