About the Origins of Diffusion-Weighting Due to the Non-Linear Phase Dispersion Induced by Frequency-Swept Pulses

Julien Valette^1,2, Denis Le Bihan², Franck Lethimonnier²

It has been recognized in the past that the non-linear phase induced by frequency-swept pulses may cause diffusion-weighting. In the present work, the origins of the non-linear phase dispersion induced by frequency-swept pulses are revisited, in order to assess whether the phase variation of the B1 field during the sweep should be explicitly considered when calculating diffusion weighting. Following this analysis, an analytical expression is derived for diffusion-weighting induced by a pair of slice selective hyperbolic secant pulses, and confronted to numerical simulation of the Bloch equations including diffusion.