High speed diffusion imaging in the presence of eddy currents.

This paper describes two schemes for fast diffusion imaging on a 1.5T MRI unit with unshielded gradients and 10-mT/m gradient system. The prepared longitudinal magnetization is sampled by a turbo fast low-angle shot (FLASH) sequence. The first scheme involves modifications to a diffusion-weighted driven-equilibrium preparation sequence that yields quantitative diffusion imaging. The second scheme consists of four 90 degree pulses that form the preparatory period with diffusion gradients applied between the first and last two 90 degrees pulses. Sufficient time is allowed between the diffusion gradients and the beginning of the echo readout to allow eddy currents to decay to an acceptable level. Phantom studies show agreement between diffusion coefficients in the literature with those determined using the above schemes. The potential application of these sequences in monitoring temperature is demonstrated in phantoms. Artifact-free quantitative diffusion-weighted images of the brain using the second scheme are presented.