High resolution renal diffusion imaging using a modified steady-state free precession sequence.

A modified steady-state free precession (SSFP) diffusion sequence is proposed for high resolution renal imaging. A pair of bipolar diffusion gradients was used to minimize the errors in measured apparent diffusion coefficient (ADC) caused by variations in T1, T2, and RF flip angle that have been observed with previously employed SSFP diffusion sequences. Motion sensitivity was reduced by the use of compensated gradients, frame-by-frame averaging, and a repetition time of 22 ms, which for a single-acquisition 128 x 128 image requires only 3 s. High resolution was achieved by signal averaging. The modified sequence was applied to in vivo diffusion measurements. In six normal rat kidneys the ADCs (mean +/- SD; x 10(-3) mm2/s) of the cortex, outer medulla, and inner medulla were 2.28 +/- 0.05, 2.38 +/- 0.10, and 2.95 +/- 0.05, respectively. The technique requires relatively large gradients to achieve adequate diffusion weighting.