High-resolution diffusion-weighted 3D MRI, using diffusion-weighted driven-equilibrium (DW-DE) and multishot segmented 3D-SSFP without navigator echoes

In this work we report on the development of a novel technique for high‐resolution diffusion‐weighted (DW) MRI based upon 3D steady‐state free precession (3D‐SSFP). First the 3D‐SSFP acquisition was segmented (each segment consisting of a series of RF pulses and gradient‐recalled echoes), and then DW‐driven equilibrium (DE) was inserted between each segment. The in‐plane imaging matrix was typically 256 × 192 or 256 × 160, which resulted in high‐resolution DW images. The DW‐DE segmented SSFP signal was contaminated by the non‐DW magnetization, which recovered and contributed signal during the readout train (T1 contamination). Center‐out slice encoding was used to place the greatest diffusion weighting at the center of k‐space. A numerical simulation and supporting experiments were performed to evaluate the relationship of the transverse magnetization to imaging parameters, such as the b‐value, echo‐train length (ETL), echo‐train (group) repetition time (TRg), and RF excitation TR (Δt). Both the numerical simulation and the experiments suggested that the effect of T1 contamination would be reduced with a longer TRg, smaller b‐value, shorter ETL, and center‐out slice phase encoding. Phase errors caused by microscopic motions during the diffusion gradients were converted into amplitude errors by the tip‐up pulse at the end of the diffusion‐weighting segment. As a result, small bulk motions, such as CSF pulsation, did not cause motion‐related ghosting artifacts, which would be typical in images from other multishot DWI techniques. This technique can be used for high‐resolution DWI of nonbrain anatomies. Magn Reson Med 50: 821–829, 2003. © 2003 Wiley‐Liss, Inc.