SUMMARY: 3D diffusion-weighted steady-state free precession imaging (3D DW-SSFP) with isotropic resolution was performed to delineate structures of the human lumbosacral plexus (LSP). 3D DW-SSFP clearly revealed detailed anatomy of the LSP and its branches. Our data suggest that the sequence based on 3D DW-SSFP can be used for high-resolution MR imaging of the peripheral nervous system. MR imaging evaluation of the normal peripheral nerve anatomy and diseases is mainly dependent on 2D MR imaging techniques, including T1-weighted spin-echo, T2-weighted fast spin-echo, and inversion-recovery sequences with fat saturation.1-7 Although these techniques can produce excellent-quality images, they have limitations in describing deliberate orientations of the targeted nerves, in that section gaps in these techniques lead to lower anatomic coverage and less quantitative information. Furthermore, T2-weighted spin-echo techniques cannot image smaller nerves in the periphery because the nerves cannot be distinguished from blood vessels on T2-weighted spin-echo images.8 A combination of diffusion-weighted imaging (DWI) with fat-suppressed T2-weighted sequences has been proposed to overcome these technical limitations. Additionally, DWI based on spin-echo with an echo-planar readout has been used to evaluate the anatomy of the peripheral nervous system. 9-10 However, these conventional techniques have limited spatial resolution or low signal-to-noise ratio and often produce severe image distortion. 8,11 It is difficult to reveal the detailed anatomy of the lumbosacral plexus (LSP) by using conventional MR imaging in that many important branches of the LSP are small, and contrast of the various anatomic structures is not sufficient to exhibit their discrete identification. The purpose of this study is to describe a high-spatial-resolution 3D diffusion-weighted steady-state free precession (3D DW-SSFP) sequence and prospectively evaluate its feasibility in human LSP imaging at 3T. Materials and MethodsTwenty-four healthy subjects (10 men, 14 women; mean age, 42.2 years; range, 24 -69 years) underwent high-spatial-resolution T2-weighted 3D DW-SSFP imaging with a generalized autocalibrating partially parallel acquisition (GRAPPA) technique on a clinical 3T MR imager (Trio; Siemens Medical Solutions, Erlangen, Germany) with 2-element circularly polarized (CP) phased-array body coils combined with CP phased-array spinal coils.After optimization of the sequence in 3 healthy subjects (1 woman and 2 men, 30 -36 years of age), we used the following parameters: TR/TE, 14.16/4.61 ms; flip angle, 30°; FOV, 360 mm; matrix, 512 ϫ 512; bandwidth, 184 Hz per pixel; fat suppression, water excitation technique; diffusion moments, 90 mT/m (*)msec; 3D slab thickness, 256 mm; voxel dimension, 0.8 ϫ 0.8 ϫ 0.8 mm (320 partitions); number of acquisitions, 1; acquisition time, 10 minutes 49 seconds. The diagram of the 3D DW-SSFP sequence used in this study is shown in Fig 1. The postprocessing techniques, including maximum intensity projection and mul...