Diffusion weighted MR nerve sheath imaging (DW-NSI) using diffusion-sensitized driven-equiliblium (DSDE)

INTRODUCTION: The use of diffusion-weighted imaging (DWI) for the evaluation of peripheral nerves was recently introduced by Takahara et al. [1]. Since the signal from the nerves at DWI originates from water within the nerve sheath, this method can be referred to as diffusion-weighted nerve sheath imaging (DW-NSI). There are two major limitations related to echo-planar imaging (EPI)-based DW-NSI: 1) anatomical position shift due to B0 inhomogeneity, and 2) signal discontinuity or inhomogeneity due to axial slice acquisition even though coronally reformatted images are used for reading. The reasons for axial-based acquisition are severe susceptibility and B0 inhomogeneity effects on direct coronal images. The socalled “diffusion-prepared” sequence, also known as driven-equilibrium (DE) Fourier transform (DEFT), was proposed in the early 1990s [2,3]. Since it does not employ EPI but gradient-echo readout, image distortion can largely be prevented making direct coronal imaging feasible. Recently, this preparation concept has been applied for blood signal suppression using smaller sensitizing gradients, which is called motion-sensitized drivenequilibrium (MSDE) [4,5], and several optimizations were proposed [6,7]. The purposes of this study were to assess the utility of the latest MSDE preparation design but with larger sensitizing gradients for DW-NSI, and to compare this new approach to the conventional EPI approach for DWNSI, at 3.0T. In line with the name MSDE, we called the proposed DEFT technique “diffusion-sensitized driven-equilibrium“ (DSDE).