Benefits of higher magnetic fields for diffusion tensor imaging (DTI) based on single-shot STEAM MRI sequences: In vivo mouse brain studies at 2.35 T and 7 T

Introduction In theory, the NMR signal is expected to scale more than linearly with magnetic field strength [1]. On the other hand, practical MRI applications such as diffusion tensor imaging (DTI) using echo-planar imaging (EPI) are also affected by a marked reduction of T2 and T2* relaxation times, the latter referring to enhanced magnetic field inhomogeneities with corresponding geometric distortions and signal losses. Because of the physical nature of radiofrequency-refocused echoes as opposed to gradient echoes, single-shot STEAM MRI sequences [2-4] are immune to these effects and may exploit the full advantage of the increased longitudinal magnetization and prolonged T1 relaxation times at higher fields. The purpose of this study was to experimentally confirm and quantify putative gains by comparing maps of the fractional anisotropy and main diffusion direction of mouse brain in vivo obtained by half Fourier (HF) diffusion-weighted (DW) single-shot STEAM MRI at 2.35 T and 7 T.