Fast Single Breath-hold 3D Abdominal Spiral Imaging with Water / Fat Separation and Off-resonance Correction

Introduction Large volume coverage, short total scan time and robust water/fat separation are important issues in abdominal MRI. Breath-hold approaches are often used to avoid respiratory motion artifacts, which demands for efficient sampling schemes. Spiral imaging is one of them [1], but shows high sensitivity to off-resonance [2]. Image blurring resulting from spatially varying Bo inhomogeneities and chemical shift composition can degrade image quality seriously. If both effects are separable, correction can potentially be done. Three-point chemical-shift imaging, in particular IDEAL [3], was found to achieve high quality water/fat separation, delivering a ΔBo map as a byproduct. Recently, Brodsky et al. [4] proposed to use this additional information for non-Cartesian water/fat imaging. In this work this concept was applied to 3D single breath-hold water/fat resolved, off-resonance corrected spiral imaging using the stack of spirals approach. Parallel imaging was employed to improve SNR, sampling efficiency and to achieve an up-front data compression during image reconstruction reducing IDEAL reconstruction time, opening new applications for self-referenced non-Cartesian MRI. Theory For a chemical shift encoded spiral gradient echo scan using a fixed k-space trajectory, the sampled receiver signal sn(t) of the n different echoes centered at TEn, can be given as: sn(t) = ∑j [ ∫ ρj(r) exp(ik(t)r) exp(iγΔBo(r)t) exp(iγΔBo(r)TEn) exp(iωjt) dr ] exp(iωjTEn)