Reliable Cortical Thickness Estimation with Reduction of Susceptibility-Induced Signal Loss using Optimized T1-Weighted Single-Slab 3D Turbo Spin Echo Pulse Sequence

Introduction: In brain volumetry, magnetization-prepared rapid gradient recalled echo (MP-RAGE) imaging [1], which yields a strong T1-weighted contrast among brain tissues and thus a highly accurate segmentation of the brain structures, has been widely used. However, since signals in MPRAGE result from free induction decay (FID) without radio-frequency (RF) pulse induced refocusing, conventional MP-RAGE is sensitive to susceptibilityinduced magnetic field inhomogeneities, yielding loss of signals or image distortions and thereby impairing the accuracy of cortical thickness measurement. As an alternative to conventional MP-RAGE, T1-optimized, single-slab three-dimensional (3D) turbo/fast spin echo (SE) imaging [2], which employs a long refocusing pulse train with variable flip angles followed by a flip-down restore pulse train for contrast manipulation, is recently introduced and known to be resistant to local field variations. Thus, the purpose of this work is to investigate the feasibility of the proposed, single-slab 3D fast/turbo SE imaging for reliable, accurate estimation of cortical thickness, particularly for prefrontal and temporal lobes, which are the regions heavily affected by the susceptibility-induced field variations.