Respiration‐induced movement of the chest wall and internal organs causes temporal B ₀ variations extending throughout the brain. This study demonstrates that these variations can cause significant artifacts in maps obtained at 7 T with the Bloch–Siegert shift (BSS) mapping technique. To suppress these artifacts, a navigator correction scheme was proposed. Two sets of experiments were performed. In the first set of experiments, phase shifts induced by respiration‐related B ₀ variations were assessed for five subjects at 7 T by using a gradient echo (GRE) sequence without phase‐encoding. In the second set of experiments, maps were acquired using a GRE‐based BSS pulse sequence with navigator echoes. For this set, the measurements were consecutively repeated 16 times for the same imaging slice. These measurements were averaged to obtain the reference map. Due to the periodicity of respiration‐related phase shifts, their effect on the reference map was assumed to be negligible through averaging. The individual maps of the 16 repetitions were calculated with and without using the proposed navigator scheme. These maps were compared with the reference map. The peak‐to‐peak value of respiration‐related phase shifts varied between subjects. Without navigator correction, the interquartile range of percentage error in varied between 4.0% and 8.3% among subjects. When the proposed navigator scheme was used, these numbers were reduced to 2.5% and 2.9%, indicating an improvement in the precision of GRE‐based BSS mapping at high magnetic fields.

中文翻译：

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在基于 Bloch-Siegert 位移的人脑 B1+ 图中展示和抑制与呼吸相关的伪影。

呼吸引起的胸壁和内脏器官的运动导致在整个大脑中延伸的时间B ₀变化。这项研究表明，这些变化会导致使用 Bloch-Siegert 位移 (BSS)映射技术在 7 T 下获得的地图中出现明显的伪影。为了抑制这些伪影，提出了导航器校正方案。进行了两组实验。在第一组实验中，通过使用没有相位编码的梯度回波 (GRE) 序列，在 7 T 时评估了由呼吸相关的B ₀变化引起的相移。在第二组实验中，使用带有导航回波的基于 GRE 的 BSS 脉冲序列获取地图。对于这组，对同一成像切片连续重复测量 16 次。这些测量值被平均以获得参考图。由于呼吸相关相移的周期性，假设它们对参考图的影响通过平均可以忽略不计。使用和不使用建议的导航器方案计算 16 次重复的各个地图。这些地图与参考地图进行了比较。呼吸相关相移的峰峰值因受试者而异。没有导航器校正，百分比误差的四分位间距受试者之间的差异在 4.0% 和 8.3% 之间。当使用建议的导航器方案时，这些数字减少到 2.5% 和 2.9%，表明在高磁场下基于 GRE 的 BSS映射精度有所提高。