Purpose

The purpose of this study was to characterize the individual contribution of multiple fat peaks to the measured chemical exchange saturation transfer (CEST) signal when using water-selective binomial-pulse excitation and to determine the effects of multiple fat peaks in the presence of B₀ inhomogeneity.

Methods

The excitation profiles of multiple binomial pulses were simulated. A CEST sequence with binomial-pulse excitation and modified point-resolved spectroscopy localization was then applied to the in vivo lumbar spinal vertebrae to determine the signal contributions of three distinct groups of lipid resonances. These confounding signal contributions were measured as a function of the irradiation frequency offset to determine the effect of the multi-peak nature of the fat signal on CEST imaging of exchange sites (at 1.0, 2.0 and 3.5 ppm) and robustness in the presence of B₀ inhomogeneity.

Results

Numerical simulations and in vivo experiments showed that water excitation (WE) using a 1-3-3-1 (WE-4) pulse provided the broadest signal suppression, which provided partial robustness against B₀ inhomogeneity effects. Confounding fat signal contributions to the CEST contrasts at 1.0, 2.0 and 3.5 ppm were unavoidable due to the multi-peak nature of the fat signal. However, these CEST sites only suffer from small lipid artifacts with ∆B₀ spanning roughly from − 50 to 50 Hz. Especially for the CEST site at 3.5 ppm, the lipid artifacts are smaller than 1% with ∆B₀ in this range.

Conclusion

In WE-4-based CEST magnetic resonance imaging, B₀ inhomogeneity is the limiting factor for fat suppression. The CEST sites at 1.0, 2.0 ppm and 3.5 ppm unavoidably suffer from lipid artifacts. However, when the ∆B₀ is confined to a limited range, these CEST sites are only affected by small lipid artifacts, which may be ignorable in some cases of clinical applications.

中文翻译：

---

在化学交换饱和转移 (CEST) 磁共振成像中使用水选择性二项式脉冲激发抑制脂肪的有效性。

目的

本研究的目的是在使用水选择性二项式脉冲激发时表征多个脂肪峰对测量的化学交换饱和转移 (CEST) 信号的个体贡献，并确定在B ₀存在下多个脂肪峰的影响不均匀性。

方法

模拟了多个二项式脉冲的激发曲线。然后将具有二项式脉冲激发和改进的点分辨光谱定位的 CEST 序列应用于体内腰椎，以确定三个不同组的脂质共振的信号贡献。这些混杂的信号贡献被测量为辐射频率偏移的函数，以确定脂肪信号的多峰性质对交换位点的 CEST 成像（在 1.0、2.0 和 3.5 ppm）和存在B 时的稳健性的影响₀不均匀性。

结果

数值模拟和体内实验表明，使用 1-3-3-1 (WE-4) 脉冲的水激发 (WE) 提供了最广泛的信号抑制，这提供了对B ₀不均匀性影响的部分鲁棒性。由于脂肪信号的多峰性质，在 1.0、2.0 和 3.5 ppm 处对 CEST 对比度的混杂脂肪信号贡献是不可避免的。然而，这些 CEST 位点仅受到小脂质伪影的影响，ΔB ₀范围大致从 - 50 到 50 Hz。特别是对于 3.5 ppm 的 CEST 位点，在此范围内的ΔB _{0 时}，脂质伪影小于 1% 。

结论

在基于 WE-4 的 CEST 磁共振成像中，B ₀不均匀性是脂肪抑制的限制因素。1.0、2.0 ppm 和 3.5 ppm 的 CEST 位点不可避免地受到脂质伪影的影响。然而，当∆B ₀被限制在一个有限的范围内时，这些 CEST 位点仅受小的脂质伪影影响，这在某些临床应用情况下可能可以忽略不计。