Department of Radiology and Biomedical Imaging, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, 06520, USA.
Department of Biomedical Engineering, Magnetic Resonance Research Center, Yale University School of Medicine, New Haven, Connecticut, 06520, USA.
NMR Biomed. 2021 Jan;34(1):e4415. doi: 10.1002/nbm.4415. Epub 2020 Oct 1.
A multitude of extracranial lipid suppression methods exist for proton MRSI acquisitions. Popular and emerging lipid suppression methods each have their inherent set of advantages and disadvantages related to the achievable level of lipid suppression, RF power deposition, insensitivity to B field and lipid T heterogeneity, brain coverage, spatial selectivity, chemical shift displacement (CSD) errors and the reliability of spectroscopic data spanning the observed 0.9-4.7 ppm band. The utility of elliptical localization with pulsed second order fields (ECLIPSE) was previously demonstrated with a greater than 100-fold in extracranial lipid suppression and low power requirements utilizing 3 kHz bandwidth AFP pulses. Like all gradient-based localization methods, ECLIPSE is sensitive to CSD errors, resulting in a modified metabolic profile in edge-of-ROI voxels. In this work, ECLIPSE is extended with 15 kHz bandwidth second order gradient-modulated RF pulses based on the gradient offset-independent adiabaticity (GOIA) algorithm to greatly reduce CSD and improve spatial selectivity. An adiabatic double spin-echo ECLIPSE inner volume selection (TE = 45 ms) MRSI method and an ECLIPSE outer volume suppression (TE = 3.2 ms) FID-MRSI method were implemented. Both GOIA-ECLIPSE MRSI sequences provided artifact-free metabolite spectra in vivo, with a greater than 100-fold in lipid suppression and less than 2.6 mm in-plane CSD and less than 3.3 mm transition width for edge-of-ROI voxels, representing an ~5-fold improvement compared with the parent, nongradient-modulated method. Despite the 5-fold larger bandwidth, GOIA-ECLIPSE only required a 1.9-fold increase in RF power. The highly robust lipid suppression combined with low CSD and sharp ROI edge transitions make GOIA-ECLIPSE an attractive alternative to commonly employed lipid suppression methods. Furthermore, the low RF power deposition demonstrates that GOIA-ECLIPSE is very well suited for high field (≥3 T) MRSI applications.
有许多颅外脂质抑制方法可用于质子 MRSI 采集。流行和新兴的脂质抑制方法各自具有固有的一系列优点和缺点，与可实现的脂质抑制水平、RF 功率沉积、对 B 场和脂质 T 异质性、脑覆盖范围、空间选择性、化学位移位移 (CSD) 误差以及观察到的 0.9-4.7 ppm 带宽内光谱数据的可靠性有关。以前已经证明，使用具有大于 100 倍的颅外脂质抑制和低功率要求的具有脉冲二阶场的椭圆定位 (ECLIPSE) （ECLIPSE）具有更大的实用性，该方法利用 3 kHz 带宽 AFP 脉冲。像所有基于梯度的定位方法一样，ECLIPSE 对 CSD 误差很敏感，导致 ROI 边缘体素的代谢谱发生变化。在这项工作中，基于梯度偏移独立绝热性 (GOIA) 算法，用 15 kHz 带宽的二阶梯度调制 RF 脉冲扩展了 ECLIPSE，以大大降低 CSD 并提高空间选择性。实现了绝热双自旋回波 ECLIPSE 内腔选择 (TE = 45 ms) MRSI 方法和 ECLIPSE 外腔抑制 (TE = 3.2 ms) FID-MRSI 方法。两种 GOIA-ECLIPSE MRSI 序列都在体内提供了无伪影的代谢物谱，颅外脂质抑制率超过 100 倍，边缘 ROI 体素的面内 CSD 小于 2.6 mm，转换宽度小于 3.3 mm，与母代相比，这是一种约 5 倍的改进，非梯度调制方法。尽管带宽大 5 倍，但 GOIA-ECLIPSE 仅需要 1.9 倍的 RF 功率增加。高度稳健的脂质抑制与低 CSD 和锐利的 ROI 边缘过渡相结合，使 GOIA-ECLIPSE 成为常用脂质抑制方法的有吸引力的替代方法。此外，低 RF 功率沉积表明 GOIA-ECLIPSE 非常适合高磁场（≥3 T）MRSI 应用。
