An optimized semi‐LASER sequence that is capable of acquiring artefact‐free data with an echo time (TE) of 20.1 ms on a standard clinical 3 T MR system was developed. Simulations were performed to determine the optimal TEs that minimize the expected Cramér‐Rao lower bound (CRLB) as proxy for quantification accuracy of metabolites. Optimized RF pulses, crusher gradients and phase cycling were used to achieve the shortest TE in a semi‐LASER sequence to date on a clinical system. Synthetic spectra were simulated using the density matrix formalism for TEs spanning from 20.1 to 220.1 ms. These simulations were used to calculate the expected CRLB for each of the 18 metabolites typically considered in ¹H MRS. High quality spectra were obtained in six healthy volunteers in the prefrontal cortex, which is known for spurious echoes due to its proximity to the paranasal sinuses, and in the parietal‐occipital cortex. Spectral transients were sufficient in quality to enable phase and frequency alignment prior to summation over all repetitions. Automated high‐quality water suppression was obtained for all voxels without manual adjustment. The shortest TE minimized the CRLB for all brain metabolites except glycine due to its overlap with myo‐inositol at this TE. It is also demonstrated that the CRLBs increase rapidly with TE for certain coupled metabolites.

中文翻译：

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半激光、单体素光谱序列，在 3 T 时在人脑中的最小回波时间为 20.1 ms。

开发了一种优化的半激光序列，能够在标准临床 3 T MR 系统上以 20.1 ms 的回波时间 (TE) 获取无伪影数据。进行模拟以确定将预期的 Cramér-Rao 下限 (CRLB) 最小化的最佳 TE，作为代谢物定量准确性的代表。迄今为止，在临床系统上，优化的射频脉冲、破碎机梯度和相位循环用于在半激光序列中实现最短的 TE。使用跨度为 20.1 到 220.1 ms 的 TE 的密度矩阵形式来模拟合成光谱。这些模拟用来计算预期的CRLB对于每个18种代谢物典型地在考虑¹H 夫人。在前额叶皮层的六名健康志愿者中获得了高质量的光谱，前额叶皮层因其靠近鼻窦和顶枕叶皮层而以虚假回声而闻名。频谱瞬变的质量足以在所有重复求和之前实现相位和频率对齐。无需手动调整即可获得所有体素的自动高质量水抑制。最短的 TE 使除甘氨酸之外的所有脑代谢物的 CRLB 最小化，因为它在该 TE 与肌醇重叠。还表明某些偶联代谢物的 CRLB 随 TE 迅速增加。