Wilman A H, Allen P S
Department of Physics, University of Alberta, Edmonton, Canada.
J Magn Reson B. 1996 Dec;113(3):203-13. doi: 10.1006/jmrb.1996.0178.
The approximately 2.6 ppm aspartate multiplet of N-acetyl aspartate (NAA) is considered a potential source of additional information on N-acetyl aspartate in vivo. Because the aspartate multiplet is the AB part of a strongly coupled ABX system it gives rise, as is shown in the analysis presented, to a significant field-strength dependence in the echo-time-dependent modulations of the response to typical spatial-localization sequences. The echo-time dependence of this response is developed analytically, not only for the STEAM and the PRESS localization sequences, but also for a spin-echo sequence. It is then verified experimentally at 2.35 T. The field-strength dependence of the response is demonstrated by evaluating the changes in the echo-time-dependent responses to each of the three sequences at field strengths of 1.5, 2.35, and 4.0 T. By means of these results, the preferred sequence (PRESS) can be optimized for the NAA aspartate multiplet at each field strength, as is illustrated with the human brain spectra obtained in vivo at 1.5 T. These in vivo spectra compare the optimal, long TE timing (163 ms) with a suboptimal TE (70 ms), for the observation of the approximately 2.6 ppm aspartate resonances of NAA.
N - 乙酰天门冬氨酸（NAA）约2.6 ppm的天门冬氨酸多重峰被认为是获取体内N - 乙酰天门冬氨酸额外信息的潜在来源。由于天门冬氨酸多重峰是强耦合ABX系统的AB部分，如所呈现的分析所示，它在对典型空间定位序列的响应的回波时间依赖性调制中会产生显著的场强依赖性。这种响应的回波时间依赖性不仅针对STEAM和PRESS定位序列进行了分析推导，还针对自旋回波序列进行了推导。然后在2.35 T下进行了实验验证。通过评估在1.5、2.35和4.0 T场强下对这三个序列中每个序列的回波时间依赖性响应的变化，证明了响应的场强依赖性。借助这些结果，可以针对每个场强对NAA天门冬氨酸多重峰的首选序列（PRESS）进行优化，如在1.5 T下体内获得的人脑谱图所示。这些体内谱图比较了用于观察NAA约2.6 ppm天门冬氨酸共振的最佳长TE定时（163 ms）和次优TE（70 ms）。
