Vanderbilt University Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, Tennessee, USA.
Magn Reson Med. 2024 Mar;91(3):886-895. doi: 10.1002/mrm.29933. Epub 2023 Nov 27.
Application of highly selective editing RF pulses provides a means of minimizing co-editing of contaminants in J-difference MRS (MEGA), but it causes reduction in editing yield. We examined the flip angles (FAs) of narrow-band editing pulses to maximize the lactate edited signal with minimal co-editing of threonine.
The effect of editing-pulse FA on the editing performance was examined, with numerical and phantom analyses, for bandwidths of 17.6-300 Hz in MEGA-PRESS editing of lactate at 3T. The FA and envelope of 46 ms Gaussian editing pulses were tailored to maximize the lactate edited signal at 1.3 ppm and minimize co-editing of threonine. The optimized editing-pulse FA MEGA scheme was tested in brain tumor patients.
Simulation and phantom data indicated that the optimum FA of MEGA editing pulses is progressively larger than 180° as the editing-pulse bandwidth decreases. For 46 ms long 17.6 Hz bandwidth Gaussian pulses and other given sequence parameters, the lactate edited signal was maximum at the first and second editing-pulse FAs of 241° and 249°, respectively. The edit-on and difference-edited lactate peak areas of the optimized FA MEGA were greater by 43% and 25% compared to the 180°-FA MEGA, respectively. In-vivo data confirmed the simulation and phantom results. The lesions of the brain tumor patients showed elevated lactate and physiological levels of threonine.
The lactate MEGA editing yield is significantly increased with editing-pulse FA much larger than 180° when the editing-pulse bandwidth is comparable to the lactate quartet frequency width.
高选择性编辑射频脉冲的应用提供了一种最小化 J 差 MRS（MEGA）中污染物共编辑的方法，但会导致编辑产率降低。我们研究了窄带编辑脉冲的翻转角（FA），以在最小化苏氨酸共编辑的情况下最大化乳酸编辑信号。
通过数值和体模分析，研究了在 3T 下 MEGA-PRESS 编辑乳酸时，编辑脉冲带宽为 17.6-300 Hz 时编辑脉冲 FA 对编辑性能的影响。编辑脉冲的 FA 和包络被调整为 46 ms 高斯编辑脉冲，以在 1.3 ppm 处最大化乳酸编辑信号，并最小化苏氨酸的共编辑。优化后的编辑脉冲 FA MEGA 方案在脑肿瘤患者中进行了测试。
模拟和体模数据表明，随着编辑脉冲带宽的减小，MEGA 编辑脉冲的最佳 FA 逐渐大于 180°。对于 46 ms 长的 17.6 Hz 带宽高斯脉冲和其他给定的序列参数，乳酸编辑信号在第一和第二编辑脉冲 FA 分别为 241°和 249°时最大。与 180° FA MEGA 相比，优化 FA MEGA 的编辑 ON 和差异编辑乳酸峰面积分别增加了 43%和 25%。体内数据证实了模拟和体模结果。脑肿瘤患者的病变显示出升高的乳酸和生理水平的苏氨酸。
当编辑脉冲带宽与乳酸四重峰宽度相当时，编辑脉冲 FA 远大于 180°时，乳酸 MEGA 编辑产率显著增加。
