人脑GABA磁共振波谱测量中大分子影响的研究

Effects of Macromolecules on Cerebral GABA Measurements Using Magnetic Resonance Spectroscopy

J差分谱编辑技术已广泛用于人脑g-氨基丁酸(γ-amino butyric acid,GABA)的检测,利用MEGA-PRESS序列可以有效编辑GABA在δ_H 3.02处的信号.由于相近的化学位移和J耦合作用,大分子(macromolecule,MM)在δ_H 3.00的信号也同时被编辑,因此测量得到的GABA信号中包含一部分MM信号(GABA+MM,简称GABA+).对称谱编辑技术可以有效抑制大分子,但该方法对编辑脉冲的频率选择性要求较高,因此对称谱编辑技术中编辑脉冲持续时间一般较长.该研究将MEGA-PRESS序列中编辑脉冲持续时间由14 ms增加到20 ms,回波时间(echo time,TE)由68 ms增加到80 ms,分别测量GABA+与对称谱编辑技术抑制大分子后的GABA(简称GABA).结果发现,在较长编辑脉冲作用时间和较长TE条件下,GABA比GABA+含量低27%;长编辑脉冲持续时间可以有效提高编辑脉冲的频率选择性,更好地实现对称谱编辑技术抑制大分子,有助于分析人脑GABA含量测定中大分子信号干扰的影响.纯GABA含量测量,有助于更准确地分析GABA在人脑中的代谢过程,以及GABA含量与各种疾病和功能认知反应之间的相关性.

The MEGA-PRESS sequence has been widely used to measure the δH 3.02 γ-amino butyric acid （GABA） signal by J-difference editing. However, the sequence cannot eliminate the macromolecule signals at the same chemical shift completely. Symmetrical editing can be applied to suppress the macromolecule signals. However, the approach is rarely applied at field strength of 3 T due to insufficient frequency selectivity of the editing pulse. In this study, GABA＋（i.e., GABA＋macromolecules） and macromolecule-suppressed GABA signals in the occipital lobe of human subjects were measured with symmetrical editing at 3 T. The duration of the editing pulse was increased from 14 ms to 20 ms to improve frequency selectivity, and echo time （TE） from 68 ms to 80 ms. It was found that the fraction of the total signal retained following macromolecule suppression （[GABA]/[GABA＋]） was 0.73. It is concluded that symmetric macromoleculesuppressed editing can be used to acquire macromolecule-suppressed GABA signals, and may serve as a better tool to assess inter-individual differences in cerebral GABA level.