γ-氨基丁酸(GABA)在人腦的主要抑制性神經傳遞物質，並在中樞神經系統中扮演重要的角色。磁共振頻譜(1H MRS）是一種非侵入性工具，提供體內代謝濃度的測量。然而，由於GABA的濃度人類大腦僅毫莫耳以及其磁共振頻譜與來自其他信號強烈的代謝物共振的頻率重疊。最常見的檢測GABA的序列是使用MEshcher–GArwood Point RESolved Spectroscopy（MEGA-PRESS），這是基於PRESS序列頻譜編輯的方法。在這項研究中，我們比較了使用四種不同的相位循環機制（w/o PC，PC4，PC16和Inter4）所得到的編輯頻普品質，區域包括背外側前額葉皮層（DLPFC）和前扣帶皮層（ACC）。結論部分，我們的結果表明，在使用MEGA-PRESS編輯頻譜觀測GABA時，加入相位循環是必要的，能確保獲得穩定的GABA頻譜形狀以利於濃度的定量。然而，當平均頻率漂移越大，可能發生相減誤差，因此的相位循環次數越低則可避免相減誤差。

GABA (γ-Aminobutyric acid) as a major inhibitory neurotransmitter in human brain plays an important role in central nervous system. Proton Magnetic Resonance Spectroscopy (1H MRS) is a non-invasively tool that provides measurement of in vivo metabolic concentrations. However, GABA is only present in human brain at millimolar levels and its resonance frequency overlaps with other metabolites having over 100 times higher signals than GABA. The most common method used to detect GABA is MEshcher–GArwood Point RESolved Spectroscopy (MEGA-PRESS) which is a spectral editing MRS method. In this study, we compared the spectral quality of GABA using 4 kinds of phase cycling schemes (w/o PC, PC4, PC16 and Inter4) in dorsal lateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC). In conclusions, our results showed that phase cycling is necessary for MEGA-PRESS to ensure stable GABA shape. However, subtraction artifacts may occur at the presence of frequency drift between edit on and edit off spectra, so lower phase cycling steps are suggested to ensure GABA spectral quality and to avoid subtraction artifacts

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