Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, USA; F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
Division of Biomedical Engineering, Department of Human Biology, University of Cape Town, Cape Town, South Africa.
Neuroimage. 2019 May 1;191:537-548. doi: 10.1016/j.neuroimage.2019.02.059. Epub 2019 Mar 3.
Accurate and reliable quantification of brain metabolites measured in vivo using H magnetic resonance spectroscopy (MRS) is a topic of continued interest. Aside from differences in the basic approach to quantification, the quantification of metabolite data acquired at different sites and on different platforms poses an additional methodological challenge. In this study, spectrally edited γ-aminobutyric acid (GABA) MRS data were analyzed and GABA levels were quantified relative to an internal tissue water reference. Data from 284 volunteers scanned across 25 research sites were collected using GABA+ (GABA + co-edited macromolecules (MM)) and MM-suppressed GABA editing. The unsuppressed water signal from the volume of interest was acquired for concentration referencing. Whole-brain T-weighted structural images were acquired and segmented to determine gray matter, white matter and cerebrospinal fluid voxel tissue fractions. Water-referenced GABA measurements were fully corrected for tissue-dependent signal relaxation and water visibility effects. The cohort-wide coefficient of variation was 17% for the GABA + data and 29% for the MM-suppressed GABA data. The mean within-site coefficient of variation was 10% for the GABA + data and 19% for the MM-suppressed GABA data. Vendor differences contributed 53% to the total variance in the GABA + data, while the remaining variance was attributed to site- (11%) and participant-level (36%) effects. For the MM-suppressed data, 54% of the variance was attributed to site differences, while the remaining 46% was attributed to participant differences. Results from an exploratory analysis suggested that the vendor differences were related to the unsuppressed water signal acquisition. Discounting the observed vendor-specific effects, water-referenced GABA measurements exhibit similar levels of variance to creatine-referenced GABA measurements. It is concluded that quantification using internal tissue water referencing is a viable and reliable method for the quantification of in vivo GABA levels.
使用 H 磁共振波谱（MRS）对体内测量的脑代谢物进行准确可靠的定量是一个持续关注的话题。除了定量方法的基本差异外，在不同地点和不同平台上获得的代谢物数据的定量还带来了额外的方法学挑战。在这项研究中，对光谱编辑的γ-氨基丁酸（GABA）MRS 数据进行了分析，并相对于内部组织水参考定量了 GABA 水平。使用 GABA+（GABA + 共编辑大分子（MM））和 MM 抑制 GABA 编辑，在 25 个研究地点从 284 名志愿者中收集了数据。为了进行浓度参考，从感兴趣的体积中获取未被抑制的水信号。采集全脑 T 加权结构图像并进行分割，以确定灰质、白质和脑脊液的体素组织分数。对水参考 GABA 测量值进行了完全校正，以消除与组织相关的信号弛豫和水可见性效应。GABA+数据的全队列变异系数为 17%，MM 抑制 GABA 数据的变异系数为 29%。GABA+数据的平均站点内变异系数为 10%，MM 抑制 GABA 数据的变异系数为 19%。GABA+数据的总方差中有 53%归因于供应商差异，而其余方差归因于站点（11%）和参与者（36%）效应。对于 MM 抑制数据，方差的 54%归因于站点差异，而其余 46%归因于参与者差异。探索性分析的结果表明，供应商差异与未被抑制的水信号采集有关。忽略观察到的供应商特定效应，使用内部组织水参考的 GABA 定量测量表现出与肌酸参考 GABA 定量测量相似的变异性水平。结论是，使用内部组织水参考进行定量是一种可行且可靠的方法，可用于定量体内 GABA 水平。
