Bednařík Petr, Moheet Amir, Deelchand Dinesh K, Emir Uzay E, Eberly Lynn E, Bareš Martin, Seaquist Elizabeth R, Öz Gülin
Center for Magnetic Resonance Research, Department of Radiology, Medical School, University of Minnesota, Minneapolis, MN, USA.
Division of Endocrinology and Diabetes, Department of Medicine, University of Minnesota, Minneapolis, MN, USA.
NMR Biomed. 2015 Jun;28(6):685-93. doi: 10.1002/nbm.3309. Epub 2015 Apr 22.
Hippocampal dysfunction is known to be associated with several neurological and neuropsychiatric disorders such as Alzheimer's disease, epilepsy, schizophrenia and depression; therefore, there has been significant clinical interest in studying hippocampal neurochemistry. However, the hippocampus is a challenging region to study using (1) H MRS, hence the use of MRS for clinical research in this region has been limited. Our goal was therefore to investigate the feasibility of obtaining high-quality hippocampal spectra that allow reliable quantification of a neurochemical profile and to establish inter-session reproducibility of hippocampal MRS, including reproducibility of voxel placement, spectral quality and neurochemical concentrations. Ten healthy volunteers were scanned in two consecutive sessions using a standard clinical 3 T MR scanner. Neurochemical profiles were obtained with a short-echo (T(E) = 28 ms) semi-LASER localization sequence from a relatively small (4 mL) voxel that covered about 62% of the hippocampal volume as calculated from segmentation of T1 -weighted images. Voxel composition was highly reproducible between sessions, with test-retest coefficients of variation (CVs) of 3.5% and 7.5% for gray and white matter volume fraction, respectively. Excellent signal-to-noise ratio (54 based on the N-acetylaspartate (NAA) methyl peak in non-apodized spectra) and linewidths (~9 Hz for water) were achieved reproducibly in all subjects. The spectral quality allowed quantification of NAA, total choline, total creatine, myo-inositol and glutamate with high scan-rescan reproducibility (CV ≤ 6%) and quantification precision (Cramér-Rao lower bound, CRLB < 9%). Four other metabolites, including glutathione and glucose, were quantified with scan-rescan CV below 20%. Therefore, the highly optimized, short-echo semi-LASER sequence together with FASTMAP shimming substantially improved the reproducibility and number of quantifiable metabolites relative to prior reports. In addition, the between-session variation in metabolite concentrations, as well as CRLB, was lower than the between-subject variation of the concentrations for most metabolites, indicating that the method has the sensitivity to detect inter-individual differences in the healthy brain.
已知海马体功能障碍与多种神经和神经精神疾病相关，如阿尔茨海默病、癫痫、精神分裂症和抑郁症；因此，研究海马体神经化学引起了临床的极大兴趣。然而，海马体是一个使用氢磁共振波谱（1H MRS）进行研究具有挑战性的区域，因此该技术在该区域的临床研究应用一直有限。因此，我们的目标是研究获取高质量海马体波谱的可行性，该波谱能够可靠地定量神经化学特征，并建立海马体MRS的不同扫描间可重复性，包括体素定位、波谱质量和神经化学浓度的可重复性。使用标准临床3T磁共振扫描仪对10名健康志愿者进行了连续两次扫描。通过短回波（T(E)=28ms）半激光定位序列，从一个相对较小（约4mL）的体素中获取神经化学特征，该体素覆盖了根据T1加权图像分割计算得出的约62%的海马体体积。不同扫描间体素组成具有高度可重复性，灰质和白质体积分数的重测变异系数（CVs）分别为3.5%和7.5%。所有受试者均能重复获得优异的信噪比（基于未加窗波谱中的N-乙酰天门冬氨酸（NAA）甲基峰约为54）和线宽（水约为9Hz）。波谱质量允许对NAA、总胆碱、总肌酸、肌醇和谷氨酸进行定量，具有高扫描-重测可重复性（CV≤6%）和定量精度（克拉美-罗下限，CRLB<9%）。包括谷胱甘肽和葡萄糖在内的其他四种代谢物，扫描-重测CV低于20%。因此，相对于先前的报道，高度优化的短回波半激光序列与FASTMAP匀场技术显著提高了可重复性和可定量代谢物的数量。此外，大多数代谢物的扫描间代谢物浓度变化以及CRLB低于个体间浓度变化，表明该方法具有检测健康大脑个体间差异的灵敏度。
