Lange Thomas, Ko Cheng-Wen, Lai Ping-Hong, Dacko Michael, Tsai Shang-Yueh, Buechert Martin
Department of Radiology, Medical Physics, Medical Center-University of Freiburg, Freiburg, Germany.
Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan.
NMR Biomed. 2016 Dec;29(12):1739-1747. doi: 10.1002/nbm.3660. Epub 2016 Oct 25.
Valine and lactate have been recognized as important metabolic markers to diagnose brain abscess by means of MRS. However, in vivo unambiguous detection and quantification is hampered by macromolecular contamination. In this work, MEGA-PRESS difference editing of valine and lactate is proposed. The method is validated in vitro and applied for quantitative in vivo experiments in one healthy subject and two brain abscess patients. It is demonstrated that with this technique the overlapping lipid signal can be reduced by more than an order of magnitude and thus the robustness of valine and lactate detection in vivo can be enhanced. Quantification of the two abscess MEGA-PRESS spectra yielded valine/lactate concentration ratios of 0.10 and 0.27. These ratios agreed with the concentration ratios determined from concomitantly acquired short-T PRESS data and were in line with literature values. The quantification accuracy of lactate (as measured with Cramér-Rao lower bounds in LCModel processing) was better for MEGA-PRESS than for short-T PRESS in all acquired in vivo datasets. The Cramér-Rao lower bounds of valine were only better for MEGA-PRESS in one of the two abscess cases, while in the other case coediting of isoleucine confounded the quantification in the MEGA-PRESS analysis. MEGA-PRESS and short-T PRESS should be combined for unambiguous quantification of amino acids in abscess measurements. Simultaneous valine/lactate MEGA-PRESS editing might benefit the distinction of brain abscesses from tumors, and further categorization of bacteria with reasonable sensitivity and specificity.
缬氨酸和乳酸已被公认为是通过磁共振波谱（MRS）诊断脑脓肿的重要代谢标志物。然而，体内大分子污染阻碍了对它们的明确检测和定量。在这项工作中，提出了缬氨酸和乳酸的MEGA-PRESS差异编辑方法。该方法在体外得到验证，并应用于一名健康受试者和两名脑脓肿患者的体内定量实验。结果表明，通过该技术，重叠的脂质信号可降低一个数量级以上，从而增强体内缬氨酸和乳酸检测的稳健性。对两个脓肿的MEGA-PRESS谱进行定量分析，得到缬氨酸/乳酸浓度比分别为0.10和0.27。这些比值与同时获取的短T PRESS数据确定的浓度比值一致，且与文献值相符。在所有采集的体内数据集中，MEGA-PRESS对乳酸的定量准确性（以LCModel处理中的克拉美-罗下限衡量）优于短T PRESS。缬氨酸的克拉美-罗下限仅在两个脓肿病例中的一个中MEGA-PRESS更好，而在另一个病例中，异亮氨酸的共同编辑在MEGA-PRESS分析中混淆了定量。在脓肿测量中，应将MEGA-PRESS和短T PRESS结合起来以明确氨基酸的定量。缬氨酸/乳酸同时进行MEGA-PRESS编辑可能有助于区分脑脓肿和肿瘤，并以合理的敏感性和特异性对细菌进行进一步分类。
