title: Simultaneous detection of valine and lactate using MEGA-PRESS editing in pyogenic brain abscess.
abstract: 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-TEPRESS 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-TEPRESS 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-TEPRESS 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.
authors: Department of Radiology, Medical Physics, Medical Center-University of Freiburg, Freiburg, Germany.
authors: Thomas
authors: T
authors: Lange
authors: Department of Computer Science and Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan.
authors: Cheng-Wen
authors: CW
authors: Ko
authors: Department of Radiology, Kaohsiung Veterans General Hospital, Kaohsiung, Taiwan.
authors: Ping-Hong
authors: PH
authors: Lai
authors: Department of Radiology, Medical Physics, Medical Center-University of Freiburg, Freiburg, Germany.
authors: Michael
authors: M
authors: Dacko
authors: Graduate Institute of Applied Physics, National Chengchi University, Taipei, Taiwan.|Research Center for Mind, Brain and Learning, National Chengchi University, Taipei, Taiwan.
authors: Shang-Yueh
authors: SY
authors: Tsai
authors: Department of Radiology, Medical Physics, Medical Center-University of Freiburg, Freiburg, Germany.
authors: Martin
authors: M
authors: Buechert
mesh_terms: D000465:Algorithms; D015415:Biomarkers / Q000378:metabolism; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D001922:Brain Abscess / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D057054:Molecular Imaging / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D014633:Valine / Q000378:metabolism*
chemical_list: D015415:Biomarkers; D019344:Lactic Acid; D014633:Valine
keywords: MEGA-PRESS; brain abscess; difference editing; lactate; lipid contamination; valine