1D-spectral editing and 2D multispectral in vivo 1 H-MRS and 1 H-MRSI - Methods and applications

Abstract

This article reviews the methodological aspects of detecting low-abundant J-coupled metabolites via 1D spectral editing techniques and 2D nuclear magnetic resonance (NMR) methods applied in vivo, in humans, with a focus on the brain. A brief explanation of the basics of J-evolution will be followed by an introduction to 1D spectral editing techniques (e.g., J-difference editing, multiple quantum coherence filtering) and 2D-NMR methods (e.g., correlation spectroscopy, J-resolved spectroscopy). Established and recently developed methods will be discussed and the most commonly edited J-coupled metabolites (e.g., neurotransmitters, antioxidants, onco-markers, and markers for metabolic processes) will be briefly summarized along with their most important applications in neuroscience and clinical diagnosis.

Big GABA: Edited MR spectroscopy at 24 research sites

“…In contrast, associations between metabolite measurements, or their uncertainty, and SNR and/or linewidth are widely observed in investigations of linear combination modeling of unedited spectra (Bartha et al, 2007; Kanowski et al, 2004; Near et al, 2013a). With spectral editing, the goal is to attain an unambiguously resolved signal that allows for simple peak fitting and integration (Bogner et al, 2016; Harris et al, 2017), but with (short-TE) unedited spectra quantification is based on linear-combination fitting, the outcome of which depends on the degree of orthogonality of the basis-set, which itself depends on data quality (Graveron-Demilly, 2014). Although edited MRS of lower-concentration metabolites typically necessitates comparatively longer scan durations or larger voxels to achieve reasonable SNR, the advent of multiplexed editing (Chan et al, 2016, 2017a, 2017b; Oeltzschner et al, 2017; Saleh et al, 2016) and development of edited MRSI (Bogner et al, 2014; Hnilicová et al, 2016; Zhu et al, 2011) continues to improve the efficiency of spectral editing approaches.…”

Theoretical description of modern1H in Vivo magnetic resonance spectroscopic pulse sequences

“…Recent reviews have covered editing, provided practical guides for high‐field spectroscopy, and recommendations for experimental and analysis details based on consensus . No recent review, however, has provided an in‐depth analysis and comparison of all commonly used MRS pulse sequences and their potential applications beyond standard concentration estimation.…”

“…For intuitively understanding a pulse sequence, the full density matrix formalism provides little insight, as the results of sequences are computed numerically, whereas the product operator formalism, although not strictly valid because it assumes ideal pulses and weak coupling, can be used to obtain a deep understanding of the mechanisms by which complex modern MRS pulse sequences operate. Readers who wish to familiarize themselves with the product operator and density matrix formalisms are directed to the comprehensive textbook Spin Dynamics or other review articles that cover the topic in further depth . As the purpose of this article is to provide insight into modern MRS sequences, the product operator formalism is the natural choice.…”

“…To alleviate the long acquisition time necessitated by phase encoding in two dimensions, MRSI has been combined with parallel imaging techniques such as sensitivity encoding (SENSE) and generalized autocalibrating partially parallel acquisitions (GRAPPA). For an in‐depth discussion into MRSI acquisition, reconstruction, and applications, the reader is directed to imaging‐focused reviews …”

Two-Dimensional Proton Magnetic Resonance Spectroscopy versus J-Editing for GABA Quantification in Human Brain: Insights from a GABA-Aminotransferase Inhibitor Study

“…DQF 1 H MRS in human brain have largely been limited to methods development in healthy controls, although applications in patients with seizure disorders have been reported 26,27 . Technical details regarding MQC spin dynamics and DQF pulse sequences can be found elsewhere 28 .…”