Proton spectral editing for discrimination of lactate and threonine 1.31 ppm resonances in human brain in vivo

Abstract

Prior 1 H MRS measurements of lactate (Lac) in human brain in vivo commonly focused on the methyl proton resonance at 1.31 ppm. These methyl protons are scalarly coupled to a methine proton resonating at 4.10 ppm, with strength of 6.93 Hz (pH neutral) (1). For detection of this low-concentration metabolite, a doublet at 1.31 ppm is often targeted with either a short TE (2) or an optimized long TE (3) to minimize the spectral overlap with lipid signals. The overlapping interference can be further reduced by spectral editing using, e.g., J-difference spectroscopy (4), multiple-quantum filtering (5), or a postacquisition processing filter (6).Threonine (Thr) is present in autopsied human brain tissue (7) and has been detected in rat brain (8,9) and human brain (10) by 1 H MRS. Thr has five water nonexchangeable protons from a methyl group and two methine groups, forming an A 3 MX spin system, where A, M, and X spins resonate at 1.31, 4.25, and 3.58 ppm, respectively, with coupling strengths J AM ϭ 6.35 Hz and J MX ϭ 4.92 Hz (1). Because of the close proximity of the A-spin resonances of Lac and Thr, detection of the signal at 1.31 ppm by conventional MRS always records an overlap of Lac and Thr, as illustrated in Fig. 1a. Furthermore, unless account is taken of the proximity between the Lac X-spin and the Thr M-spin resonances, which are separated by ϳ0.15 ppm, Thr will be coedited in spectral editing for Lac. Because of the low signal intensity of Lac and Thr, and the similarity of their resonances and coupling characteristics, distinct quantification of Lac and Thr in human brain in vivo by 1 H MRS has not previously been addressed. Thr may be altered by dietary intake, such as when an infant is fed bovine formula (11) or in cases of protein deficiency (12), but the main intent in separating Thr and Lac is to improve the quantification of Lac, which may be important in metabolic disorders (13) and following brain insults (14).Here we report 1 H MRS discrimination between the A-spin resonances of Lac and Thr in human brain in vivo by means of J-difference editing. Three types of highly selective editing 180°RF pulses, implemented within an adiabatic-refocused double-echo localization sequence, were employed to generate three subspectra, from which both Lac and Thr difference spectra were extracted without lipid contamination. The optimum echo time (TE) was obtained by numerical analysis of the editing performance. Preliminary results indicate that Thr is present at a slightly higher concentration than Lac in the human occipital cortex. Figure 1a presents calculated spectra of Lac and Thr, at equal concentrations, following a single RF excitation pulse. The A-spin resonances of Lac and Thr overlap at 1.31 ppm. The Thr X-spin resonance at 3.58 ppm is not suitable for in vivo discrimination between the metabolites because of its overlap with the predominant multiplet of myo-inositol. The resonances of the Lac X-spin and the Thr M-spin differ by 0.15 ppm, and appear as a quartet and a doublet of quartet, respectively,...

Repeatability of edited lactate and other metabolites in astrocytoma at 3T

“…There may also be other coupled species that coedit with lactate, in particular threonine (37). It seems reasonable, however, to assume that the vast majority of the signal in tumors is due to lactate rather than threonine, since glycolytic overdrive has long been recognized as a common feature of tumors (38); however, some contribution of threonine to the edited peak in vivo cannot be excluded.…”

Challenges of Using MR Spectroscopy to Detect Neural Progenitor Cells In Vivo

“…Thus, spectral overlapping caused by J-coupling can be eliminated to provide spectra with better resolution. Spectral editing techniques can selectively suppress or emphasize certain resonances, and they have been widely used to detect overlapping or hidden signals, such as gamma-aminobutyric acid (GABA),39 glutamine/glutamate,40 and lactate (Lac) 41…”

Editing through multiple bonds: Threonine detection

“…Variants of the same technique were used to detect threonine in vivo in rat (6) and human (7) brains. Recently, a new J ‐difference editing method was used to quantify the threonine concentration in the human brain by discriminating between the lactate and threonine resonance at 1.32 ppm based on selective refocusing of the J ‐coupled partner at 4.11 ppm and 4.24 ppm (8). The results indicated that threonine (0.56 ± 0.06 mM) was present at slightly higher concentration than lactate (0.47 ± 0.07 mM) in the human occipital cortex (8).…”