Brain γ‐aminobutyric acid measurement by proton double‐quantum filtering with selective <i>J</i> rewinding

Choi, Changho; Coupland, Nicholas J.; Hanstock, Christopher C.; Ogilvie, Catherine J.; Higgins, Andrea C. M.; Gheorghiu, D.; Allen, Peter S.

doi:10.1002/mrm.20563

Cited by 29 publications

(26 citation statements)

References 27 publications

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“…This is inevitable for selective excitation between the Lac X spin (4.10 ppm) and the Thr M spin (4.25 ppm). Its impact might be mitigated by frequency offset adjustments during interleaved acquisitions (20).…”

Section: Resultsmentioning

confidence: 99%

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

Choi¹,

Coupland²,

Kalra³

et al. 2006

Magnetic Resonance in Med

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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,...

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Section: Resultsmentioning

confidence: 99%

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

Choi¹,

Coupland²,

Kalra³

et al. 2006

Magnetic Resonance in Med

Self Cite

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“…Hardware and software advances have allowed efficient implementation of computationally intensive numerical density matrix simulations, where some experimental conditions can be mirrored exactly, including experimental RF pulse shapes and gradient coherence selections (22,24). Recently, numerical simulations were used to optimize a double-quantum filtering sequence for GABA detection (25). Optimal sequence timings and the influence of homocarnosine contamination on the GABA signal were calculated using realistic pulse shapes.…”

Section: Introductionmentioning

confidence: 99%

A detailed analysis of localized J‐difference GABA editing: theoretical and experimental study at 4 T

et al. 2007

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The problem of low signal-to-noise ratio for gamma-aminobutyric acid (GABA) in vivo is exacerbated by inefficient detection schemes and non-optimal experimental parameters. To analyze the mechanisms for GABA signal loss of a MEGA-PRESS J-difference sequence at 4 T, numerical simulations were performed ranging from ideal to realistic experimental implementation, including volume selection and experimental radio frequency (RF) pulse shapes with a macromolecular minimization scheme. The simulations were found to be in good agreement with phantom and in vivo data from human brain. The overall GABA signal intensity for the simulations with realistic conditions for the MEGA-PRESS difference spectrum was calculated to be almost half of the signal simulated under ideal conditions (~43% signal loss). In contrast, creatine was reduced significantly less then GABA (~19% signal loss). The 'four-compartment' distribution due to J-coupling in the PRESS-based localization was one of the most significant sources of GABA signal loss, in addition to imperfect RF profiles for volume selection and editing. An alternative strategy that reduces signal loss due to the four-compartment distribution is suggested. In summary, a detailed analysis of J-difference editing is provided with estimates of the relative amounts of GABA signal losses due to various mechanisms. The numerical simulations presented in this study should facilitate both implementation of the more efficient acquisition and quantification process of J-coupled systems.

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“…Conventional (intramolecular) double-quantum filters have been utilized for suppression of strong singlets and optimal detection of J-coupled resonance, such as c-aminobutyric acid (27,28) and glutathione (29,30). Since intramolecular double-quantum coherences originate from J-coupling interaction, non-J-coupled spins give no signal.…”

Section: Human Volunteer Resultsmentioning

confidence: 99%

High‐resolution MRS in the presence of field inhomogeneity via intermolecular double‐quantum coherences on a 3‐T whole‐body scanner

Lin

Chen

et al. 2010

Magnetic Resonance in Med

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Signals from intermolecular double-quantum coherences (iDQCs) have been shown to be insensitive to macroscopic field inhomogeneities and thus enable acquisition of highresolution MR spectroscopy in the presence of large inhomogeneous fields. In this paper, localized iDQC 1 H spectroscopy on a whole-body 3-T MR scanner is reported. Experiments with a brain metabolite phantom were performed to quantify characteristics of the iDQC signal under different conditions. The feasibility of in vivo iDQC high-resolution MR spectroscopy in the presence of large intrinsic and external field inhomogeneity (in the order of hundreds of hertz) was demonstrated in the whole cerebellum of normal volunteers in a scan time of about 6.5 min. Major metabolite peaks were well resolved in the reconstructed one-dimensional spectra projected from two-dimensional iDQC acquisitions. Investigations on metabolite ratios, signal-to-noise ratio, and line width were performed and compared with results obtained with conventional point-resolved spectroscopy/MR spectroscopy in homogeneous fields. Metabolite ratios from iDQC results showed excellent consistency under different in vitro and in vivo conditions, and they were similar to those from point-resolved spectroscopy with small voxel sizes in homogeneous fields. MR spectroscopy with iDQCs can be applied potentially for quantification of gross metabolite changes due to diseases in large brain volumes with high field inhomogeneity. Magn Reson Med 63:303-311, 2010. V C 2010 Wiley-Liss, Inc.Key words: intermolecular double-quantum coherences (iDQCs); inhomogeneous broadening; high-resolution; localized spectroscopy; human cerebellumIn vivo magnetic resonance spectroscopy (MRS) allows noninvasive analysis of metabolites in humans. It is widely used for investigation of pathogenesis, monitoring metabolite responses, and clinical diagnosis of cancers and various neurologic diseases. However, magnetic field homogeneity in vivo is often degraded by magnetic susceptibility variation near, for example, air/tissue interfaces, bones and cerebrospinal fluid in brain, or with large interferences from fat and other fluid signals in the prostate. The field distortions can be as large as 2.0 part per million (ppm) over a 20 Â 20 Â 20 mm 3 voxel (1) and are not well corrected with the 1st-and 2nd-order shimming available in most clinical MR scanners. Under such circumstances, spectra obtained by conventional MRS techniques are often poor and unusable. One way to remove the effect of inhomogeneous fields up to hundreds of hertz is to use techniques based on intermolecular multiple-quantum coherences that originate from dipole-dipole interactions between spins of different molecules. Intermolecular zero-quantum coherences (iZQCs) have been explored to obtain high-resolution spectra from nonlocalized controlled inhomogeneous samples (2-4) and biologic samples (5-7) at high magnetic fields. Localized iZQC spectra of living animals were also obtained on a 17.6-T spectrometer (8,9). In comparison to the iZQCs, previous...

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Brain γ‐aminobutyric acid measurement by proton double‐quantum filtering with selective J rewinding

Cited by 29 publications

References 27 publications

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

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

A detailed analysis of localized J‐difference GABA editing: theoretical and experimental study at 4 T

High‐resolution MRS in the presence of field inhomogeneity via intermolecular double‐quantum coherences on a 3‐T whole‐body scanner

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