Solvent suppression in liquid state NMR with selective intermolecular zero-quantum coherences

Magnetic resonance spectroscopy (MRS) techniques that use the distant dipolar field (DDF) to locally refocus inhomogeneous line-broadening promise improved spectral resolution in spatially varying fields. We investigated three possible implementations of localized DDF spectroscopy. Theoretical analysis and phantom experiments at 17.6 T showed that only localization immediately prior to acquisition provides sufficient spatial selectivity and sensitivity for in vivo applications. Spectra from an (8 mm) 3 voxel of the rat brain were acquired in 25 min, and three major metabolites were resolved. In a tumor mouse model, DDF spectra with well-resolved lines can be obtained from significantly larger voxels compared to conventional localized spectroscopy. From an inhomogeneous voxel, improved spectral resolution can be obtained with DDF techniques when a sufficient number of increments are sampled along the second spectral dimension. With fewer increments, measurement time is significantly shortened, and DDF techniques can provide higher signal-to-noise ratio ( Key words: iZQC; HOMOGENIZED; localized spectroscopy; inhomogeneous broadening; resolution enhancementIn vivo magnetic resonance spectroscopy (MRS) can be used to resolve spectral patterns to analyze the biochemical composition of tissue. High spectral resolution can be achieved when the magnetic field is extremely homogeneous over the region studied. Such field homogeneity is usually achieved with localized shimming procedures (1,2). If the region of interest (ROI) is strongly structured or includes air/tissue boundaries, homogeneous magnetic fields cannot be obtained and spectral resolution is often poor. One way to avoid inhomogeneous line-broadening caused by small-scale field variations is to use experimental techniques that exploit the effect of the distant dipolar field (DDF) originating from the sample magnetization (3-6). The homogeneity enhancement by intermolecular zeroquantum echo detection (HOMOGENIZED) experiment has been shown to produce narrow line shapes even under temporarily unstable magnetic fields (7), linear inhomogeneities across the sample volume (3-5), and field distortions in living organisms (8,9). Efficient water suppression (WS) and localization of the acquired signal are essential for in vivo applications. While different combinations of WS modules have been described and compared (5,10), the inherently low sensitivity of these methods has hampered the development of localization techniques in vivo (11).In this study we investigate three possible ways to combine localization with the HOMOGENIZED experiment, and demonstrate that high-quality spectra can be obtained in vivo. THEORY Theory of the HOMOGENIZED ExperimentThe HOMOGENIZED pulse sequence is a 2D NMR experiment derived from correlation spectroscopy (COSY) (3,12):The values in brackets indicate the flip angle of RF pulses with pulse phase given in subscript; t 1 is the incremented delay, CG is the correlation magnetic field gradient, and t 2 the acquisition period. The acquire...

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“…Signal from the selected volume is observed exclusively at f 1 ϭ ⌬ I -⌬ S (10). Therefore, the second term in Eq.…”

Section: Appendixmentioning

confidence: 99%

“…Efficient water suppression (WS) and localization of the acquired signal are essential for in vivo applications. While different combinations of WS modules have been described and compared (5,10), the inherently low sensitivity of these methods has hampered the development of localization techniques in vivo (11).…”

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confidence: 99%

Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Balla

Melkus

Faber

2006

Magnetic Resonance in Med

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“…Therefore, metabolite streaks were rotated counterclockwise by 63. 4 and then accumulatively projected onto the F2 axis to generate high-resolution 1D spectra. To maintain consistency for easy comparison, the data acquired with standard PRESS sequence were also processed using the same software.…”

Section: Methodsmentioning

confidence: 99%

“…As indicated in the ''Theory'' section, all metabolite peak streaks in the 2D spectra extended along the direction of 63. 4 relative to the F1 axis. Therefore, metabolite streaks were rotated counterclockwise by 63.…”

Section: Methodsmentioning

confidence: 99%

“…In the inhomogeneous fields, due to the broadening of spectral peaks along both F1 and F2 dimension, all the peaks appear as separate streaks along the direction / ¼ arctg (2) ¼ 63. 4 , where / is the angle of spectral streaks with respect to the F1 axis. Although the ranges of the streaks in both F1 and F2 dimensions are susceptible to inhomogeneity, an accumulated projection of the cross-peaks onto the F2 dimension after counterclockwise rotating the streaks by / results in a 1D high-resolution MRS without inhomogeneous broadening.…”

Section: Theorymentioning

confidence: 99%

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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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A New Method for High‐Resolution NMR Spectra in Inhomogeneous Fields with Efficient Solvent Suppression

Lin

Chen

et al. 2007

Chin. J. Chem.

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High-resolution nuclear magnetic resonance (NMR) is one of the most powerful tools for analyzing molecular structures and dynamics. Magnetic field homogeneity is required for conventional high-resolution spectra. However, there are many chemical and/or biological circumstances where the spatial homogeneities of the magnetic fields are degraded. Intense solvent signal is another obstacle for obtaining high-resolution spectra, especially in in vivo and in situ NMR spectroscopy. In this paper, a new pulse sequence based on intermolecular multiple quantum coherence (iMQC) was reported. This sequence can effectively remove the effect of magnetic field inhomogeneity and suppress the solvent signal. It can recover the spectral information such as chemical shifts, coupling constants, multiplet patterns, and relative peak areas in inhomogeneous fields. Theoretical analyses and experimental verifications are presented to demonstrate the feasibility of this method.

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Solvent suppression in liquid state NMR with selective intermolecular zero-quantum coherences

Cited by 44 publications

References 13 publications

Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

Spatially localized intermolecular zero‐quantum coherence spectroscopy for in vivo applications

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

A New Method for High‐Resolution NMR Spectra in Inhomogeneous Fields with Efficient Solvent Suppression

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