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

Abstract

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...

Hadamard-encoded localized high-resolution NMR spectroscopy via intermolecular double-quantum coherences

“…On the other hand, the methods, e.g. the dynamic nuclear polarization technique [31,32], focusing on improving the sensitivity of NMR experiments may be helpful in promoting the application of HL-IDEAL.…”

“…It has been adopted to localize the iDQC signal on a 3 T whole-body scanner [32]. In this study, the PRESS localization module was adapted to be comprised of three 180 • selective pulses in unison with slice selection gradient and flanked by a pair of spoiling gradients.…”

High-resolution 2D NMR spectra in inhomogeneous fields based on intermolecular multiple-quantum coherences with efficient acquisition schemes

“…It is a trade-off for the improvement of spectral resolution under inhomogeneous fields. Also, it has been demonstrated that the sensitivity of high-resolution iMQC spectroscopy is hardly affected by the inhomogeneity under small to moderate inhomogeneous fields (inhomogeneity <1.2 ppm) [16,36]. Several techniques such as dynamic nuclear polarization technique [10,37] have been utilized for iMQC signal intensity improvement.…”

Remote detection of hyperpolarized 129Xe resonances via multiple distant dipolar field interactions with 1H

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