Localized intermolecular zero‐quantum coherence spectroscopy in vivo

Abstract

Resolution enhancement in NMR spectra, acquired in spatially or temporally varying magnetic fields, can be achieved with 2D pulse sequences detecting intermolecular zero-quantum coherences (iZQC). The insensitivity towards long range field distortions renders these methods particularly appealing for in vivo NMR spectroscopy, where ample sources of field inhomogeneities are encountered. This article provides a comprehensive description of iZQC spectroscopy, following a classical treatment. A pictorial explanation is given of how iZQC signal is formed under the action of the distant dipolar field in the sample and how this local refocusing process leads to line narrowing in the indirect dimension of 2D spectra. Signal evolution and peak positions in the spectra are analyzed by solving the modified Bloch equations. Finally, it is explained how water suppression and localization can be combined with the iZQC preparation sequence, and recent in vivo applications are discussed. The given examples illustrate that iZQC spectroscopy can provide either resolution or sensitivity enhancement in vivo

Spatially Localized Two-Dimensional J-Resolved NMR Spectroscopy via Intermolecular Double-Quantum Coherences for Biological Samples at 7 T

“…The J coupling information of the metabolites, such as the methyl group of low-density lipoprotein (LDL) at 0.93 ppm and lactate (Lac) at 1.34 ppm, can be extracted along the F1 dimension. Because of the prolate shapes and surrounding bone structures, the field shimming for the fish spinal cord region is generally challenging [ 36 ]. Thus, when the large voxel containing the fish spinal cord is selected, the quality of the resulting 2D J PRESS spectrum remarkably decreases even after field shimming ( Fig 4D ).…”

NMR Separation of Intra- and Extracellular Compounds Based on Intermolecular Coherences

“…In the SOLO NMR experiment, either the intra-or the extracellular water resonance was excited, and thus the refocusing DDF was created in only one of the two compartments. The reach of the DDF was confined to the intracellular volume by using sufficiently large correlation gradient amplitudes (18)(19)(20)31). Because X. laevis oocytes are large single cells with a size of~1 mm in diameter, gradient pulses were adjusted to a strength of 200 mT/m, resulting in a correlation distance of 0.1 mm.…”

“…The local reach of the action of the DDF is characterized by d c ¼ p/gGT, with g being the gyromagnetic ratio and G and T strength and duration of the experimentally applied gradient pulse to disturb the symmetry in the sample (18)(19)(20). This correlation gradient is the key factor for DDF NMR spectroscopy, in particular for solvent-localized (SOLO) NMR spectroscopy.…”

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

“…After a shearing process [11,15,16], a high-resolution 1D spectrum free of inhomogeneous broadenings can be extracted from the projection along one dimension of the acquired 2D spectrum while the information along the other dimension containing inhomogeneous broadenings are discarded. The high-resolution iMQC spectroscopy has been applied to the in vivo localized magnetic resonance spectroscopy (MRS) with field-distorted voxels, where the spectral linewidths are broadened by the magnetic field gradients caused by susceptibility differences between tissues, bones and air [17][18][19][20][21].…”