Ultrafast hetero-nuclear 2D J-resolved spectroscopy

Ultrafast techniques enable the acquisition of 2D NMR spectra in a single scan. In this study, we propose a new ultrafast experiment designed to record hetero-nuclear (1)H-(13)C J-resolved spectra in a fraction of a second. The approach is based on continuous constant-time phase modulated spatial encoding followed by a J-resolved detection scheme. An optional isotopic filter is implemented to remove the signal arising from (1)H bound to (12)C. While the most evident application of the technique proposed in this paper is the direct measurement of one bond scalar (13)C-(1)H couplings for structural elucidation purposes, it also offers interesting potentialities for measuring (13)C isotopic enrichments in metabolic samples. The main features of this methodology are presented, and the analytical performances of the ultrafast hetero-nuclear J-resolved pulse sequence are evaluated on model samples.     

A new detection scheme for ultrafast 2D J-resolved spectroscopy

Recent ultrafast techniques enable 2D NMR spectra to be obtained in a single scan. A modification of the detection scheme involved in this technique is proposed, permitting the achievement of 2D 1H J-resolved spectra in 500 ms. The detection gradient echoes are substituted by spin echoes to obtain spectra where the coupling constants are encoded along the direct nu2 domain. The use of this new J-resolved detection block after continuous phase-encoding excitation schemes is discussed in terms of resolution and sensitivity. J-resolved spectra obtained on cinnamic acid and 3-ethyl bromopropionate are presented, revealing the expected 2D J-patterns with coupling constants as small as 2 Hz.     

New developments in nuclear magnetic resonance using noise spectroscopy

In the 30 years since Ernst and Kaiser introduced the idea of incoherent radiation fields and their application to NMR spectroscopy, relatively few researchers have exploited the advantages of noise spectroscopy. Some recent applications of one-dimensional noise spectroscopy in NMR are presented which display a versatility which commonly is not appreciated. Excitation schemes are discussed which demonstrate both broadband and narrowband features, and demonstrate both theoretically and experimentally how noise spectroscopy allows for the observation of distortion-free broadline spectra in solids whichmay not be amenable to techniques more traditionally used in pulsed NMR experiments. It is argued that these applications of noise spectroscopy deserve a more common place in the experimentalists arsenal.     

Reproducibility of magnetic resonance imaging measurements of spinal cord atrophy: the role of quality assurance.

A sensitive magnetic resonance imaging (MRI) method to measure spinal cord cross-sectional area with the potential to monitor disease progression has recently been developed. As changes in cord area due to disease are usually small, assessment of the reliability of the methodology is essential in serial studies of spinal cord atrophy. The aim of this study was to institute and evaluate a protocol of quality assurance to determine long-term reproducibility of serial studies. Serial MRI of the spinal cord was carried out in five healthy volunteer controls over 1 year. Cross-sectional spinal cord areas were measured in a total of 46 scans. The mean coefficient of variation of all subjects over one year was 1.35%. The intra-observer coefficient of variation for same scan analysis was 0.63%. This study has confirmed high reliability of our serial data over one year and the on-going quality assurance protocol enables continuing evaluation of the reproducibility of results in serial studies. Quality assurance is an essential and practical component of all serial MRI studies, without which the clinical implications of change cannot be reliably evaluated.     

Porosity measurements in natural porous rocks using magnetic resonance imaging

A magnetic resonance imaging (MRI) method is presented to measure localized porosity values inside natural porous rocks for the purpose of obtaining frequency distributions of the porosity (porosity distributions). The method is applied to study six different cores, including three Berea sandstone samples, Casper sandstone, Indiana limestone, and San Andres dolomite. An image of the porosity is shown for a transverse and a longitudinal slice in order to show qualitative variations of the porosity within each core sample. The porosity distribution for the entire core has been acquired, and it is shown with a Gaussian fit to the data. In addition, for cores known to have a layered structure, a bimodal distribution is fit to the data, and the fit is used to estimate the value of the porosity for two characteristic types of layers within the core sample.     

Single-spin measurements for quantum computation using magnetic resonance force microscopy

The quantum theory of a single-spin measurement using magnetic resonance force microscopy is presented. We use an oscillating cantilever-driven adiabatic reversal technique. The frequency shift of the cantilever vibrations is estimated. We show that the frequency shift causes the formation of a Schrödinger cat state for the cantilever. The interaction between the cantilever and the environment quickly destroys the coherence between the two cantilever trajectories. It is shown that using partial adiabatic reversals one can obtain a significant increase in the frequency shift. We discuss the possibility of sub-magneton spin density detection in molecules using magnetic resonance force microscopy.     

Studies of ion-solvent and ion-ion interactions using nuclear magnetic resonance spectroscopy

Chemical shifts of the fluorine nuclear resonance have been measured for fluoride ion in a variety of environments. The shift varies linearly with the mole-fraction of organic solvent and is dependent upon the nature and concentration of added cations and anions. In contrast, the value for the caesium resonance from solutions of caesium salts is independent of the choice of solvent. Large, linear, chemical shifts are observed when other electrolytes are added, the effect being almost entirely due to the anions.     

Relaxation studies in magnetic resonance spectroscopy

The electron spin and nuclear spin relaxation in liquid solution arising from the electron-nuclear interaction is determined for the general case when the g-tensor may be anisotropic and the nine hyperfine interaction tensor components may be all different. The theoretical expressions are used in an attempt to interpret the relaxation times T ₁ and T ₂ for the various nuclei in the complex ruthenium acetylacetonate.     

Improving spectral resolution in spatial encoding dimension of single-scan nuclear magnetic resonance 2D spin echo correlated spectroscopy

The spatial encoding technique can be used to accelerate the acquisition of multi-dimensional nuclear magnetic resonance spectra. However, with this technique, we have to make trade-offs between the spectral width and the resolution in the spatial encoding dimension (F1 dimension), resulting in the difficulty of covering large spectral widths while preserving acceptable resolutions for spatial encoding spectra. In this study, a selective shifting method is proposed to overcome the aforementioned drawback. This method is capable of narrowing spectral widths and improving spectral resolutions in spatial encoding dimensions by selectively shifting certain peaks in spectra of the ultrafast version of spin echo correlated spectroscopy (UFSECSY). This method can also serve as a powerful tool to obtain high-resolution correlated spectra in inhomogeneous magnetic fields for its resistance to any inhomogeneity in the F1 dimension inherited from UFSECSY. Theoretical derivations and experiments have been carried out to demonstrate performances of the proposed method. Results show that the spectral width in spatial encoding dimension can be reduced by shortening distances between cross peaks and axial peaks with the proposed method and the expected resolution improvement can be achieved. Finally, the shifting-absent spectrum can be recovered readily by post-processing.     

Resolution and sensitivity aspects of ultrafast J-resolved 2D NMR spectra

Recent ultrafast techniques enable nD NMR spectra to be obtained in a single scan. However, resolution enhancement in the ultrafast domain leads to important sensitivity losses and lineshape distortions. In order to understand better resolution and spatial encoding aspects of continuous phase-encoding schemes, a theoretical and experimental comparison of different excitation patterns is carried out. Molecular diffusion appears to be the main cause of signal-to-noise ratio decrease, and a multi-echo excitation scheme is proposed to limit its effects when a good resolution is needed. Results obtained on 2D J-resolved spectra are presented.     

Simultaneous magnetic resonance gadolinium-enhanced 2D perfusion and 3D angiographic imaging

A method was implemented and tested that allows the simultaneous acquisition of magnetic resonance 2D slice selective perfusion and 3D angiographic data during a single bolus injection of a contrast agent. High quality contrast-enhanced perfusion images and angiograms of the lung, kidney and heart were obtained in healthy volunteers. Combined perfusion and angiography provided additional information with an acceptable increase in acquisition time. No image artifacts were attributed to the technique. The combined information may be useful in detecting, as well as characterizing, vascular abnormalities.     

A heteronuclear intermolecular single-quantum coherence scheme for high-resolution 2D J-resolved 1H NMR spectra in inhomogeneous magnetic fields

Based on heteronuclear intermolecular single-quantum coherences between proton (¹H) and quadrupolar nuclei (i.e. deuterium ²H), a three-dimensional nuclear magnetic resonance (NMR) pulse sequence is proposed for recovering high-resolution two-dimensional J-resolved NMR spectra from samples mixed with a deuterated solvent in the presence of large magnetic field inhomogeneities. Benefitting from excitation of spins via two different radio frequency (RF) transmit channels, this sequence is suitable for applications in randomly large inhomogeneous fields and the solvent suppression generally required in homonuclear intermolecular multiple-quantum coherence approaches is no longer necessary. Systematic theoretical analyses are given based on the distant dipolar field treatment. Experiment on a sample of corn oil in deuterated acetone and ethyl 3-bromopropionate and acetone dissolved in DMSO-d₆ in a deshimmed field with severe inhomogeneous broadening is performed to show the feasibility and applicability of this sequence.     

Double-resonance circuit for nuclear magnetic resonance spectroscopy

A new double-resonance probe circuit design is described. The circuit contains no quarter-wavelength elements or equivalents, yet nonetheless achieves adequate isolation between the two input channels. It contains relatively few components, and so is both compact and efficient. It has been incorporated in two solid-state nuclear magnetic resonance (NMR) probes, with excellent results.