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.     

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.     

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.     

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.     

Cardiac self-gating using blind source separation for 2D cine cardiovascular magnetic resonance imaging

PurposeTo develop and validate a new cardiac self-gating algorithm using blind source separation for 2D cine steady-state free precession (SSFP) imaging.MethodsA standard cine SSFP sequence was modified so that the center point of k-space was sampled with each excitation. The center points of k-space were processed by 4 blind source separation methods, and used to detect heartbeats and assign k-space data to appropriate time points in the cardiac cycle. The proposed self-gating technique was prospectively validated in 8 patients against the standard electrocardiogram (ECG)-gating method by comparing the cardiac cycle lengths, image quality metrics, and ventricular volume measurements.ResultsThere was close agreement between the cardiac cycle length using the ECG- and self-gating methods (bias 0.0 bpm, 95% limits of agreement ±2.1 bpm). The image quality metrics were not significantly different between the ECG- and self-gated images. The ventricular volumes, stroke volumes, and mass measured from self-gated images were all comparable with those from ECG-gated images (all biases <5%).ConclusionThe self-gating method yielded comparable cardiac cycle length, image quality, and ventricular measurements compared with standard ECG-gated cine imaging. It may simplify patient preparation, be more robust when there is arrhythmia, and allow cardiac gating at higher field strengths.     

磁共振波谱与成像技术

文章简要介绍了核磁共振的基本原理,详细阐述了液体核磁共振在蛋白质结构、功能和动力学等方面的研究进展,论述了增强固体核磁共振分辨率的方法及其应用,讲述了磁共振成像的原理并综述了不同磁共振成像方法的应用研究进展,并对核磁共振的发展作了展望。     

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.     

Signal profile measurements of single- and double-volume acquisitions with image-selected in vivo spectroscopy for 31P magnetic resonance spectroscopy

The volume-selection performance was studied for single- and double-volume-of-interest (VOI) acquisition with the volume-selection method image-selected in vivo spectroscopy for ³¹P magnetic resonance spectroscopy. High-resolution signal profiles were measured using a phantom simulating a brain. Inside the phantom there was a small, remotely controlled, movable signal source filled with ortho-phosphoric acid. Signal profiles of the VOI were measured in three perpendicular directions for 1VOI (single VOI) and 2VOI (double VOI) acquisition. The measured signal profiles for both acquisitions were very similar, but they showed a discrepancy with regard to the intended VOI (iVOI). The transition regions were on average 3.8 mm and the average full width at half maximum of the signal profile was 30 mm for an iVOI size of 30130130 (mm³). No displacement was observed in the signal profiles. To avoid overlapping signal profiles, the minimum separation between two iVOIs was found to be 10 mm in our magnetic resonance (MR) system. A substantial negative signal contribution from regions outside the iVOI was measured in the y-direction for 1VOI acquisition and one of the two VOIs in 2VOI acquisition. The other VOI in 2VOI acquisition exhibited only minor contamination. The measurements presented underline the importance of detailed knowledge on the volume selection performance in in vivo magnetic resonance spectroscopy.     

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.