Fine structure in the proton magnetic resonance spectrum of solid benzene and solid benzene-cyclohexane mixtures

The PMR spectrum of solid benzene in the vicinity of the melting point consists of broad and narrow lines. New narrow lines in the spectrum of benzene containing some impurity appear at the top of the broad line. Intensities of narrow lines increase with rising of temperature. The temperature dependence of line width and relaxation timesT ₁ andT ₂ have been measured in pure solid benzene an benzene-cyclohexane mixtures. It is assumed that narrow lines in spectra of pure benzene and its mixtures are caused by appearance of a phase with mobile molecules located in the crystallite joint or on its surface. The spectrum of imperfect monocrystalline benzene have been studied also. The narrow line of this sample is split into several narrow components. This is explained by demagnetization fields the distribution of which has a discrete character,     

A proton magnetic resonance investigation of some weak interactions in solution

The proton chemical shifts of cyclohexane, methyl iodide and iodoform are measured in a number of solvents. A complete calculation of the contribution to the solute proton chemical shift arising from the magnetic anisotropy of cylindrically symmetric solvents is given. Although the formula predicts the direction of the observed shifts, the observed values for non-polar solutes are always much larger than the calculated values. Some possible reasons for this are given and discussed.

The variation of the proton chemical shifts of the polar solutes methyl iodide and iodoform in aliphatic solvents are shown to agree with present theories of these effects. However, in aromatic solvents considerable deviations from the theoretical line are found and these are postulated to arise from solute solvent complexes in which the dipole axis of the solute lies along the hexagonal axis of symmetry of the benzene ring with the protons towards the ring. From the variation of the proton chemical shifts of methyl iodide and iodoform in toluene solution with temperature the following parameters were obtained. For the methyl iodide toluene complex the energy and entropy of formation are 1·3 ± 0·5 kcals/mole and 4·9 ± 0·4 e.u. respectively. For the iodoform toluene complex the corresponding values are 1·6 ± 0·2 kcals/mole and 6·4 ± 0·2 e.u.     

The proton magnetic resonance spectrum and the barrier to internal rotation for benzeneselenol in solution

The analysis of the proton magnetic resonance spectrum of a 5 mole% solution of benzeneselenol in CCl₄ at 305K yields ?0.45 Hz for the spin-spin coupling over six bonds between the sidechain proton and the ring proton in the para position. Comparison with the analogous couplings in phenol and in benzenethiol suggests that it is transmitted via a σ-π mechanism. Solution of the hindered rotor problem and allowance for error in measurement entails a two-fold barrier to internal rotation of 0.35 ± 0.25 kcal/mole for benzeneselenol. It would be of interest to compare this value to the as yet unknown barrier in the gas phase.     

High resolution proton magnetic resonance of selenophene

The high resolution proton magnetic resonance of selenophene has been studied at 100 Mc/s. The spectrum was analysed as an A₂X₂ system and the following coupling constants were obtained: J ₂₃ = 5·35, J ₂₄ = 1·05, J ₃₄ = 3·56, J ₂₅ = 2·47 c.p.s. Coupling was also observed between ⁷⁷Se and the α and β protons and coupling constants of 48 c.p.s. (α) and 9·5 c.p.s. (β) were obtained. The τ values were 2·30 (α) and 2·88 (β). The results are compared with values available for furan, pyrrole and thiophene and the conclusion is drawn that selenophene is probably a planar molecule.     

Evidence concerning the formation of a heterogeneous solid solution in the plastic phase of cyclohexane doped with a nitroxide free radical from magnetic resonance studies

Existing published E.P.R., nuclear spin lattice relaxation, dynamic nuclear polarization and electron-electron double-resonance data on the plastic phase of cyclohexane doped with a nitroxide free radical are re-examined and analysed in a consistent way. It is shown that (i) the local concentration of free radicals is higher than foreseen, assuming a uniform distribution and (ii) the molecular motions near the radical are slower than in the pure system. These results suggest that this system should be pictured as a heterogeneous solid solution where the local properties around the radicals are significantly different from those far from the radicals.     

Respiratory motion-corrected proton magnetic resonance spectroscopy of the liver

Purpose

To develop a post-processing, respiratory-motion correction algorithm for magnetic resonance spectroscopy (MRS) of the liver and to determine the incidence and impact of respiratory motion in liver MRS.

Materials and Methods

One hundred thirty-two subjects (27 healthy, 31 with nonalcoholic fatty liver disease and 74 HIV-infected with or without hepatitis C) were scanned with free breathing MRS at 1.5 T. Two spectral time series were acquired on an 8-ml single voxel using TR/TE=2500 ms/30 ms and (1) water suppression, 128 acquisitions, and (2) no water suppression, 8 acquisitions. Individual spectra were phased and frequency aligned to correct for intrahepatic motion. Next, water peaks more than 50% different from the median water peak area were identified and removed, and remaining spectra averaged to correct for presumed extrahepatic motion. Total CH₂+CH₃ lipids to unsuppressed water ratios were compared before and after corrections.

Results

Intrahepatic-motion correction increased the signal to noise ratio (S/N) in all cases (median=11-fold). Presumed extrahepatic motion was present in 41% (54/132) of the subjects. Its correction altered the lipids/water magnitude (magnitude change: median=2.6%, maximum=290%, and was >5% in 25% of these subjects). The incidence and effect of respiratory motion on lipids/water magnitude were similar among the three groups.

Conclusion

Respiratory-motion correction of free breathing liver MRS greatly increased the S/N and, in a significant number of subjects, changed the lipids/water ratios, relevant for monitoring subjects.     

Low temperature behaviour of proton magnetic resonance in metallocenes

Proton magnetic resonance of polycrystalline nickelocene and chromocene has been observed at temperatures between 20 and 1.6 K. It confirms that these metallocenes have temperature-independent paramagnetism in this temperature region. The origin of the observed line shape and position characteristic at low temperature is discussed.     

Current-induced magnetic resonance phase imaging

Electric current-induced phase alternations have been imaged by fast magnetic resonance image (MRI) technology. We measured the magnetic resonance phase images induced by pulsed current stimulation from a phantom and detected its sensitivity. The pulsed current-induced phase image demonstrated the feasibility to detect phase changes of the proton magnetic resonance signal that could mimic neuronal firing. At the present experimental setting, a magnetic field strength change of 1.7 +/- 0.3 nT can be detected. We also calculated the averaged value of the magnetic flux density BT parallel to B0 produced by electric current I inside the voxel as a function of the wire position. The results of the calculation were consistent with our observation that for the same experimental setting the current-induced phase change could vary with location of the wire inside the voxel. We discuss our findings in terms of possible direct MRI detection of neuronal activity.     

Decomposition of a solid solution in the ω phase of the Ti-Zr system under high pressure

Phase separation in the hexagonal ω modification of the Ti-Zr system was observed. The ω → ω₁ + ω₂ decomposition in an equiatomic TiZr alloy after prolonged thermal treatment at P = 5.5 ± 0.6 GPa and T = 440 ± 30°C was revealed using x-ray diffraction. It is found that the concentration dependence of the specific volume of the ω phase of Ti-Zr alloys deviates from the Vegard law to higher values. An isobaric section of the equilibrium P-T-x phase diagram of the Ti-Zr system is shown to have the shape of an eutectoid diagram at pressures higher than 8 GPa.     

Ring currents and proton magnetic resonance in aromatic molecules

The molecular orbital theory is adapted to the calculation of magnetic shielding constants in aromatic molecules. The usual lcao perturbation theory is generalized to take account of the imaginary perturbation due to an external magnetic field. The induced field at a point is then calculated by inserting a test dipole, adopting approximations due to London, and using the perturbation theory to evaluate a coupling energy. The results differ somewhat from those obtained in a rather different manner by Pople.     

Stray-field magnetic resonance imaging of solid materials

NMR imaging has experienced a tremendous increase in its use in a diverse range of investigations, particularly in the field of medical diagnostics. With regard to NMR imaging of solid materials, a number of challenges must be overcome before solid-state NMR imaging can experience widespread use. To date, a variety of strategies has been proposed for obtaining solid-state NMR images. In this paper, we will review the literature dealing with a specific solid-state NMR imaging method, stray-field imaging. We will describe our implementation of a two-dimensional version of the stray-field imaging method on a commercial instrument capable of collecting wideline NMR data and the use of this method in the examination of solid materials of interest in the aerospace industry.     

Bilateral filtering of magnetic resonance phase images

High-pass filtering is required for the removal of background field inhomogeneities in magnetic resonance phase images. This high-pass filtering smooths across boundaries between areas with large differences in phase. The most prominent boundary is the surface of the brain where areas with large phase values inside the brain are located close to areas outside the brain where the phase is, on average, zero. Cortical areas, which are of great interest in brain MRI, are therefore often degraded by high-pass filtering. Here, we propose the use of the bilateral filter for the high-pass filtering step. The bilateral filter is essentially a Gaussian filter that stops smoothing at boundaries. We show that the bilateral filter improves image quality at the brain's surface, without sacrificing contrast within the brain.     

Brain abscess observed by localized proton magnetic resonance spectroscopy

We encountered a case of brain abscess that was difficult to differentiate from glioblastoma. Localized ¹H-MRS was found to be useful for obtaining information on the biochemical status of brain abscess. The peak of lipid and high residual peak of NAA (N-acetyl-aspartate) were observed in the cystic lesion of the brain abscess by ¹H-MRS. The NAA/Cho (Choline-containing compounds) ratio in brain parenchyma showing an edematous lesion before therapy gradually increased with the relief of inflammation.     

含时磁共振系统的精确解和绝热近似解

在瞬时本征态完备基矢下,把一个经典含时磁共振系统的薛定谔方程转化为二阶常系数微分方程,实现了该量子系统的精确求解.利用该系统的精确解,讨论了绝热近似的精确程度,非常清晰地刻画了绝热近似解和精确解在量子态分布概率上的差异.结果表明,若系统初态制备于某个瞬时本征态上,系统保持在该瞬时本征态的概率介于0.888 9～1之间,...     

In vivo proton magnetic resonance spectroscopy studies of human brain

In vivo localized proton magnetic resonance spectroscopy (MRS) studies of brain were performed on eighteen normal subjects using the stimulated echo (STE) sequence. The absolute concentrations and proton relaxation times of N-acetyl aspartate (NAA), total creatine (Cr) and choline (Cho) were estimated. The MRS data was quantitatively analyzed for repeatability and intersubject variability. Quantitative analysis indicates excellent spectral repeatability. Significant intersubject variations in [NAA] and [Cr] have been observed while the intersubject variability in [Cho] has been found to be fairly small. Significant intensity distortions have been observed for mixing times longer than 50 msec.     

Superionic phase transition in disordered sublattice on the ferroelectric solid solution

The spontaneous formation of the dipole defects as the evidence of its coperative behaviour in paraelectric crystal is discussed.