Investigation of Viscosity and Density Versus Temperature in Comparison with 1H Nmr Relaxation time Results for O,M-, P-Xylenes and α -,β-, γ - Picolines

The paper presents the results of density and viscosity measurements in liquid derivatives of benzene and pyridine, well purified, degassed or aerated, depending on temperature, in the whole liquidity range. Gaseous admixtures were found to affect the viscosity of liquids. From one to three Arrhenius regions were observed, depending on the structure and orientational freedom of the molecules. the results are discussed on the background of 1H NMR relaxation time studies with regard to the effect of dipole interactions on the structure of close packing.     

MR detection of mechanical vibrations using a radiofrequency field gradient

A new method for NMR characterization of mechanical waves, based upon radiofrequency field gradient for motion encoding, is proposed. A binomial B1 gradient excitation scheme was used to visualize the mobile spins undergoing a periodic transverse mechanical excitation. A simple model was designed to simulate the NMR signal as a function of the wave frequency excitation and the periodicity of the NMR pulse sequence. The preliminary results were obtained on a gel phantom at low vibration frequencies (0-200 Hz) by using a ladder-shaped coil generating a nearly constant RF field gradient along a specific known direction. For very small displacements and/or B1 gradients, the NMR signal measured on a gel phantom was proportional to the vibration amplitude and the pulse sequence was shown to be selective with respect to the vibration frequency. A good estimation of the direction of vibrations was obtained by varying the angle between the motion direction and the B1 gradient. The method and its use in parallel to more conventional MR elastography techniques are discussed. The presented approach might be of interest for noninvasive investigation of elastic properties of soft tissues and other materials.     

Detection of acoustic waves by NMR using a radiofrequency field gradient

A B(1) field gradient-based method previously described for the detection of mechanical vibrations has been applied to detect oscillatory motions in condensed matter originated from acoustic waves. A ladder-shaped coil generating a quasi-constant RF-field gradient was associated with a motion-encoding NMR sequence consisting in a repetitive binomial 13;31; RF pulse train (stroboscopic acquisition). The NMR response of a gel phantom subject to acoustic wave excitation in the 20-200 Hz range was investigated. Results showed a linear relationship between the NMR signal and the wave amplitude and a spectroscopic selectivity of the NMR sequence with respect to the input acoustic frequency. Spin displacements as short as a few tens of nanometers were able to be detected with this method.     

Body Temperature Mapping by Magnetic Resonance Imaging

Abstract

There are numerous clinical situations, such as hyperthermia cancer therapy, under which body temperature has to be accurately evaluated. Magnetic Resonance Imaging presently offers the best set of non-invasive methods for body temperature mapping, including diffusion imaging, relaxation time measurement, magnetization transfer contrast and chemical shift spectroscopic imaging. The basic NMR parameters involved in each are first analyzed. The role of temperature in their physical variation is then presented and finally the different practical MRI methods are briefly discussed. In the present slate of available technology and for basic physical reasons, the T 1 method appears the best compromise at low and medium magnetic field in a limited temperature range. Chemical shift could be theoretically more promising but strictly depends from the homogeneity and stability of the magnet and will be available only at high or very high field.

     

Non-Invasive Thermometry in Hyperthermia by NMR Chemical Shift

Summary

The temperature dependence of the chemical shift for protons of CH2 groups franked to D2O was supported experimentally. The linear correlation between these parameters was established for all animal tissues examined in vivo.

The temperature coefficient of regression common for all the tissues: as found as a value of (0.01010±0.0042) ppm/°C. On the basis of these data it seems most interesting to use the changes of the chemical shift for protons of GH2 groups relative to D2O as a standard for detection and mapping of the spatial temperature distribution inside of biological systems.

This method may be found useful for hyperthermia and thermodiagnosis.     

Determination of Radiation Dose Distribution by Magnetic Resonance Imaging in the New Tissue Equivalent Gel

Abstract

A new tissue-equivalent substance for the MR dosimetry has been developed. It is composed of water, bovine serum albumin, acrylamide with N,N′-methylene-bis-acrylamide, ammonium ferrous sulphate and sulphuric acid. The elemental composition, mass density, and electron density of the PIRA gel are closer to real tissue than those of dosimeter gels previously investigated. Irradiation causes the changes in the NMR properties of the gel. The dose dependence of NMR longitudinal relaxation rate, R1, is reproducible (less than 2% variation) and is linear up to about 30 Gy, with a slope of 0.023 s^?1Gy^?1 at 0.48 T. The gel, referred to as PIRA, can be used to obtain accurate radiation dose distribution with conventional magnetic resonance imaging devices.     

Selected States Magnetic Resonance Spectroscopy (SSMRS): Detection of Paramagnetic Element Dynamics

Abstract

Magnetic resonance (MR) response obtained in a strongly heterogeneous magnetic field with a linear gradient is analysed. It is shown that the employment of strong magnetic field gradients enables the MR spectroscopy to be accomplished in a system with selectively populated energy states (SSMRS). The method can be applied for measuring such physical quantities as the spin diffusion coefficient, D, spin-lattice, T_1m and spin-spin, T_2m, relaxation times and mobility, p_m, of paramagnetic elements in individual Zeeman energy states.

     

Temperature Dependence of the Depth of 1H NMR Absorption Line Splitting as an Engine Oil Quality Indicator Slope of the 1H NMR Absorption Line Splitting Depth,Lubricating Oils

The results of the investigations of oil quality level and wear ageing obtained by measuring the slope of the ¹H NMR absorption line splitting depth as a function of temperature for groups CH2 and CH3 have been reported.     

Electrical Mobility Magnetic Resonance Spectroscopy (EMMRS)

A method to determine electrical mobility of charge carriers containing paramagnetic elements is presented. The motion-induced phase shift of the transverse magnetization component is observed by magnetic (nuclear or electron) resonance (MR). In fluid media, this method can determine the type of carriers and respective motion, lifetimes distribution, thermal and frequency dispersion of the mobility, translational relaxation rate and activation energies of these processes.

     

A theoretical approach to local attenuation measurements of shear waves by MRE. Preliminary experimental results

An essential highlight of the presented method is the employment of Magnetic Resonance Elastography (MRE) for local measurements of the attenuation of elastic shear waves introduced into a biological sample. Such a measurement can be accomplished by combining the MRE method with those methods, in which collective displacement of spins is induced by external physical factors, such as variable electric field, strong magnetic field gradient or longitudinal elastic wave. A theoretical basis of the method involving external factors and results of preliminary experiments have been presented in this paper.