Relaxation Effects in Nuclear Magnetic Resonance Absorption

Abstract

The exchange of energy between a system of nuclear spins immersed in a strong magnetic field, and the heat reservoir consisting of the other degrees of freedom (the "lattice") of the substance containing the magnetic nuclei, serves to bring the spin system into equilibrium at a finite temperature. In this condition the system can absorb energy from an applied radiofrequency field. With the absorption of energy, however, the spin temperature tends to rise and the rate of absorption to decrease. Through this "saturation" effect, and in some cases by a more direct method, the spin-lattice relaxation time T 1 can be measured. The interaction among the magnetic nuclei, with which a characteristic time T 2 ' is associated, contributes to the width of the absorption line. Both interactions have been studied in a variety of substances, but with the emphasis on liquids containing hydrogen.Magnetic resonance absorption is observed by means of a radiofrequency bridge; the magnetic field at the sample is modulated at a low frequency. A detailed analysis of the method by which T 1 is derived from saturation experiments is given. Relaxation times observed range from 10-4 to 10 2 seconds. In liquids T 1 ordinarily decreases with increasing viscosity, in some cases reaching a minimum value after which it increases with further increase in viscosity. The line width meanwhile increases monotonically from an extremely small value toward a value determined by the spin-spin interaction in the rigid lattice.

Fast and optimized T1 mapping technique for the noninvasive quantification of gastric secretion

“…The influence of field strength can be ignored since all MRI measurements were performed at 1.5T. The results of a previous study (8) with theoretical models described in the literature (18,19). An increase in macromolecular content causes a reduction of the correlation times of the Gd-DOTA chelate or the water molecule, or both, leading to an increased rate of spin interaction.…”

Electron spin–lattice relaxation of nitroxyl radicals in temperature ranges that span glassy solutions to low-viscosity liquids

“…2,2,6,6-Tetramethylpiperidin-1-oxyl (tempo), 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (tempol), 4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl (tempone) (Aldrich Chemical Co.); 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl (CPROXYL), 3-carbamoyl-2,2,5,5-tetramethylpyrrolin-1-oxyl (CTPO) (Eastman Kodak Co.); 15 N-tempone, tempone-d 16 , tempol-d 17 , and 15 N-tempol-d 17 (CDN Isotope) were used as received. TPHIO was prepared as reported in ref.…”

“…However, there was ∼10% difference between derived τ values for tempol and tempol-d 17 in water:glycerol. The linewidths in the spectra of tempol are broader than for tempone and are substantially broader for tempol than for tempol-d 17 and 15 N-tempol-d 17 , which may introduce systematic errors in the calculation of τ. The average τ values obtained for tempol-d 17 and 15 N-tempol-d 17 were used in the analysis of the dependence of 1/T 1 on tumbling.…”

“…(8) The BPP function assumes that the reorientational motions are stochastic and that only one ensemble of reorienting units is present. The BPP correlation function is an exponential [17].…”

1H NMR study of internal motions and quantum rotational tunneling in (CH3)4NGeCl3

“…Albert et al [25] have assumed that the observed curves could be described by two superimposed BPP curves [31] and the effective relaxation rate is the sum of the relaxation rates due to the intramethyl and intermethyl contributions and hence can be written as…”