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.

Multidimensional Proton Nuclear Magnetic Resonance Relaxation Morphological and Chemical Spectrum Graphics for Monitoring and Characterization of Polyunsaturated Fatty‐Acid Oxidation

“…At this autoxidation phase, polymerization/oligomerization products are known to be formed (Choe and Min, ). It is well reported that when analyzing large molecules such as polymers and or oligomers in a magnetic field, the T 1 relaxation time is stable and/or increases and T 2 declines (Bloembergen et al, ). This pattern is seen in the case of rapeseed oil and will be further discussed for PUFA oils.…”

Multifunctional particles: Magnetic nanocrystals and gold nanorods coated with fluorescent dye-doped silica shells

“…Figure 7 shows $R_2=T_2^{­1}$ plotted as a function of dispersed Fe concentration for the FePt@SiO 2 (Rubpy) and Fe 2 O 3 @SiO 2 (Rubpy) nanoparticles. The T 2 relaxivity, r 2 , indicates how strongly the paramagnet influences the proton spin relaxation of the surrounding water and is determined from the concentration dependence of R 2 [66,67,69]:…”

Effect of Gd‐DTPA‐BMA on blood and myocardial T1 at 1.5T and 3T in humans

“…The average difference in precontrast T 1 between 1.5T and 3T was larger for myocardium (0.16 ± 0.06 sec) than blood (0.08 ± 0.13 sec). The fact that myocardium T 1 increased more than blood from 1.5T to 3T may be attributed to the greater free water content and shorter molecular correlation times in blood (36), which would cause less field dependence on T 1 , in much the same way that water and CSF T 1 appear almost insensitive to field change. The trend toward similar blood and myocardium T 1 values at high field strength may lower image contrast between blood and myocardium on T 1 ‐weighted images.…”