Transverse relaxation time constant

The real power of MRI is the ability to exploit the inherent NMR properties of different tissues and tissue pathologies. The main MR parameters are known as longitudinal-relaxation time-constant (Tl), describing the time for the magnetization to recover to its equilibrium along the main-field axis after RF perturbation transverse-relaxation time-constant (T2), describing the... 

Equation (2.71) is used to describe the shapes of magnetic resraiance absorption lines in terms of the transverse relaxation time constant (Jf). We U use it similarly in Chaps. 4 and 10 to describe the shapes of optical absorption bands. 

K = 63 M 1, Kb = 1.4M-1)47 lithium-7 (K = 14 M 1 K" = 0.5 M 1) 49) and for cesium-133 (K, st 50 M-1, K = 4M 1)S0). In the case of sodium-23, transverse relaxation times could also be utilized to determine off-rate constants k ff = 3 x 105/sec k"ff = 2x 107/sec47,51). Therefore for sodium ion four of the five rate constants have been independently determined. What has not been obtained for sodium ion is the rate constant for the central barrier, kcb. By means of dielectric relaxation studies a rate constant considered to be for passage over the central barrier, i.e. for jumping between sites, has been determined for Tl+ to be approximately 4 x 106/sec 52). If we make the assumption that the binding process functions as a normalization of free energies, recognize that the contribution of the lipid to the central barrier is independent of the ion and note that the channel is quite uniform, then it is reasonable to utilize the value of 4x 106/sec for the sodium ion. 

Relaxation is an inherent property of all nuclear spins. There are two predominant types of relaxation processes in NMR of liquids. These relaxation processes are denoted by the longitudinal (Ti) and transverse (T2) relaxation time constants. When a sample is excited from its thermal equihbrium with an RF pulse, its tendency is to relax back to its Boltzmann distribution. The amount of time to re-equilibrate is typically on the order of seconds to minutes. T, and T2 relaxation processes operate simultaneously. The recovery of magnetization to the equilibrium state along the z-axis is longitudinal or the 7 relaxation time. The loss of coherence of the ensemble of excited spins (uniform distribution) in the x-, y-plane following the completion of a pulse is transverse or T2... 

The exchange of the coordinated aqua ligand of the W(IV) aqua oxo species was qualitatively studied by NMR line-broadening as a function of temperature based on Eq. (26), where the transverse relaxation time of the bound oxygen-17 nucleus is given by 1/T2b. The l/T2Qb represents the quadrupolar relaxation rate and kmi the chemical exchange rate constant... 

There is, in addition, another generally different time required to specify the radiofrequency behavior of the nuclear spin system. This time is called the transverse relaxation time and is the time constant for the exponential decay of the transverse (x and y) components of nuclear magnetization M- and M ... 

From the simpler resonance line-shape and H/D-exchange analysis to the more complex studies of inherent dynamics, occurring on various time scale of motion, NMR remains a good choice to investigate protein flexibility and plasticity. If linebroadening due to exchange and inhomogeneity is minimized (or completely eliminated), then half-width, Aom, of a line becomes proportional to R, the transverse relaxation rate constant. 

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