Longitudinal or spin-lattice relaxation time

The recovery of the Zeeman polarization to its equilibrium value is characterized by the longitudinal, or spin-lattice relaxation time constant Tiz. Spin-lattice relaxation occurs through dissipation of the excess energy of the spins to the surrounding lattice, brought about by fluctuating fields of the appropriate frequencies, i.e., close to the Larmor frequency cdq and to 2(Oq. 

In words, this says that the "-magnetization returns from Mz 0) to Mz following an exponential law. The time constant of the exponential is 1/RZ, and this is often called T], the longitudinal or spin-lattice relaxation time. 

Bearing in mind that the nuclear spin system is an ensranble perturbed by the rf-field, we have to consider the possibility that energy from the rf-field is transferred to the nuclear spins and dissipated further to the crystal lattice. These effects can be described by relaxation times that characterize the rates with which the system returns to thermal equilibrium after the perturbation has been switched off. There are the longitudinal or spin-lattice relaxation time Tj and the transverse or spin-spin relaxation time Tj. Including the relaxation effects the equations of motion in the rotating frame (cf. Eq. (19)) are... 

In NMR, Tj is called the longitudinal or spin-lattice relaxation time.14 it represents the rate at which energy is exchanged between the spin system and the surroundings. Since in microwave experiments, energy is stored in the form of a population difference, the connection between these interpretations is clear. T2 in NMR is called the transverse or spin-spin relaxation time.14 It represents the rate at which individual spins lose coherence. In the experiments discussed here, T2 can be interpreted as a loss of coherent polarization due to molecular interactions. 

DTPA = diethylenetriaminepentaacetic acid DOTA = l,4,7,10-tetraazacyclododecane-l,4,7,10-tetraacetic acid MRI = magnetic resonance imaging NMR = nuclear magnetic resonance T = longitudinal or spin lattice relaxation time Ti = transverse or spin-spin relaxation time r = longitudinal relaxivity V2 = transverse relaxivity. 

Boltzmann statistics, the difference in population of the Zeeman levels is therefore extremely small. The absorption of photons of energy h would rapidly equalize these populations (bringing the spin temperature to infinity) if no other process than Einstein s spontaneous emission would contribute to restore the equilibrium Boltzmann distribution. Indeed, the natural life time at these frequencies is of the order of 10 s, while in practice the equalization of the spin temperature with the lattice temperature requires time of the order of the second in liquids. The relaxation mechanisms which act in these circumstances are linked to the fluctuation of the magnetic field (or quadrupolar coupling) inside of the sample, more precisely to the Fourier component of this fluctuation at the NMR frequency. The relaxation so far described correspond to the recovery of the z component of the magnetisation which measures the actual difference of population of the Zeeman levels. Therefore it is called longitudinal or spin lattice relaxation time T. ... 

Tj is the longitudinal or spin-lattice relaxation time and T2 is the transverse or spin-spin relaxation time. 

The IR or SR pulse sequences give access to the longitudinal (or spin-lattice) relaxation time Tj of the different hydrogen components within... 

---