Basic Spin Properties and the Bloch Equations

In reality, spins are not isolated; instead, they interact with each other and their environment. The interaction of the spins with their surroundings leads to important modifications in their behavior. The experimentally determined spin-lattice relaxation time, T1, characterizes how quickly the longitudinal magnetization can grow back to its maximum value along the magnetic field direction. In contrast, T2 and T ∗ 2 are experimentally determined characteristic times describing the vanishing rate of the transverse magnetization. The T2 decay of signal is time-dependent and cannot be recovered, whereas part of the time-independent T ∗ 2 effect can be reversed by spin echo experiments.