Magnetic resonance relaxation

Magnetic resonance relaxation refers to microscopic physical mechanisms by which excited nuclear spins return to equilibrium after radiofrequency perturbation in the presence of an external magnetic field. The two most common types are spin-lattice relaxation (T₁), where energy from spins is transferred to their surroundings (the "lattice"), and spin-spin relaxation (T₂), where local interactions cause loss of coherence among spins, leading to signal decay. These processes, driven by dipole-dipole interactions, chemical shift anisotropy, and molecular motion, define how rapidly magnetization returns to equilibrium and how quickly the signal decays, respectively. Relaxation times (T₁, T₂) form the basis for tissue contrast and quantitative mapping in MRI, but are not themselves molecular targets; they report indirect information about molecular and cellular environments in vivo.

Other names

NMR relaxationMRI relaxationnuclear spin relaxationT₁ relaxation (spin-lattice relaxation)T₂ relaxation (spin-spin relaxation)longitudinal relaxationtransverse relaxation