T2 or Transverse relaxation time

·         Also called spin-spin relaxation

·         A 90^O RF pulse causes phase coherence of the individual spinning protons and generates the maximum transverse magnetization (M_XY) for a given sample

·         As M_XY rotates at a given frequency  (Larmor frequency) – the receiver antenna is induced (by magnetic induction – changing magnetic field creating electronic current) to produce a sinusoidal electronic signal  - The FREE INDUCTION DECAY (FID) signal

·         FID decay is as a result of the loss of phase coherence of the individual spins

·         Inhomogeneities intrinsic to and extrinsic (from the magnet or ferromagnetic and paramagnetic materials – casue faster dephasing) to the sample structure cause a spin-spin interaction and the individual spins precess at different frequencies due to slight changes in the local magnetic field strength

·         The elapsed time between the peak M_XY and 37% of the peak is the T2* constant (when both intrinsic and extrinsic inhomogeneities are taken into account)

·         T2* mechanisms are determined by the molecular structure of the sample

	T2
General time	Short (5-10x)
Large; slowly vibrating; bound molecules	Short (++ intrinsic inhomogeneities)
Intermediatly sized, vibrating and bound molecules (Viscous materials – lipids/proteins/fats)	Short (also extrinxic inhomogeneities speed up dephasing)
Small; fast vibrating; free molecules	Long (decreased intrinsic inhomogeneities)
Influence of magnetic field strength (increase)	Insignificant
Paramagnetic blood degredation products; gadolinium; ferromagnetic materials	Shortened T*2 (Disruption of local magnetic field environment)