T2* (also called T2 Star) is composed of molecular interactions (spin spin relaxation) and local magnetic field non-uniformities. Caused by this the protons precess at slightly different frequencies. The T2* effect cause a rapid loss in coherence and transverse magnetization. The T2* time is less than the T2 time.

See also T2* Time, T2 Star.

The xy component of the net magnetization vector at right angles to the main magnetic field. The precession of the transverse magnetization at the Larmor frequency is responsible for the detectable MRI signal. In the absence of externally applied RF energy, the transverse magnetization will decay to zero with a characteristic time constant of T2, or more strictly T2*.