What term describes signal dephasing due to local inhomogeneities in MRI?

The term that describes signal dephasing due to local inhomogeneities in MRI is T2*. T2* is a measure of the decay of the transverse component of magnetization due to both spin-spin interactions and variations in the magnetic field, causing different spins to experience slightly different magnetic environments. This results in dephasing of the spins, which leads to a reduction in the signal observed in MRI imaging.

T1 refers to longitudinal relaxation time, which measures the time it takes for the longitudinal magnetization to return to its equilibrium state after excitation. While it is an important parameter in MRI, it does not specifically address signal dephasing from local variations in the magnetic field.

T2 represents the time constant that accounts for dephasing due to interactions between nearby spins in a uniform magnetic field, but it does not incorporate the additional effects from field inhomogeneities.

T3 is not a standard term used in MRI; thus, it does not apply in the context of signal dephasing or any relaxation processes measured in MRI.

Overall, T2* is specifically associated with the effects of local field inhomogeneities, differentiating it from the other terms related to MRI relaxation processes.