What is a free induction decay (FID)?

FID: Free Induction Decay. An NMR Signal in the absence of any magnetic gradients.

An FID decays exponentially; at t = T2, 63.2% of the signal has been lost.

The decay curve is the signal envelope. The actual signal is oscillating at the resonance frequency in the MHz range.

3 MR PARAMETERS: SD, T1, T2, T2*