Generating a gradient echo. This diagram show how the reversal of a magnetic field gradient is used to generate a gradient echo. The application of the 1st positive magnetic field gradient causes rapid de-phasing of the transverse magnetisation, Mxy, and therefore the FID signal to zero amplitude. The application of the 2nd negative magnetic field gradient reverses the de-phasing caused by the first gradient pulse, resulting in recovery of the FID signal to generate a gradient echo at the echo time, TE. Extension of the time duration of the second gradient to twice that of the first gradient causes the FID to then de-phase to zero. The maximum amplitude of the echo depends on both the T2* relaxation rate and the chosen TE.