Bloch simulation of a sample of isochromats, viewed in the rotating frame. B0 is along z.
16 TRs of 30° RF → stepped Gy phase-encode → Gx readout (gradient echo) → Gy rewinder → Gz spoiler. The signal is acquired only during the readout windows, shaded in the trace. Raise the speed to play it out faster.
The sample spans ±1 cm on each axis; a gradient of G Hz/cm shifts a spin at position x by G·x Hz.
Defaults are soft-tissue-like; try T2 ≈ 2000 ms (water/CSF) to keep Mxy around longer.
Try: apply a 90° pulse and watch the spins precess at Δf₀ while T2 slowly attenuates them and Mz recovers (T1). Turn up Gx and the spins fan out (dephase); a 180° pulse refocuses them into a spin echo.