One simulated brain, imaged with different scanner timing. Move the sliders and watch which tissues turn bright or dark: white matter, grey matter and fluid (CSF).
PD-weighted
Spin echo · TR 10 s · TE 15 ms
The same noise is added in every mode. Fast gradient-echo scans get little signal per pulse, so real scans average many repeats to make up for it.
short (T1 matters more)long
shortlong (T2 matters more)
small (PD-weighted)large (T1-weighted)
Try
Brightest to darkest (≈ means within 5%)
Signal from each tissue (not rescaled; 100% = fully recovered pure water)