← MRI subtopic / Sim: TR / TE Explorer
TR / TE Explorer
Drag the sliders. Three tissues (fat, white matter, CSF) respond differently to the TR (repetition) and TE (echo) you choose — and that's the entire basis of contrast weighting.
500
15
Fat
—
White matter
—
CSF
—
Fat
Fat
WM
White matter
CSF
CSF
T1w (short TR, short TE)
PD (long TR, short TE)
T2w (long TR, long TE)
Start by dragging TR short (<600 ms) and TE short (<30 ms).
Fat should go bright, CSF should go dark — that's T1-weighting.
What you're seeing
The simulated signal is S = (1 − e−TR/T1) × e−TE/T2 — the spin-echo
signal equation ignoring proton density differences. T1 and T2 values used are typical 1.5 T numbers:
fat (T1 260 ms, T2 80 ms), white matter (T1 790 ms, T2 92 ms), CSF (T1 4000 ms, T2 2200 ms).
Contrast weighting depends on which term dominates — short TR emphasizes T1 differences, long TE emphasizes T2 differences.