VIDEO 1.

T1‐STIR (short tau inversion recovery) matching. First slide, T1 features: compartmental heatmaps of fat replacement (left panel), fat replacement in thighs (right, top) and unreplaced proximal‐distal legs (right, bottom). Second slide: STIR features: compartmental heatmaps of STIR‐positive muscles (left panel), STIR positivity in thighs (right, top) and legs (right, bottom). Note that STIR positivity occurs in the same areas of the heatmap with overall higher T1 scores in the thighs and legs, and the STIR‐positive signal is evident in still unreplaced muscle areas (Mercuri score <4) (thighs) and in still unreplaced muscles with distal‐proximal gradient (legs), suggesting that STIR positivity precedes the fat replacement