Figure 4. (a) The "penumbra sign" in subacute osteomyelitis. Coronal T₁ weighted image of the hindoot demonstrating an intermediate signal rim (arrow) around a central area of lower signal intensity indicating an intra-osseous abscess in the talus. (b) Coronal short tau inversion recovery (STIR) image demonstrating a fluid signal collection in the talus consistent with an abscess.