The first image shows the penumbra rim eliciting a high signal on non-enhanced T1 WI and intense post-contrast enhancement (yellow arrows).
The second image shows the characteristic four-layered appearance of an abscess consisting of
- a centre with low T1 and high T2 signal (white arrow)
- an inner ring with muscle signal intensity on T1 and low intensity on T2 (yellow arrow)
- an outer ring of fibrotic reaction with low signal intensity on T1 and T2 (blue arrow)
- a peripheral halo of bone marrow oedema with low signal intensity on T1 and variable signal intensity on T2 (red arrow)