What are the MRI characteristics of hemosiderin and ferritin in chronic hemorrhage (greater than 21 days) on T1 and T2-weighted images, and what is the state of red blood cells in this phase?

In chronic hemorrhage, occurring more than 21 days after the event, red blood cells are lysed, and hemosiderin and ferritin are present. On MRI, this results in a hypointense (dark) signal on both T1 and T2-weighted images due to the paramagnetic effects of hemosiderin. Key diagnostic features include the presence of a dark rim on susceptibility-weighted imaging (SWI), which helps differentiate it from other lesions. A common pitfall is mistaking hemosiderin deposition for calcification, which can be avoided by correlating with CT findings.