The marrow contains a variable amount of yellow or fatty marrow and red or cellular marrow creating the signal intensity observed on MRI. Marrow replacement (by cells not normally present in bone marrow) typically is T1W hypointense. Marrow proliferation (by cells normally present in bone marrow) may be T1W hypointense (pseudo marrow replacement) or show intermediate T1W signal intensity due to red marrow redistribution. Marrow edema (reaction to an external process) show intermediate T1W hypointensity (mixture of water and marrow). Location will allow correct diagnosis. Bone marrow ischemia usually results in a necrotic fragment surrounded by a thin T1W hypointense rim.