Magnetic resonance imaging (MRI) has established itself as a valuable tool for bone marrow imaging.1–3It has proven to be the most sensitive technique available for imaging a variety of bone marrow disorders, in many cases with sensitivity comparable or superior to nuclear medicine studies and resolution rivaling computed tomography (CT).The sensitivity of MRI to changes in bone marrow is due to the inherent properties of MRI. Signal intensity in MR images largely results from the combination of relaxation properties and the concentration and chemical form of mobile protons. Perhaps in no other organ of the body is MR signal intensity so profoundly influenced by the relative concentrations of fat and water as in the bone marrow. Paramagnetic and superparamagnetic effects are also important in the genesis of MR signal intensity changes, as the bone marrow is critically involved in storage and processing of iron.