MR imaging of cerebral hematomas at different field strengths: theory and applications.

Existing theory on relaxation effects in blood and their field dependence is related to magnetic resonance (MR) imaging of hematomas. These effects include (a) relaxation caused by protein and other macromolecules; (b) inhomogeneous susceptibility created by paramagnetic forms of hemoglobin (Hb) (deoxy and met) within the red blood cells; and (c) direct interaction of water protons with paramagnetic metHb. The effect of proton density is also discussed. These effects combine in a complex way to create hypo- or hyper-intensity on MR images of hematomas. Further, the effects change as the hematoma evolves both physically and chemically. In particular, there are five stages that are associated with typical image appearance: (a) oxygenated blood; (b) deoxygenated blood; (c) conversion to metHb; (d) hemolysis; and (e) protein resorption.