The MR appearance of intracranial hemorrhage is a function qf many factors, including time, etiology, anatomic comnpartment, drugs, and svstemic or local metabolic conditions (e.g., pO2, pH). The complexity qf the subject can seem overwhelming to those not well grounded in the phvsics qf MR. In addition, the physical principles influencing the MR appearance ofhetnatoma are mzdtijactoriul and as yet incomnpletely iinderstood. From a practicing radiologist's standpoint, this lesson provides the basic information needed to recognize the itsual appearance of intracerebral hemorrhage in its varying nianifestations, so that an accurate interpretation may be rendered.
It is helgfiil to begin by recalling some of the basic aspects of magnetic resonance image production. First, the soiirce of all MR signal (and hence the image) is the hvdrogen proton. which in the brain means mostly the hydrogen found in water. Secondly, variations in MR contrast and signal intensity result from any phenomenon which (1) alters the T1 relasation time ojthe proton, (2) alters the T2 relaxation time of a volume of protons, or (3) alters the local concentration of protons (proton density). Accordingly, hemoglobin and its products yield no significant signal of their own, but they munifest their appearance by specific effect upon their watery environment.