MAGNETIZATION-TRANSFER EFFECTS IN MR-IMAGING OF IN-VIVO INTRACRANIAL HEMORRHAGE

PURPOSE: Recent papers have hypothesized that diamagnetic effects of c lotting and conformational changes in aging red blood cells immobilize the hemoglobin protein and thus are responsible for the marked hypoin tensity of acute hematomas on T2-weighted spin-echo MR images. To test that hypothesis, the authors evaluated 24 hemorrhagic components of i ntracranial hemorrhagic lesions using accepted criteria based on spin- echo images as the definitions of the stage of the hemorrhage. METHODS : As a measure of the effects of macromolecular (hemoglobin protein) i mmobility, magnetization transfer contrast was elicited using a pulsed saturation magnetization transfer experiment. The apparent magnetizat ion transfer contrast (AMTC) was determined by comparing the signal in tensities of saturated with unsaturated images and quantified for acut e isolated hemorrhages, acute nonisolated hemorrhagic lesions, and sub acute-to-chronic hemorrhages. RESULTS: The AMTC of isolated acute hemo rrhage was significantly less than that of normal white matter and gra y matter, indicating the lack of significant magnetization transfer an d therefore the lack of effects of restriction of hemoglobin mobility on the signal intensity of acute hemorrhage. Acutely hemorrhagic tissu e (nonisolated acute hemorrhage) has significantly more AMTC than isol ated acute hemorrhage, but still not exceeding that of brain parenchym a. CONCLUSION: This in vivo data concurs with in vitro data and reinfo rces the concept that the marked hypointensity of acute hematomas is m ainly a magnetic susceptibility effect.