AN IN-VITRO STUDY OF MAGNETIZATION-TRANSFER AND RELAXATION RATES OF HEMATOMA

PURPOSE: To assess, in an in vitro model of acute hematoma, whether he moglobin immobilization by clot and red cell membrane aging can accoun t for the T2 shortening usually attributed to deoxyhemoglobin. METHODS : Clotted and heparinized blood samples were packed (100% hematocrit). The apparent magnetization transfer rate (AMTR), T1 and T2 relaxation rates of the samples, and images with a volunteer's head were obtaine d at 1.5 T. RESULTS: The AMTR and T1 and T2 relaxation rates were unaf fected by the presence of clot. The AMTR was unaffected by red cell ag ing. The diamagnetic packed blood samples, which are much denser than brain, were isointense to gray matter on T2-weighted images and had ab out one-fifth the AMTR of white matter. CONCLUSIONS: Hemoglobin immobi lization by clot structure or red cell contraction with aging is insig nificant and does not contribute to the T2 shortening of acute hematom a. The low AMTR and T2 relaxation rates of diamagnetic blood appear to be caused by the mobility of hemoglobin and by the red cell's lack of immobile macromolecular structures such as those associated with nucl eated brain cells.