Magnetic resonance characterization of blood coagulation in vitro: Effect of platelet depletion

To optimize magnetic resonance (MR) methods of characterizing thrombi, further studies of biologic determinants of spinlattice (Tl) and spin-spin (T2) relaxation times of thrombi are needed. As a step toward evaluating the influence of thrombus cellular composition on MR properties, the authors evaluated the effect of platelet depletion on MR relaxation times of in vitro blood clots. Blood from 13 fasting normal men was collected into sodium citrate (3.8%) and centrifuged ([10,000 X g] x 5-10 minutes). Platelet-poor specimens (&<20,000 per mm3) were reconstituted from the plasma and packed erythrocytes to match precentrifugation hematocrit levels. Tl and T2 measurements were made at 20 MHz within three to six hours of initiating clotting. The mean Tl value for platelet-rich (normal) specimens was 1117 ± 86 mseconds versus 1119 ± 68 mseconds for the platelet-poor specimens (P &> .90). The mean T2 value for platelet-rich (normal) specimens was 616 ± 130 mseconds versus 434 ± 79 mseconds for the platelet-poor specimens (P &< .001). The mean water content in the platelet-rich (normal) specimens was 79.5% ± 1.2% versus 80.0% ± 1.2% in the platelet-poor specimens (P &>.50). In summary, platelet depletion by buffy coat removal significantly shortens MR T2 values of in vitro clot. These data suggest that thrombus cellular composition, other than erythrocytes, alters MR relaxation times of clotted blood.