Differentiation Of Red And White Thrombi With MRI-a Phantom Study

Objective:To study the possibility of differentiating acute red and white thrombi in vitro with MRI techniques.Materials and methods:Red thrombus samples were made from normal clotted whole blood and white thrombus samples from clotted platelet-enriched plasma. Both types of the thrombus were cut into small pieces with different sizes. All samples were imbedded into2%(g/ml) agar and kept at room temperature (about20℃) under aerobic condition for24hours. Then they were scanned with1.5T and3.0T MR imaging systems. The sequences consisted of Flair T1WI, T2WI, Flair T2WI, GRE T2*WI and susceptibility weighted angiography (SWAN). The signals of these red and white thrombi on both MR systems were explored and compared, focusing on the extremely low sinals caused by the susceptibility effect (SE).Statistical analyses were performed for the volume differences between the thrombi with different signals. Results:A total of12red and12white thrombi were produced. Except the three small samples on T2WI with3.0T MR showing hypo-intensity without SE, white thrombi manifested hyper-or iso-intensity on every sequence with the both MR systems. The average volumes of hyper-intensity white thrombi were larger than those of iso-or hypo-intensity ones on every sequence under both MR systems with statistical significances(every P<0.05), except for T2WI under3.0T(P>0.05). The three larger red thrombi were found SE on GRE T2*WI and SWAN under both MR systems with statistical significances of the volume differences(every P<0.05). While other9red thrombi, except one on Flair T1WI and7on GRE T2*WI with1.5T depicting iso-intensity, were hyper-intensity on every sequence with both MR systems. Being lower signal and wider extent, SE under3.0T depicted more obviously than under1.5T, and on SWAN than on GRE T2*WI.Conclusion:Differentiation of red and white thrombus with conventional MR sequence is unreliable, because both kinds of thrombus do not possess unique signal intensity features on these sequences. White thrombus does not show SE at all, while some red thrombi may show SE on the susceptibility sensitive MR sequences. The volum of red thrombus has influence on its SE, which may caused by its concentration of deoxyhemoglobin. As to the depiction of SE,3.0T is superior to1.5T, and SWAN superior to GRE T2*WI.