B-mode sonography of blood clots.

Systematic evaluation of blood clot echogenicity was performed with five different transducer frequencies in two experiments. In the first experiment, blood clots were insonified at five different time periods; from immediately after clotting up to 96 hours after clotting. In the second experiment, blood clots of four different hematocrits (48 to 20%) and clots of hemolysed blood were insonified. The clots, with normal hematocrits, were highly echogenic when imaged with 5, 7.5 and 10-MHz transducers immediately and 24 hours after clotting. The echo intensity decreased over the following days until it almost disappeared at 96 hours after clotting. Clot echogenicity was not observed with 2.25 and 3.5-MHz transducers, except at the interface between retracted clot and serum. Clot echogenicity decreased in proportion with the hematocrit. Hemolysed blood clots were not echogenic. It is concluded from this study that fresh blood clots are echogenic soon after thrombosis with high resolution imaging and this echogenicity diminishes with time. Ultimately with organization and lamination, echogenicity will recur.