Adaptive radiation force ultrasound for monitoring hemostasis in whole blood

Over-activation or under-regulation of hemostasis plays a central role in the onset of diseases that represent leading causes of morbidity and mortality in the developed world. Current diagnostic technologies have had limited success in characterizing hemostasis due to several limitations including reagent variability, complicated sample preparation, and a disregard for contributions of cellular components of the blood. In this paper, we describe a novel technique, termed sonorheometry, which uses acoustic radiation force to monitor the dynamic changes in mechanical properties of whole blood during clot formation and dissolution in vitro. An adaptive force technique was used to adjust the pulse repetition frequency during each experiment, which improved the dynamic range of stiffness measurements to approximately five orders of magnitude. Experiments were performed to test the sensitivity of sonorheometry to platelet function, fibrinogen function, and fibrinolytic activity by titrating samples of whole blood with platelet inhibitor, Reopro (0-12 ¿g/mL); fibrinogen inhibitor, Gly-Pro-Arg-Pro (GPRP) peptide (0-8 mM); and plasminogen activator, Urokinase (0-200 Units). When 12 ¿g/mL of Reopro was added to samples of whole blood, clot stiffness, S_MAX decreased by over an order of magnitude. Similarly, clotting times (TC₁ and TC₂) were increased and clotting stiffness decreased with additional GPRP. Clot lysis times (TL₁ and TL₂) decreased with additional Urokinase. These results indicate that sonorheometry is sensitive to all phases of hemostasis.