Abstract 2900: Detection of Intravascular Cavitational Activity during Treatment of Deep Vessel Thromboses with Diagnostic Ultrasound and Intravenous Microbubbles
Background. A low frequency diagnostic ultrasound transducer (DUT) and intravenous microbubbles (MB) can induce recanalization of acutely thrombosed vessels when using high mechanical index (MI) impulses. The mechanism for thrombus dissolution is unknown. We sought to determine whether cavitation occurs within thrombosed vessels containing MB, and whether this is associated with recanalization.
Methods. A total of 35 arteriovenous graft thromboses in the femoral region of 2 dogs were compared. Nine served as controls (ultrasound alone), while the remainder received a continuous intravenous infusion of MB (MRX 801). A transcutaneous DUT (1.5 MHz) was used to detect microbubble transit through the thrombus at a low MI of <0.3 (Contrast Pulse Sequencing; Siemens Acuson), at which time brief high MI impulses were applied (1.9 MI). Angiographic recanalization rates were compared between the two groups (total treatment time 45 minutes). In two additional graft thromboses, a 20 MHz cavitation detector was placed adjacent to the diagnostic ultrasound transducer so that the detector focus point was within the intravascular thrombus, and recordings of cavitational activity (CA) within the thrombosed vessel were obtained at six time intervals of ultrasound application (between 6 and 45 minutes). In these two studies, the MI of the brief high MI impulses ranged from 0.3 to 1.9.The CA (root-mean-squared voltage in mV) within the graft was correlated with the degree of recanalization achieved by conventional angiography.
Results. Recanalization rates were 73 % in grafts treated with intermittent high MI impulses, compared to 33 % in controls (p=0.04). CA was detected within the graft at brief high MI impulses >0.5 MI, with the degree of CA increasing as flow and microbubble concentration within the vessel increased. CA within the vessel decreased significantly when the MI of the brief impulses dropped to <0.5 MI (1.1 ± 1.1 mV at <0.5 MI versus 3.5 ± 0.6 mV at MI>0.5; p<0.001).
Conclusion. During continuous infusions of intravenous MB, a DUT induces intravascular cavitation within thrombosed grafts at brief high MI impulses exceeding 0.5.These brief bursts of cavitation may play a vital role in ultrasound and microbubble-induced thrombus dissolution.