Abstract 349: The Effects of Attenuation and Thrombus Age on the Success of Ultrasound and Microbubble Mediated Thrombolysis
Background. Although ultrasound and intravenous microbubbles (MB) have been used in recanalizing intravascular thrombi, the success rate clinically may depend on the age of the thrombus and the degree of ultrasound attenuation that occurs. The purpose of this study was to examine the effects of attenuation and clot age on the ability of diagnostic ultrasound and MB to dissolve thrombi without the aid of a fibrinolytic agent.
Methods. A total of 100 porcine arterial thrombi of varying age (3 or 6 hours) were treated with two-dimensional (2D) or three-dimensional (3D) ultrasound. Occlusive thrombi were embedded in branching silastic vessels (2 mm internal diameter) suspended in a tank containing water at 37° C. Flow within the vessel was monitored using a flow pump (MasterFlex). A tissue-mimicking phantom (TMP) of varying thickness (5–10 cm) was placed over the thrombosed vessel and the 2D (S 5–1 sector array) or 3D (X 3–1 xMATRIX array) transducer (Philips iE 33) aligned with the thrombosed vessel using a positioning system. Ten treatment groups were analyzed that varied in clot age, TMP thickness, and transducer types. Diluted lipid encapsulated MB (0.5% Definity; Lantheus, North Billerica, MA) were imaged with each transducer using low MI imaging (Power Modulation) at <0.2 MI which then guided the timing of the high MI impulses (>1.0) with either transducer. Total treatment time was 10 minutes. Percent thrombus dissolution (%TD) was calculated by comparison of clot mass before and after treatment.
Results. Both 2D and 3D guided ultrasound increased % TD compared to MB alone, irrespective of thrombus age or attenuation (Table⇓). However, %TD achieved with six hour old thrombi was significantly less than three hour old thrombi.
Conclusions. Diagnostic 2D or 3D ultrasound can dissolve thrombi with intravenous non-targeted MB even at tissue attenuation distances of up to 10 centimeters. This treatment modality is less effective, however, for older thrombi.