Effect of externally applied focused acoustic energy on clot disruption invitro

Application of low-frequency ultrasound for clot disruption has been sugges ted as a potential therapy to enhance th rom bus dissolution, but the optim al mode: for delivery of ultrasound with clot-disruptive properties has not yet been extensively explored. Target-specific effects are desirable and m ay be accomplished by focusing the ultrasound. Adequate focusing, however, requires a short wavelength. The aim of this study was to compare the clot- disruptive effects of different modalities of focused acoustic.. energy. An in vitro model (10 blood clots for each modality) was used to test the clo t-disruptive capacity of (i) shock waves generated in an electrohydraulic l ithotriptor; (ii) focused continuous ultrasound of frequency 1.1 MHz, deliv ered from a specially constructed piezoelectric transducer; and (iii) focus ed pulse-modulated ultrasound of frequency 1.1 MHz delivered from the same transducer. Exposure to 30 s of focused pulse-modulated ultrasound caused a , marked reduction (99+/-2%) in clot weight compared with 30 shock waves (1 1 +/- 5%) or 30 s exposure to focused continuous wave ultrasound (11 +/- 6% ) (P < 0.0001). The observed marked and rapid disruptive effect on blood cl ots of focused high-frequency ultrasound indicates an alternative approach for external ultrasound-mediated thrombus destruction in vivo. The focused pulse-modulated technique has potential to exhibit the desired effect in a well-defined target volume and provides the means for control of the averag e power.