Summary
Ultrasound and microbubble (MB) contrast agents accelerate clot lysis, yet clinical
trials have been performed without defining optimal acoustic conditions. Our aim was
to assess the effect of acoustic pressure and frequency on the extent and spatial
location of clot lysis. Clots from porcine blood were created with a 2-mm central
lumen for infusion of lipid-shelled perfluorocarbon MBs (1×107 ml-1) or saline. Therapeutic ultrasound at 0.04, 0.25, 1.05, or 2.00 MHz was delivered
at a wide range of peak rarefactional acoustic pressure amplitudes (PRAPAs). Ultrasound
was administered over 20 minutes grouped on-off cycles to allow replenishment of MBs.
The region of lysis was quantified using contrast-enhanced ultrasound imaging. In
the absence of MBs, sonothrombolysis did not occur at any frequency. Sonothrombolysis
was also absent in the presence of MBs despite their destruction at 0.04 and 2.00
MHz. It occurred at 0.25 and 1.05 MHz in the presence of MBs for PRAPAs > 1.2 MPa
and increased with PRAPA. At 0.25 MHz the clot lysis was located in the far wall.
At 1.05 MHz, however, there was a transition from far to near wall as PRAPA was increased.
The area of clot lysis measured by ultrasound imaging correlated with that by micro-CT
and quantification of debris in the effluent. In conclusion, sonothrombolysis with
MBs was most efficient at 0.25 MHz. The spatial location of sonothrombolysis varies
with pressure and frequency indicating that the geometric relation between therapeutic
probe and vascular thrombosis is an important variable for successful lysis clinically.
Supported by grant (NIH R01-HL-095868).
Keywords
Thrombolysis / thrombolytic agents - ultrasound analysis - imaging