Imaging targeted microbubble interactions with microvessels

High-speed imaging was used to directly observe the dynamics of targetedmicrobubbles in microvessels of ex vivo rat mesentery. Targeted microbubbleswere prepared by attaching biotinylated CD31 antibody to microbubbles that werecoated by straptavidin. Specific microbubbles were identified to be adherent tothe vessel wall. An ultrasound pulse of about 2 s long with peak negativepressure 0.8 MPa or 1.5 MPa interrogated the tissue sample as high-speedphotomicrographic images were acquired with 50-ns shutter speeds. Asymmetricaloscillation of adherent microbubbles was observed. At 0.8 MPa, the microbubbleremained attached to the vessel wall after exposure of a single ultrasoundpulse. However, at 1.5 MPa, microbubble oscillation induced obvious vessel walldistention and invagination, which was accompanied by microbubble detachment andtranslation away from the vessel wall. The formation of liquid jets was alsoobserved at 1.5 MPa. The adherence of targeted microbubbles to the vessel wallresulted in relatively strong interactions with the vessel walls at the higherultrasound pressure level. Lower pressure levels are needed to prolong theattachment of the microbubbles.