Heart, Lung and Circulation

Molecular Imaging of Acute Thrombosis and Thrombolysis by Contrast Enhanced Ultrasound with Novel Platelet-targeted Microbubbles

      Background: Molecular imaging is a rapidly emerging enabling technology allowing non-invasive detection of vascular pathologies. However, imaging technologies offering a high resolution are currently not inherently real-time applications. We hypothesised that contrast enhanced ultrasound (CEU) with microbubbles selectively targeted to activated platelets would offer real-time molecular imaging of evolving arterial thrombosis.
      Methods and results: Lipid-shell based air-filled microbubbles were conjugated to either a single-chain antibody (scFv) specific for activated GPIIb/IIIa (LIBS-MB), or a non-specific scFv (control-MB). Flow-chamber experiments demonstrated strong adhesion of LIBS-MB to immobilised activated platelets at 50 s−1 compared with control-MB (84 ± 10 vs 15 ± 2; p < 0.001). Increasing the shear rate to 1000s−1 and 6000s−1 dislodged most control-MB while LIBS-MB remained strongly attached (p < 0.001). Platelet-rich thrombi were induced in carotid arteries of C57Bl6-mice in vivo by ferric chloride injury. Thrombi were then assessed with CEU-imaging before and 20 minutes after microbubble injection. Thrombosis was detected via the greyscale area, which was strongly increased after LIBS-MB but not after control-MB injection (214.25 ± 33.5 vs 9.96 ± 10.38; p < 0.001). After thrombolysis with urokinase, CEU-imaging showed a significant reduction in thrombus size (p < 0.001).
      Conclusions: We are able to demonstrate that our targeted microbubbles specifically bind to activated platelets in vitro and allow real-time molecular imaging of acute arterial thrombosis as well as monitoring pharmacological thrombolysis in vivo. This non-invasive and cost effective imaging modality provides a unique opportunity to detect arterial (micro)thrombi at an early stage allowing for early diagnosis and therapy.