Imaging of Vascular Inflammation and Unstable Plaque
Imaging of Vascular Inflammation and Unstable Plaque
Targeted microbubbles have undergone experimental evaluation for visualizing cell surface structures implicated in plaque rupture. The compressible gas bubbles produce acoustic energy by resonating or releasing free gas when insonated. Most studies involving microbubble-based imaging agents have used antibodies as the targeting moiety. Other targeting strategies have involved the use of peptides and glycoproteins. Targets successfully visualized experimentally with contrast-induced ultrasound include leucocyte adhesion molecules such as intracellular adhesion molecule-1, VCAM-1, and P-selectin (Figure 1). Antibodies that recognize glycoprotein IIb/IIIa or peptides that contain the RGD sequence have succeeded experimentally in imaging activated platelets in thrombi. Targeting integrins such as αvβ3 also may serve to visualize microvessels. Unlabelled microbubbles can delineate neovascular channels in atherosclerotic plaques or the surrounding adventitia, providing another window on the characteristics associated with plaques at high risk of rupture.
Limitations of contrast-enhanced ultrasound include the short half-life of these bubbles in vivo, their restriction to the intravascular compartment, and the low contrast-to-noise ratio. Advantages include the very large installed base of ultrasound apparatuses, and the familiarity of this modality to practicing clinicians. Moreover, the lack of ionizing radiation also renders this approach attractive for routine clinical use.
Contrast-Enhanced Ultrasonography
Targeted microbubbles have undergone experimental evaluation for visualizing cell surface structures implicated in plaque rupture. The compressible gas bubbles produce acoustic energy by resonating or releasing free gas when insonated. Most studies involving microbubble-based imaging agents have used antibodies as the targeting moiety. Other targeting strategies have involved the use of peptides and glycoproteins. Targets successfully visualized experimentally with contrast-induced ultrasound include leucocyte adhesion molecules such as intracellular adhesion molecule-1, VCAM-1, and P-selectin (Figure 1). Antibodies that recognize glycoprotein IIb/IIIa or peptides that contain the RGD sequence have succeeded experimentally in imaging activated platelets in thrombi. Targeting integrins such as αvβ3 also may serve to visualize microvessels. Unlabelled microbubbles can delineate neovascular channels in atherosclerotic plaques or the surrounding adventitia, providing another window on the characteristics associated with plaques at high risk of rupture.
Limitations of contrast-enhanced ultrasound include the short half-life of these bubbles in vivo, their restriction to the intravascular compartment, and the low contrast-to-noise ratio. Advantages include the very large installed base of ultrasound apparatuses, and the familiarity of this modality to practicing clinicians. Moreover, the lack of ionizing radiation also renders this approach attractive for routine clinical use.
