Dayton P, Klibanov A, Brandenburger G, Ferrara K
Department of Biomedical Engineering, University of Virginia, Charlottesville 22908, USA.
Ultrasound Med Biol. 1999 Oct;25(8):1195-201. doi: 10.1016/s0301-5629(99)00062-9.
The goal of targeted imaging is to produce an enhanced view of physiological processes or pathological tissue components. Contrast agents may improve the specificity of imaging modalities through selective targeting, and this may be particularly significant when using ultrasound (US) to image inflammatory processes or thrombi. One means of selective targeting involves the attachment of contrast agents to the desired site with the use of a specific binding mechanism. Because molecular binding mechanisms are effective over distances on the order of nanometers, targeting effectiveness would be greatly increased if the agent is initially concentrated in a particular region, and if the velocity of the agent is decreased as it passes the potential binding site. Ultrasonic transmission produces a primary radiation force that can manipulate microbubbles with each acoustic pulse. Observations demonstrate that primary radiation force can displace US contrast agents from the center of the streamline to the wall of a 200-microm cellulose vessel in vitro. Here, the effects of radiation force on contrast agents in vivo are presented for the first time. Experimental results demonstrate that radiation force can displace a contrast agent to the wall of a 50-microm blood vessel in the mouse cremaster muscle, can significantly reduce the velocity of flowing contrast agents, and can produce a reversible aggregation. Acoustic radiation force presents a means to localize and concentrate contrast agents near a vessel wall, which may assist the delivery of targeted agents.
靶向成像的目标是增强对生理过程或病理组织成分的观察。造影剂可通过选择性靶向提高成像模态的特异性，在使用超声（US）对炎症过程或血栓进行成像时，这一点可能尤为重要。选择性靶向的一种方法是利用特定的结合机制将造影剂附着到所需部位。由于分子结合机制在纳米级距离上有效，如果造影剂最初集中在特定区域，并且当其通过潜在结合位点时速度降低，靶向效果将大大提高。超声传输会产生一个初级辐射力，每次声脉冲都能操纵微泡。观察表明，在体外，初级辐射力可将超声造影剂从流线中心位移到200微米纤维素血管的壁上。在此，首次展示了辐射力对体内造影剂的影响。实验结果表明，辐射力可将造影剂位移到小鼠提睾肌中50微米血管的壁上，可显著降低流动造影剂的速度，并可产生可逆聚集。声辐射力提供了一种在血管壁附近定位和浓缩造影剂的方法，这可能有助于靶向剂的递送。
