Coussios Constantin-C, Holland Christy K, Jakubowska Ludwika, Huang Shao-Ling, MacDonald Robert C, Nagaraj Ashwin, McPherson David D
Department of Biomedical Engineering, University of Cincinnati, Cincinnati, OH, USA.
Ultrasound Med Biol. 2004 Feb;30(2):181-90. doi: 10.1016/j.ultrasmedbio.2003.10.015.
Liposomes are phospholipid vesicles that can encapsulate both gas and fluid. With antibody conjugation, new formulations, known as immunoliposomes, can be targeted to atheroma and other pathologic components and are, thus, being developed as novel diagnostic ultrasound (US) echo contrast agents to enhance atherosclerosis imaging. The majority of these echogenic liposomes range in diameter from 0.25 to 5.0 microm. To quantify the echogenicity of liposome suspensions of varying concentrations, the backscattering coefficient at 3.5 MHz was determined experimentally. The backscattering coefficient was also estimated theoretically as a function of air volume fraction by modeling the encapsulated air as a free air bubble and assuming single bubble scattering. For most of the liposome concentrations examined in this study (on the order of 10(8)/mL), the backscattering coefficient equals or exceeds that of Optison at the human clinical dosage (on the order of 10(4)/mL). Experimental measurement of the decrease in backscattering coefficient shows promise as a sensitive method for determining whether liposomes are left intact or destroyed during imaging; thus, helping to explore their potential as a vehicle for targeted drug delivery. In addition, the attenuation of US through liposome suspensions is negligible at 3.5 MHz relative to the attenuation through Optison (0.25 dB/cm), suggesting that liposomes have a much higher scatter-to-attenuation ratio and could be more efficient as contrast agents.
脂质体是一种磷脂囊泡，能够包裹气体和液体。通过与抗体结合，可以制备出一种名为免疫脂质体的新型制剂，该制剂能够靶向动脉粥样硬化斑块及其他病理成分，因此正被开发为新型诊断超声（US）造影剂，以增强动脉粥样硬化成像。这些大多数的回声脂质体直径范围在0.25至5.0微米之间。为了量化不同浓度脂质体悬浮液的回声性，通过实验测定了3.5兆赫兹时的后向散射系数。通过将包裹的空气模拟为自由气泡并假设单气泡散射，理论上还将后向散射系数估计为空气体积分数的函数。对于本研究中检测的大多数脂质体浓度（约为10⁸/mL），其在人体临床剂量（约为10⁴/mL）下的后向散射系数等于或超过Optison的后向散射系数。后向散射系数降低的实验测量结果显示，它有望成为一种灵敏的方法，用于确定脂质体在成像过程中是否保持完整或被破坏；从而有助于探索其作为靶向药物递送载体的潜力。此外，相对于通过Optison（0.25分贝/厘米）的衰减，3.5兆赫兹时超声在脂质体悬浮液中的衰减可忽略不计，这表明脂质体具有更高的散射与衰减比，作为造影剂可能更有效。
