Barrack Thomas, Stride Eleanor
Department of Mechanical Engineering, University College London, London, UK.
Ultrasound Med Biol. 2009 Mar;35(3):515-22. doi: 10.1016/j.ultrasmedbio.2008.07.008. Epub 2008 Dec 24.
The concentration and size distribution of microbubble suspensions are important parameters for both diagnostic and therapeutic applications. The aim of this preliminary study was to investigate the relationship between changes in the microbubble population and the administration process variables, specifically syringe inner diameter, needle inner diameter, volume flow rate and the liquid in which the microbubbles are suspended. It was found that reducing either the syringe or needle inner diameter produced large reductions in microbubble concentration during administration, as much as 99.9% for needle inner diameters <0.24 mm. Increasing the volume flow rate up to 3 mL/min and changing the suspending fluid from distilled water to glycerol, however, were both found to reduce the degree of microbubble destruction. Further work is needed to fully explain these observations. However, investigation of the response of microbubbles to changes in hydrostatic pressure only, indicated that this was unlikely to be the main mechanism of destruction and hence that shear stress was a more important factor. Comparison with findings from another recent study of microbubble stability indicated that microbubble size, concentration and composition were also important parameters and should be taken into account in designing administration procedures for microbubble agents. It was concluded that current procedures should be reviewed, particularly for therapeutic applications, and that the results should also be taken into account when assessing the accuracy of microbubble size distribution measurements obtained using automatic particle sizing equipment in which microbubbles are made to flow under pressure.
微泡悬浮液的浓度和大小分布对于诊断和治疗应用来说都是重要参数。这项初步研究的目的是调查微泡数量的变化与给药过程变量之间的关系，具体包括注射器内径、针内径、体积流速以及微泡所悬浮的液体。研究发现，在给药过程中，减小注射器或针的内径会使微泡浓度大幅降低，对于内径小于0.24毫米的针，微泡浓度降低幅度高达99.9%。然而，将体积流速提高到3毫升/分钟以及将悬浮液从蒸馏水换成甘油，均被发现可降低微泡的破坏程度。需要进一步开展工作来充分解释这些观察结果。不过，仅对微泡对静水压力变化的响应进行研究表明，这不太可能是主要的破坏机制，因此剪切应力是一个更重要的因素。与另一项近期关于微泡稳定性的研究结果相比，表明微泡大小、浓度和组成也是重要参数，在设计微泡剂给药程序时应予以考虑。得出的结论是，应重新审视当前的程序，尤其是针对治疗应用的程序，并且在评估使用自动颗粒大小测量设备在压力下使微泡流动所获得的微泡大小分布测量的准确性时，也应考虑这些结果。
