The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
Ultrason Sonochem. 2023 Dec;101:106665. doi: 10.1016/j.ultsonch.2023.106665. Epub 2023 Oct 29.
Understanding the behavior of nanodroplets converted into microbubbles with applied ultrasound is an important problem in tumor therapeutical and diagnostic applications. In this study, a comprehensive model is proposed to investigate the vaporization process and the direct growth threshold of the nanodroplet by following the vapor bubble growth, especially attention devoted to the effect of tissue viscoelasticity and adjacent phase-changed microbubbles (PCMBs). It is shown that the ultrasonic energy must be sufficiently strong to counterbalance the natural condensation of the vapor bubble and the tissue stiffness-inhibitory effect. The softer tissue with a lower shear modulus favors the vaporization process, and the nanodroplet has a lower direct growth threshold in the softer tissue. Moreover, the adjacent PCMBs show a suppression effect on the vaporization process due to the negative value of the secondary Bjerknes force, implying an attractive force, preventing the nanodroplet from escaping from the constraint of the adjacent PCMBs. However, according to the linear scattering theory, the attractive force signifies that the constraint is weak, causing the direct growth threshold to increase in the range of 0.09-0.24 MPa. The weak increase in threshold demonstrates that the direct growth threshold is relatively unaffected by the adjacent PCMBs. The prediction results of our model are in good agreement with the experiment results obtained by the echo enhancement method, in which the threshold is relatively independent of the intermediate concentration. The findings presented here provide physical insight that will be further helpful in understanding the complex behavior of the nanodroplet responses to ultrasound in practical medical applications.
理解应用超声将纳米液滴转化为微泡的行为是肿瘤治疗和诊断应用中的一个重要问题。在这项研究中，提出了一个综合模型来研究纳米液滴的蒸发过程和直接生长阈值，特别是关注组织粘弹性和相邻相变微泡（PCMBs）的影响。结果表明，超声能量必须足够强，以抵消蒸汽泡的自然凝结和组织刚度抑制效应。较软的组织具有较低的剪切模量，有利于蒸发过程，并且较软的组织中的纳米液滴具有较低的直接生长阈值。此外，由于二次 Bjerknes 力的负值，相邻的 PCMBs 对蒸发过程表现出抑制作用，暗示存在吸引力，防止纳米液滴从相邻 PCMBs 的约束中逃脱。然而，根据线性散射理论，吸引力表明约束较弱，导致直接生长阈值在 0.09-0.24 MPa 的范围内增加。阈值的微弱增加表明，直接生长阈值受相邻 PCMBs 的影响相对较小。我们模型的预测结果与回声增强法获得的实验结果吻合较好，其中阈值相对独立于中间浓度。这里提出的研究结果提供了物理洞察力，将有助于进一步理解纳米液滴对超声响应的复杂行为在实际医学应用中的表现。
