Objective:To evaluate the impact of the diameter of SonoVue microbubbles on binding characteristics, including the adhesion rate and stability, of a new contrast agent targeted to choriocarcinoma cells(JARs) in vitro, in order to establish a foundation to explore targeted ultrasound imaging for localization of tumor cell antigens and increase the early diagnostic rate for tumors.Methods:The objects were divided into three groups:the large microbubble group(n = 15), the middling microbubble group(n = 15) and the tiny microbubble group(n = 15).The rosette formation rate was counted.JARs were calculated by flow cytometry(FCM).The targeted contrast agent was prepared by mixing SonoVue microbubbles of different diam-eter with rabbit anti-human chorionic gonadotrophin(HCG) antibody.The binding rates of the targeted contrast agent to JARs before and after PBS rinse were analyzed.Results:The binding rate was significantly lower in the large microbubble group(61.7 ± 1.8)% than in the middling microbubble group(82.6 ± 4.5)% and the tiny microbubble group(91.3 ± 5.8)%(P < 0.05).The binding rates of different diameter microbubbles to JARs before and after PBS rinse were different.The middling microbubbles were the most stable ones, with the binding rate of(82.3 ± 4.5)% and(80.4 ± 3.9)% before and after PBS rinse(P > 0.05).The binding rates of the targeted microbubbles labeled with fluorescence to JARs were 68.6%, 81.3% and 89.3% in the large microbubble group, the middling microbubble group and the tiny microbubble group, respectively(P < 0.05).Conclu-sion:The binding capacity of the targeted SonoVue microbubbles to JARs is related to the diameter of the microbubble, which is determined by the shaking method before preparation.Modulating the diameter of SonoVue microbubbles may increase the binding rate and stability of targeted microbubbles to JARs, thus to improve the image of JARs. Objective: To evaluate the impact of the diameter of SonoVue microbubbles on binding characteristics, including the adhesion rate and stability, of a new contrast agent targeted to choriocarcinoma cells (JARs) in vitro, in order to establish a foundation to explore targeted ultrasound imaging for localization of tumor cell antigens and increase the early diagnostic rate for tumors. Methods: The objects were divided into three groups: the large microbubble group (n = 15), the middling microbubble group (n = 15) and the tiny microbubble group . 15). The targeted contrast agent was prepared by mixing SonoVue microbubbles of different diam-eter with rabbit anti-human chorionic gonadotrophin (HCG) antibody. The antibody rates of the targeted contrast agent to JARs before and after PBS rinse were compared. Results: The binding rate was significantly lower in the large microbubble group (61.7 ± 1.8)% than in the middling microbubble group (82.6 ± 4.5)% and the tiny microbubble group (91.3 ± 5.8)% (P <0.05). The binding rates of different diameter microbubbles to JARs before and after PBS rinse were different. The middling microbubbles were the most stable ones , with the binding rate of (82.3 ± 4.5)% and (80.4 ± 3.9)% before and after PBS rinse (P> 0.05). The binding rates of the targeted microbubbles labeled with fluorescence to JARs were 68.6%, 81.3% and 89.3 % in the large microbubble group, the middling microbubble group and the tiny microbubble group, respectively (P <0.05) .Conclu-sion: The binding capacity of the targeted SonoVue microbubbles to JARs is related to the diameter of the microbubble, which is determined by the shaking method before preparation. Modulating the diameter of SonoVue microbubbles may increase the binding rate and stability of targeted microbubbles to JARs, thus to improve the image of JARs.