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目的:通过调控脉冲重复频率(PRF)探讨诊断超声的不同占空比对增强乏血供肿瘤血流灌注的影响。方法:选用SD大鼠15只，于大腿内侧皮下建立Walker-256肿瘤模型，根据PRF随机分为3组，每组5只：A组，PRF＝50 Hz；B组，PRF＝1.0 kHz；C组，PRF＝2.0 kHz。每组荷瘤大鼠经超声联合微泡治疗10 min，于治疗前、治疗后即刻、治疗后4 h分别行超声造影检查，比较各组峰值强度(PI)、曲线下面积(AUC)和肿瘤血流灌注面积。结果:治疗后即刻，A、B组的PI、AUC值较治疗前增加(均n P<0.05)；治疗后4 h，B组PI、AUC值持续增加，优于治疗后即刻(均n P0.05)。治疗后即刻，A、B组肿瘤血流灌注面积较治疗前增加(均n P<0.05)；治疗后4 h，B组的肿瘤血流灌注面积持续增加，优于治疗后即刻(n P0.05)。n 结论:PRF＝1.0 kHz的低强度诊断超声激励微泡空化可产生较明显的肿瘤血流增强效应，且持续4 h以上。“,”Objective:To study the effects of different duty cycles [modulated by pulse repetition frequency(PRF)] of diagnostic ultrasound on enhancing blood perfusion in hypovascular tumors.Methods:Walker-256 tumor cells were injected subcutaneously into the inner thigh of 15 SD rats, and the rats were randomly divided into 3 groups according to PRF: group A(PRF=50 Hz), group B(PRF=1.0 kHz) and group C(PRF=2.0 kHz), with 5 rats in each group. The tumor-bearing rats in each group were treated with ultrasound combined with microbubbles for 10 minutes. Contrast-enhanced ultrasound was performed before treatment, immediately after treatment, and 4 hours after treatment, respectively, to compare the peak intensity(PI), area under curve(AUC), and tumor perfusion area in each group.Results:Immediately after treatment, PI and AUC values of group A and B increased compared with those before treatment (all n P<0.05); 4 hours after treatment, PI and AUC values of group B continued to increase, superior to that immediately after treatment (alln P0.05). Immediately after treatment, the tumor blood perfusion area in group A and B increased significantly compared with that before treatment (alln P<0.05); 4 hours after treatment, the tumor blood flow perfusion area of group B continued to increase, which was better than that immediately after treatment (n P0.05).n Conclusions:Low-intensity diagnostic ultrasound stimulated microbubble cavitation with PRF=1.0 kHz can enhance tumor blood flow significantly which can last for more than 4 hours.