The difference-frequency （DF） ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.
Microbubbles promise to enhance the efficiency of ultrasound-mediated drug delivery and gene therapy by taking advantage of artificial cavitation nuclei. The purpose of this study is to examine the ultrasound-induced hemolysis in the application of drug delivery in the presence of microbubbles. To achieve this goal, human red blood cells mixed with microbubbles were exposed to 1-MHz pulsed ultrasound. The hemolysis level was measured by a flow cytometry, and the cavitation dose was detected by a passive cavitation detecting system. The results demonstrate that larger cavitation dose would be generated with the increase of acoustic pressure, which might give rise to the enhancement of hemolysis. Besides the experimental observations, the acoustic pressure dependence of the radial oscillation of microbubble was theoretically estimated. The comparison between the experimental and calculation results indicates that the hemolysis should be highly correlated to the acoustic cavitation.
目的 评价32通道线圈高并行采集加速3.0 T MR对比增强全心冠状动脉成像（CECMRA）技术的临床应用价值.方法 对拟诊冠心病的60例患者进行32通道线圈3.0 T CE CMRA检查,成像采用心电门控、呼吸导航、扰相位梯度回波序列,加用非选择性反转回波抑制心肌信号,TT为200 ms.以全心覆盖和并行采集方式获取图像数据.增强扫描采用钆贝葡胺（Gd-BOPTA,0.15 mmoL/kg）慢速静脉注射（0.3 ml/s）.以X线冠状动脉造影结果作为参考标准,采用四格表χ2检验,评价CE CMRA诊断冠状动脉≥50%狭窄的诊断准确性.结果 60例患者中56例成功完成3.0 T CE CMRA,平均扫描时间为（6.0±1.3）min.CE CMRA在28例患者正确检出至少1个有意义狭窄,其诊断敏感性为93.3%.在26例CAG除外冠心病的患者中,CMRA正确排除了23例,其诊断特异性为88.5%.结论 应用32通道相控阵线圈行高并行采集加速3.0 T CE CMRA检查,可以在减少对比剂用量的同时缩短扫描时间,提高诊断准确性.
