Chérin Emmanuel, Brown Jeremy, Måsøy Svein-Erik, Shariff Hamid, Karshafian Raffi, Williams Ross, Burns Peter N, Foster F Stuart
Sunnybrook Health Sciences Centre, Toronto, Ontario, Canada.
Ultrasound Med Biol. 2008 Jun;34(6):949-62. doi: 10.1016/j.ultrasmedbio.2007.11.017. Epub 2008 Feb 21.
In this paper, radial modulation imaging of microbubbles is investigated at high frequency. A modulation pulse frequency of 3.7 MHz with an amplitude ranging from 0 to 250 kPa, and a 1.3-MPa 20-MHz broadband imaging pulse were used. Radial modulation effects were observed on a population of flowing microbubbles and quantified using a Doppler-type processing technique. Artifact signals related to the generation of harmonics by bubbles strongly resonating at the modulation frequency were observed. The bubble response to simultaneous modulation and imaging excitations was simulated for different combinations of bubble sizes and modulation amplitudes. Simulation results confirm the hypothesis that the generation of harmonics of the modulation frequency can be detected by the imaging transducer. Simulations indicate that the modulation frequency should be chosen lower than the resonant frequency of the biggest bubbles present in the population. The simulation also suggests that a 10% variation of bubble diameter induced by the modulation excitation is sufficient for radial modulation imaging. In conclusion, the effects of radial modulation are detectable at a high frequency. Therefore, radial modulation imaging has potential for high-resolution imaging of microbubbles in the microvasculature.
本文研究了高频下微泡的径向调制成像。使用了调制脉冲频率为3.7MHz、幅度范围为0至250kPa的信号，以及一个1.3MPa、20MHz的宽带成像脉冲。在一群流动的微泡上观察到了径向调制效应，并使用多普勒型处理技术进行了量化。观察到了与在调制频率下强烈共振的气泡产生谐波相关的伪像信号。针对不同气泡尺寸和调制幅度的组合，模拟了气泡对同时调制和成像激励的响应。模拟结果证实了成像换能器能够检测到调制频率谐波产生的假设。模拟表明，调制频率应选择低于群体中存在的最大气泡的共振频率。模拟还表明，由调制激励引起的气泡直径10%的变化足以进行径向调制成像。总之，径向调制效应在高频下是可检测的。因此，径向调制成像在微血管中微泡的高分辨率成像方面具有潜力。
