Mamou Jonathan, Ketterling Jeffrey A
Frederic L. Lizzi Center for Biomedical Engineering, Riverside Research Institute, New York, New York 10038, USA.
J Acoust Soc Am. 2009 Jun;125(6):4078-91. doi: 10.1121/1.3117384.
Ultrasound contrast agents (UCAs) are designed to be used below 10 MHz, but interest is growing in studying the response of agents to high-frequency ultrasound. In this study, the subharmonic response of polymer-shelled UCAs with a mean diameter of 1.1 mum excited with 40-MHz tone-bursts of 1-20 cycles was analyzed. UCAs were diluted in water and streamed through a flow phantom that permitted single-bubble backscatter events to be acquired at peak-negative pressures from 0.75 to 5.0 MPa. At each exposure condition, 1000 single-bubble-backscatter events were digitized. Subharmonic content at 20 MHz was screened using a conventional and a singular-value-decomposition (SVD) method. The conventional method evaluated each event spectrum individually while the SVD method treated the 1000-event data set at one time. A subharmonic score (SHS) indicative of how much subharmonic content a 1000-event data set contained was computed for both methods. Empirical-simulation results indicated that SHSs obtained from the two methods were linearly related. Also, experimental data with both methods indicated that subharmonic likelihood increased with pulse duration and peaked near 2 MPa. The SVD method also yielded quantitative information about subharmonic events not available with the conventional method.
超声造影剂（UCAs）设计用于10MHz以下，但对研究造影剂对高频超声的响应的兴趣日益增加。在本研究中，分析了平均直径为1.1μm的聚合物壳UCAs在1至20个周期的40MHz短脉冲串激发下的次谐波响应。将UCAs稀释于水中，并使其流过一个流动模型，该模型允许在0.75至5.0MPa的峰值负压下采集单气泡后向散射事件。在每个暴露条件下，对1000个单气泡后向散射事件进行数字化处理。使用传统方法和奇异值分解（SVD）方法筛选20MHz处的次谐波含量。传统方法单独评估每个事件频谱，而SVD方法一次性处理1000个事件的数据集。为两种方法计算了一个次谐波分数（SHS），该分数表示一个1000个事件的数据集包含多少的次谐波含量。经验模拟结果表明，从两种方法获得的SHS呈线性相关。此外，两种方法的实验数据均表明，次谐波可能性随脉冲持续时间增加而增加，并在2MPa附近达到峰值。SVD方法还产生了传统方法无法获得的关于次谐波事件的定量信息。
