Shi W T, Forsberg F
Department of Radiology and Jefferson Ultrasound Research and Education Institute, Thomas Jefferson University, Philadelphia, PA 19107 USA.
Ultrasound Med Biol. 2000 Jan;26(1):93-104. doi: 10.1016/s0301-5629(99)00117-9.
The nonlinear properties of microbubble contrast agents have been used to create contrast-specific imaging modalities such as harmonic imaging and subharmonic imaging. Thus, a better understanding of the nonlinear performance of contrast microbubbles may enhance the diagnostic capabilities of medical ultrasound (US) imaging. The first and second harmonic, the 1/2 order subharmonic and the 3/2 order ultraharmonic components in spectra of scattered signals from Optison microbubbles insonified at 2 and 4 MHz have been investigated using an in vitro laboratory pulse-echo system. The development of these signal components over time is quite different for 2-MHz insonification compared to 4-MHz insonification. Scattered subharmonic and ultraharmonic signals are much more time-dependent than first and second harmonic echoes. The dependence of the first and second harmonic, subharmonic and ultraharmonic components on acoustic pressure for 2-MHz insonification is similar to that for 4-MHz insonification. The first and second harmonic components increase linearly with acoustic pressure (in double logarithmic scales) and the subharmonic and ultraharmonic amplitudes undergo rapid growths in the intermediate acoustic pressure range and much slower increases at both lower and higher acoustic pressures.
微泡造影剂的非线性特性已被用于创建特定于造影剂的成像模式，如谐波成像和次谐波成像。因此，更好地了解造影微泡的非线性性能可能会提高医学超声（US）成像的诊断能力。使用体外实验室脉冲回波系统研究了在2和4 MHz频率下对Optison微泡进行超声照射时，散射信号频谱中的一阶和二阶谐波、1/2阶次谐波和3/2阶超谐波分量。与4 MHz超声照射相比，2 MHz超声照射时这些信号分量随时间的变化有很大不同。散射的次谐波和超谐波信号比一阶和二阶谐波回波更依赖于时间。2 MHz超声照射时一阶和二阶谐波、次谐波和超谐波分量对声压的依赖性与4 MHz超声照射时相似。一阶和二阶谐波分量随声压呈线性增加（在双对数尺度下），次谐波和超谐波幅度在中等声压范围内快速增长，在较低和较高声压下增长则慢得多。
