Ultrasonic method of microvibration detection: part II - additional processing method and applications

Abstract Introduction In the last 28 years, the scientific community has been using elastography to evaluate the mechanical properties of biological tissue. The aim of this work was the optimization of the UDmV method, presented in Part I of the series, by means of modifying the technique employed to generate the reference sine and cosine functions, used for phase-quadrature demodulation, and determining how this modification improved the performance of the method. Additionally, the UDmV was employed to characterize the acoustic and mechanical properties of a 7% gelatin phantom. Methods A focused transducer, T F, with a nominal frequency of 2.25 MHz, was used to induce the shear waves, with frequency of 97.644 Hz. Then, the modified UDmV method was used to extract the phase and quadrature components from ultrasonic RF echo-signals collected from four positions along the propagation path of the shear wave, which allowed the investigation of the medium vibration caused by wave propagation. The phase velocity, c s, and attenuation, α s, of the phantom were measured and employed in the calculation of shear modulus, μ, and viscosity, η. Results The computational simulation demonstrated that the modification in UDmV method resulted in more accurate and precise estimates of the initial phases of the reference sinusoidal functions used for phase-quadrature demodulation. The values for c s and μ of 1.31 ± 0.01 m·s-1 and 1.66 ± 0.01 kPa, respectively, are very close to the values found in the literature (1.32 m·s-1 and 1.61 kPa) for the same material. Conclusion The UDmV method allowed estimating of the acoustic and viscoelastic parameters of phantom.

摘要：近28年来，科学界一直采用弹性成像（elastography）技术评估生物组织的力学特性。本研究旨在对本系列第一篇文章中提出的UDmV方法（UDmV method）进行优化：通过修改用于相位正交解调（phase-quadrature demodulation）的参考正弦、余弦函数生成工艺，并探究该优化对该方法性能的提升效果。此外，本研究还采用UDmV方法对7%明胶体模（gelatin phantom）的声学与力学特性进行表征。
方法：本研究使用标称频率为2.25 MHz的聚焦换能器（focused transducer）T_F来激发频率为97.644 Hz的剪切波（shear waves）。随后，采用改进后的UDmV方法，从沿剪切波传播路径四个采集位置获取的超声射频（Radio Frequency, RF）回波信号中提取同相分量与正交分量，以此分析介质受波传播诱导产生的振动。本研究测量了体模的相速度（phase velocity）c_s与衰减系数（attenuation）α_s，并基于这两个参数计算剪切模量（shear modulus）μ及黏度（viscosity）η。
结果：计算模拟结果显示，对UDmV方法的修改使得相位正交解调所用参考正弦函数的初始相位估计更为精准可靠。本研究测得的相速度c_s与剪切模量μ分别为1.31±0.01 m·s⁻¹及1.66±0.01 kPa，与同材料已有文献报道的数值（1.32 m·s⁻¹与1.61 kPa）高度吻合。
结论：UDmV方法可用于估算体模的声学及粘弹性参数。