【摘要】 高频剪切波对粘性参数的准确估计非常重要。为了提高高频剪切波的检测能力,并研究其对粘弹性参数估计的影响,本研究探讨了基于正交频率脉冲激励的超声振动计方法。通过构造具有特定频谱特性的正交频率波形,经稀疏采样之后激励组织振动,可以增强剪切波的高频分量。以新鲜猪肝为对象进行离体实验。选择二进制编码和两种正交频率编码脉冲激励组织振动,然后分别运用激光振动计和超声对不同编码激励方式产生的剪切波进行检测。激光振动计实验证明了该方法可以有效增强剪切波的高频分量,而从超声实验结果上看,与二进制编码激励方式的结果相比,当只用100~400 Hz剪切波速度拟合求解时,三码片与六码片的正交频率脉冲激励所估计得到的剪切弹性和剪切粘性的相对偏差分别为2.3%和4.1%,13.6%和11.5%;而当将所有频率剪切波速度用于拟合求解时,三码片与六码片的正交频率脉冲激励所估计得到的剪切弹性和剪切粘性的相对偏差分别为10.6%和3.5%,5.4%和11.8%。实验结果表明,正交频率编码激励方式可以降低激励峰值声强,并提高系统对高频剪切波的检测能力;另一方面,高频剪切波对粘弹性估计值具有影响,但其影响方式还不确定,需要进一步研究。更多还原

【Abstract】 The high frequency shear wave is very important for accurately estimating values of viscosity. To improve the detecting ability of high frequency shear wave and investigate its impact on the estimation of viscoelastic parameters,a method based on orthogonal frequency pulse excitation for ultrasound vibrometry was introduced in this paper. In this method,an orthogonal frequency wave with preferred spectrum distribution was designed and sampled sparsely and used to induce tissue vibration,which can enhance the energy of higherharmonic of induced shear wave. Fresh swine liver was used in experiments in vitro. Binary pulse and two orthogonal frequency pulses were chosen for inducing tissue vibration and the shear waves induced by different excitation pulses were detected by using laser vibrometry and ultrasound technique. Laser vibrometry experiment demonstrates that this method can enhance effectively the high frequency component of induced shear wave. As can be seen from the result of the ultrasound experiment,comparing with the results of binary pulse excitation,the relative bias of estimation of shear elasticity and shear viscosity were 2. 3% and 4. 1%,13. 6% and 11. 5%for three-chip and six-chip orthogonal pulse excitation respectively when using velocity of frequency of 100 to400 Hz for fitting calculation. The relative bias of the shear elasticity estimation and shear viscosity were10. 6% and 3. 5%,5. 4% and 11. 8% for three-chip and six-chip orthogonal pulse excitation respectively when using velocity of all frequency for fitting calculation. Experimental results suggest that orthogonal frequency pulse excitation can reduce the peak ultrasound intensity and enhance the detecting ability of higher harmonic shear wave. On the other hand,the estimated values of viscoelasticity can be impacted by the higher harmonic shear wave,but the ways of how to produce impacts are still unknown and need further study.更多还原