Quantitative Assessment of Viscoelasticity of Soft Tissue Based on Orthogonal Frequency Pulse Excitation#br#
1 Department of Biomedical Engineering, School of Biomedical Engineering and Instrument Science, Zhejiang University, Hangzhou 310029, China
2 Department of Biomedical Engineering, School of Medicine, Shenzhen University, Shenzhen 518060, China
3 Nationalregional Key Technology Engineering Laboratory for Medical Ultrasound, Shenzhen 518060, China
4 Guangdong Key Laboratory for Biomedical Measurement and Ultrasound Imaging, Shenzhen 518060, China
5 Department of Electrical and Computer Engineering, St. Cloud State University, St. Cloud, MN 56301, USA
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 higher harmonic 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 threechip and sixchip orthogonal pulse excitation respectively when using velocity of frequency of 100 to 400 Hz for fitting calculation. The relative bias of the shear elasticity estimation and shear viscosity were 10.6% and 3.5%，5.4% and 11.8% for threechip and sixchip 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.
林浩铭1郑翊5陈昕2，3，4刘盼盼2，3，4郭燕荣1，. 基于正交频率脉冲编码激励的软组织粘弹性定量测量[J]. 中国生物医学工程学报, 2014, 33(4): 392-401.
LIN Hao Ming1 ZHENG Yi5CHEN Xin2,3,4LIU Pan Pan2,3,4GUO Yan Rong2,3,4WANG Tian Fu 2,3,4CHEN Si Ping1,2,3,4. Quantitative Assessment of Viscoelasticity of Soft Tissue Based on Orthogonal Frequency Pulse Excitation#br# . journal1, 2014, 33(4): 392-401.
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