脂肪组织中异物弹性影响激光超声的数值模拟

Numerical simulation of laser ultrasonics in an adipose tissue affected by the elastic modulus of foreign bodies

生物组织的弹性信息对疾病的诊断具有重要的参考价值.发生了生理性或病理性改变的组织,或组织中生长了异物,常伴随局部弹性参数的较大改变.生物组织的弹性参数对于激光超声信号的产生和传输也有重要影响.本文通过建立热弹机制下脉冲激光照射在含异物脂肪组织中产生和传播超声波的物理模型,采用数值模拟方法,研究了单脉冲激光与含异物脂肪组织相互作用瞬态过程的应力场及其所产生的超声波的传播过程和特性,分析了不同接收点接收到的超声波信号.结果显示,由于脂肪组织和异物的弹性模量参数不同,当激光作用在含异物的脂肪组织上,组织的不均匀性导致产生不同模式的超声波.组织中异物的弹性模量越大,激光超声信号波形的半高宽越窄,而纯脂肪组织激光超声信号波形的半高宽较宽;超声波在较大弹性模量异物中的传播速度较快;含异物脂肪组织的激光超声信号波形有多个界面反射波.此结果可能为进一步研究基于激光超声原理的生物组织无创伤检测方法和技术提供有价值的参考.

The information about elasticity of biological tissues is important in diagnosing disease.The physiological or pathological changes occurring in the biological tissues or a foreign body in the biological tissues are often accompanied by great changes in the elastic parameters.Therefore,the elasticity of the biological tissues can affect the generation and transmission of an ultrasonic signal.Based on the thermoelastic mechanism of a pulsed laser in adipose tissue with foreign bodies,we presented a physical model for ultrasound generation and transmission.The transient responses of the pulsed laser interacting with adipose tissue,the corresponding stress field and the transmission of the related ultrasound were also investigated.Analyzing the laser-induced ultrasonic waveforms in different positions,we found that when the laser acts on the adipose tissue with foreign bodies,the inhomogeneity of the tissue leads to different ultrasound modes.This can be attributed to the difference of the elastic modulus between adipose tissues and foreign bodies.The larger elastic modulus of foreign body in the adipose tissue,the narrower the full width at half maximum of laser ultrasound signal waveform.The latter of a pure adipose tissue is wider than that of the adipose tissue with foreign bodies.The resultant ultrasound spreads more quickly in the foreign bodies with larger elastic modulus.Their laser ultrasound signal waveform has a multiple-interface reflected wave.Our results can promote studies on methods and techniques of ultrasonic noninvasive detection of biological organization.