基于非线性光声的组织热凝固评估技术

Tissue Thermal Coagulation Evaluation Techniques Based on Nonlinear Photoacoustic Techniques

组织的光吸收和通过组织的光通量差异显著影响了当前基于光吸收原理的光声技术对组织热凝固评估的准确性。该研究基于格鲁内森参数的温度依赖性,提出一种消除组织光吸收系数、光通量影响的热凝固评估光声技术。该方法首先通过水浴快速加热组织至41℃,采集不同温度对应的光声信号,基于格鲁内森参数与温度存在的线性关系得到光声信号振幅随组织温度变化的斜率常数。然后利用初始温度对应的光声信号对斜率归一化,即得到一个仅取决于温度依赖性的参数。由于含水量是影响信号温度依赖性的主要因素,而热凝固过程中的组织脱水会导致信号的温度依赖性减弱,因此,可根据归一化斜率减小量来进行组织状态评估。该文采用2种肌肉组织研究温升范围和初始温度对归一化斜率的影响,多次重复试验的结果显示当初始温度小于38℃时,可根据归一化斜率将正常与热凝固后的肌肉组织完全区分开,热凝固后组织的归一化斜率相较于正常组织下降了52.81%~63.47%。试验结果表明所提出的技术具有无损评估组织热凝固的潜力。

The differences in the distribution of light absorption and the light fluence in tissue significantly affect the accuracy of the current light absorption-based photoacoustic techniques for the evaluation of tissue thermal coagulation.In this study,based on the temperature dependence of the Grüneisen parameter,we proposed a thermal coagulation evaluation photoacoustictechnique that eliminates the influence of the inhomogeneous distribution of tissue light absorption coefficient and light fluence.Firstly,the tissue is rapidly heated to 41°C by a water bath,the photoacoustic signals corresponding to different temperatures are acquired,and the slope constant of the photoacoustic signal amplitude with the temperature of the tissue is obtained based on the linear relationship between Grüneisen parameter and temperature.The photoacoustic signal corresponding to the initial temperature is then used to normalize the slope,then a parameter determined only by its temperature dependence is obtained.Since the water content is the main factor affecting the temperature dependence of the signal,tissue dehydration due to the thermal coagulation will weaken the signal's temperature dependence,therefore,the tissue status can be characterized according to the reduction of the normalized slope.In this paper,two kinds of muscle tissues were used to investigate the influence of the ranges of temperature rise and the initial temperature on the normalized slope.The results of the repeated experiments showed that as the initial temperature was less than 38℃,the normal and coagulated muscle tissues could be completely distinguished according to the normalized slope.The normalized slope of the coagulated tissue decreased by 52.81%~63.47%compared to that of the normal tissue.The experimental results indicate the potential of the proposed technique for the non-invasive evaluation of tissue thermal coagulation.