利用扫描电子声显微镜技术实现定量分层成像(英文)

Quantitatively laminated imaging by scanning electron-acoustic thermal wave microscopy

电子声热波显微镜技术成像过程中,由于不同深度的热源具有不同的相位与幅值,因此产生的声信号的相位与幅值对应于不同的深度和结构.由于热波是高衰减波,所以特别适合于表面层附近结构的检测与分析.实验上利用压电换能器检测声信号,其输出的电信号通过锁相放大器加以放大、并抑制其余不同频率和相位的信号和噪声,因此可以增强特定频率和相位的声信号输出.根据检测到的不同相位的声信号,即可分析样品不同深度的结构,因而扫描电子声热波显微镜技术可以实现分层成像.为了定量估计不同深度的结构对检测到的声信号的贡献,利用热传导方程和热弹方程及其边界条件,可以解得热波在不同深度产生的温度场及声场,因而可求得不同深度的热源产生的声信号的振幅和相位.根据压电方程,可求得不同深度的声源对压电换能器输出电信号的贡献.将理论的计算与实验结果进行拟合,可以定量确定样品的深度剖面结构.本文利用上述成像技术,对大白鼠的肝脏和心脏组织进行分层成像,得到不同深度的分层图像.同时,利用电子声热波检测技术,可测得大白鼠的组织的显微镜样品的热扩散率,其结果为0.45到0.65 mm2/s之间.通过与以前文章报道的猪肝脏组织的显微镜样品测量得到的热扩散率值比较,它们之间的偏离约为7%,由此可知大白鼠的热扩散率测量值是合理的.最后,通过电子声热波成像理论和检测实验结果的比照,对实验的分层成像结果进行数值拟合,可对大白鼠组织进行定量深度分层分析,分层成像深度在一个热波波长范围内,实验中检测深度约为数十微米量级.由此说明,扫描电子声热波显微镜技术可以非破坏性地对不均匀的生物组织和固体材料的表面和亚表面的结构进行三维定量分层成像和表征.

Laminated images of microstructures of biological tissues have been obtained by the scanning electron-acoustic thermal wave microscopy by suitably adjusting the phase,because the acoustic signals produced by the thermal sources at different depths are with different phases.On the other hand,in order to theoretically simulate the laminated imaging by the electron-acoustic microscopy,thermal conduction and thermo-elastic equations are introduced to obtain the distributions of the temperature field and then the acoustic field in the samples.Based on the solutions of the equations and related boundary conditions,the depths of laminated images can be theoretically estimated quantitatively as the thermal diffusivities of the samples are determined.Meanwhile,the thermal diffusivity of the samples can also be measured by the electron-acoustic detection technique.For the biological tissues（heart and liver of rats） the thermal diffusivities are measured,which are in the range of 0.45-0.65 mm2/s,and the measured depths are about several tens micrometers.Therefore,the depth profiling of the biological tissues can be evaluated quantitatively by the theoretical fitting to the experimental laminated images.