德国慕尼黑工业大学Vasilis Ntziachristos团队研究了光声信号的非线性和一种新的成像对比机制。相关论文于2025年3月27日发表在《光：科学与应用》杂志上。

光声信号在高于几mJ/cm²的光通量下表现为非线性，这可能会影响测量的解释和量化。有人提出，光声非线性是由纳米气泡的热诱导形成或局部热物理参数的变化引起的。然而，这种解释仅在比生物医学光声成像（>20mJ/cm²）中通常使用的通量高得多的情况下或在金纳米粒子等具有高吸收系数的材料存在的情况下有效。

研究组提出，响应于光子吸收的电磁介电常数变化是低通量下光声信号非线性的主要来源。他们提供了支持这一假设的理论和实验证据，并表明由于介电常数变化引起的光声压响应可以解释光声信号的非线性行为，介电常数的变化是热激发三阶非线性磁化率的函数。由于不同材料表现出不同的热激发三阶非线性磁化率，这一特性可以作为一种新的对比机制，可以识别物质介电常数对光子诱导温度变化的敏感性。

因此，研究组提出了一种基于非线性光声信号的成像方法，该方法利用了这种新发现的对比机制。这些发现可能对提高光声学的准确性具有深远的影响，利用提出的新对比机制将促进人们对细胞和组织功能的理解。

附：英文原文

Title: Nonlinearity of optoacoustic signals and a new contrast mechanism for imaging

Author: Malekzadeh-Najafabadi, Jaber, Prakash, Jaya, Razansky, Daniel, Ripoll, Jorge, Gujrati, Vipul, Ntziachristos, Vasilis

Issue&Volume: 2025-03-27

Abstract: Optoacoustic signals behave nonlinearly at light fluences above a few mJ/cm2, which may affect the interpretation and quantification of measurements. It has been proposed that optoacoustic nonlinearity arises from the heat-induced formation of nanobubbles or changes in local thermo-physical parameters. However, such explanations are only valid at much higher fluences than typically used in biomedical optoacoustic imaging (>20 mJ/cm2) or in the presence of materials with high absorption coefficients such as gold nanoparticles. We propose herein that electromagnetic permittivity changes in response to photon absorption are major source of optoacoustic signal nonlinearity at low fluences. We provide theoretical and experimental evidence that supports this postulation and show that optoacoustic pressure responses due to permittivity changes, which are function of thermally excited third-order nonlinear susceptibility, can explain the nonlinear behavior of the optoacoustic signal. Since different materials exhibit different thermally excited third-order nonlinear susceptibility, this property could function as a new contrast mechanism that can identify the sensitivity of a substance’s dielectric constant to photon-induced temperature changes. Consequently, we propose an imaging method based on nonlinear optoacoustic signals that exploits this newly identified contrast mechanism. These findings may have far-reaching implications for improving the accuracy of optoacoustics and utilizing the proposed new contrast mechanism would advance our understanding of cellular and tissue functionality.

DOI: 10.1038/s41377-025-01772-7

Source: https://www.nature.com/articles/s41377-025-01772-7