Microwave-induced thermoacoustic imaging (MTI) has the advantages of high resolution, high contrast, non-ionization, and non-invasive. Recently, MTI was used in the field of breast cancer screening. In this paper, based on the finite element method (FEM) and COMSOL Multiphysics software, a three-dimensional breast cancer model suitable for exploring the MTI process is proposed to investigate the influence of Young’s modulus (YM) of breast cancer tissue on MTI. It is found that the process of electromagnetic heating and initial pressure generation of the entire breast tissue is earlier in time than the thermal expansion process. Besides, compared with normal breast tissue, tumor tissue has a greater temperature rise, displacement, and pressure rise. In particular, YM of the tumor is related to the speed of thermal expansion. In particular, the larger the YM of the tumor is, the higher the heating and contraction frequency is, and the greater the maximum pressure is. Different Young’s moduli correspond to different thermoacoustic signal spectra. In MTI, this study can be used to judge different degrees of breast cancer based on elastic imaging. In addition, this study is helpful in exploring the possibility of microwave-induced thermoacoustic elastic imaging (MTAE).

As an emerging hybrid imaging modality, microwave-induced thermoacoustic imaging (MTAI), using microwaves as the excitation source and ultrasonic signals as the information carrier for combining the characteristics of high contrast of electromagnetic imaging and high resolution of ultrasound imaging, has shown broad prospects in biomedical and clinical applications. The imaging contrast depends on the microwave-absorption coefficient of the endogenous imaged tissue and the injected MTAI contrast agents. With systemically introduced functional nanoparticles, MTAI contrast and sensitivity can be further improved, and enables visualization of biological processes in vivo. In recent years, functional nanoparticles for MTAI have been developed to improve the performance and application range of MTAI in biomedical applications. This paper reviews the recent progress of functional nanoparticles for MTAI and their biomedical applications. The challenges and future directions of microwave thermoacoustic imaging with functional nanoparticles in the field of translational medicine are discussed.As an emerging hybrid imaging modality, microwave-induced thermoacoustic imaging (MTAI), using microwaves as the excitation source and ultrasonic signals as the information carrier for combining the characteristics of high contrast of electromagnetic imaging and high resolution of ultrasound imaging, has shown broad prospects in biomedical and clinical applications. The imaging contrast depends on the microwave-absorption coefficient of the endogenous imaged tissue and the injected MTAI contrast agents. With systemically introduced functional nanoparticles, MTAI contrast and sensitivity can be further improved, and enables visualization of biological processes in vivo. In recent years, functional nanoparticles for MTAI have been developed to improve the performance and application range of MTAI in biomedical applications. This paper reviews the recent progress of functional nanoparticles for MTAI and their biomedical applications. The challenges and future directions of microwave thermoacoustic imaging with functional nanoparticles in the field of translational medicine are discussed.

Microwave-induced thermoacoustic imaging (MTAI) has emerged as a potential biomedical imaging modality with over 20-year growth. MTAI typically employs pulsed microwave as the pumping source, and detects the microwave-induced ultrasound wave via acoustic transducers. Therefore, it features high acoustic resolution, rich electromagnetic contrast, and large imaging depth. Benefiting from these unique advantages, MTAI has been extensively applied to various fields including pathology, biology, material and medicine. Till now, MTAI has been deployed for a wide range of biomedical applications, including cancer diagnosis, joint evaluation, brain investigation and endoscopy. This paper provides a comprehensive review on (1) essential physics (endogenous/exogenous contrast mechanisms, penetration depth and resolution), (2) hardware configurations and software implementations (excitation source, antenna, ultrasound detector and image recovery algorithm), (3) animal studies and clinical applications, and (4) future directions.

Thermoacoustic imaging (TAI) is an emerging high-resolution and high-contrast imaging technology. In recent years, metal wires have been used in TAI experiments to quantitatively evaluate the spatial resolution of different systems. However, there is still a lack of analysis of the response characteristics and principles of metal wires in TAI. Through theoretical and simulation analyses, this paper proposes that the response of metal (copper) wires during TAI is equivalent to the response of antennas. More critically, the response of the copper wire is equivalent to the response of a half-wave dipole antenna. When its length is close to half the wavelength of the incident electromagnetic wave, it obtains the best response. In simulation, when the microwave excitation frequencies are 1.3 GHz, 3.0 GHz, and 5.3 GHz, and the lengths of copper wires are separately set to 11 cm, 5 cm, and 2.5 cm, the maximum SAR distribution and energy coupling e±ciency are obtained. This result is connected with the best response of half-wave dipole antennas with lengths of 11 cm, 4.77 cm, and 2.7 cm under the theoretical design, respectively. Regarding the further application, TAI can be used to conduct guided minimally invasive surgery on surgical instrument imaging. Thus, this paper indicated that results can also guide the design of metal surgical instruments utilized in different microwave frequencies.

Microwave-induced thermoacoustic imaging (MI-TAI) remains one of the focus of attention among biomedical imaging modalities over the last decade. However, the transmission and distribution of microwave inside bio-tissues are complicated, thus result in severe artifacts. In this study, to reveal the underlying mechanisms of artifacts, we deeply investigate the distribution of specific absorption rate (SAR) inside tissue-mimicking phantoms with varied morphological features using both mathematical simulations and corresponding experiments. Our simulated results, which are confirmed by the associated experimental results, show that the SAR distribution highly depends on the geometries of the imaging targets and the polarizing features of the microwave. In addition, we propose the potential mechanisms including Mie-scattering, Fabry- Perot-feature, small curvature effect to interpret the diffraction effect in different scenarios, which may provide basic guidance to predict and distinguish the artifacts for TAI in both fundamental and clinical studies.

针对临床上由质子热声信号脉宽和信噪比的不确定性引起的走时提取困难问题, 提出了一种基于密集网络的走时提取算法。该算法使用密集块代替传统卷积块, 融合了具有不同感受野的特征, 并引入了深度监督和网络剪枝机制, 利用标记好的质子束热声信号数据进行学习, 以提取所需的走时信息。实验结果表明, 相比其他算法, 该算法对质子热声信号走时的提取具有较高的准确率和鲁棒性, 同时展现了实时提取的可行性。

为了研究不同石墨烯发声器结构对热声效率的影响, 建立了石墨烯发声器的声压解析模型, 对单层石墨烯发声器、多层石墨烯发声器以及镍铬基的泡沫石墨烯发声器的发声效率进行了理论与实验研究。首先, 介绍了石墨烯发声器的工作原理, 建立了石墨烯发声器的周期性温度变化模型和声压解析模型。然后, 实验研究了单层石墨烯发声器、多层石墨烯发声器以及镍铬基的泡沫石墨烯发声器的热声效率。实验结果表明: 在14~25 kHz内, 施加6 V交流电, 测距为6 cm的条件下, 单层、多层和泡沫石墨烯发声器的最高SPL分别为35.19, 20.36和33.42 dB, SPL理论值最高约为37.45 dB。具有较低电阻, 较低比热容, 较高导热率的石墨烯发声器可以获得较高的热声效率和声压。

本文提出一种热声、光声双模态乳腺肿瘤检测成像系统。本装置中, 脉冲微波和脉冲激光分别为热声、光声激发源, 产生的热声、光声信号被同一个超声探测器、同一套数据采集装置接收, 用同一种成像算法重建出图像。该系统可同时获取多种互补的诊断参数, 提高检测早期乳腺肿瘤的准确率。