光声层析成像的信号处理

报道了采用滤波反投影的光声层析成像的信号处理方法，为了还原空间位置的光声信号，声探测器接收到的光声信号和探测器的脉冲响应在频域进行逆卷积处理；由于光声信号相对于触发时刻的延迟时间就是光声源到探测器的走时，重建时根据光声信号的延迟时间以及声速的距离，把速度势信号反投影到与探测器等距离的圆弧上。通过多个角度的反投影，能够重建出光声源的图像，但是由于反投影时光声信号投影到没有光声源的地方产生伪迹信号，模糊了光声源图像的边界，降低了图像的分辨率和对比度。因此在反投影之前采用CT成像中的R-T空间滤波函数与光声速度势信号进行卷积处理，然后再进行反投影成像；这种方法降低了由反投影带来的伪迹。应用这些处理方法，获得了埋藏深度为12mm的四个光吸收体的二维光声层析成像。     

声折射对光声成像的影响

研究了光声信号声速失配时所起的声折射对光声成像的影响,提出了利用与组织声速匹配的耦合液进行光声成像,并配置了几种适合于组织声速的超声耦合液.实验结果表明,进行声速匹配后重建出的图像对比度有明显地提高,背景伪迹减少,分辨率由0.50 mm提高到0.15 mm,重建图像与实物十分吻合.     

光声成像技术在生物医学中的研究进展

简要介绍了生物医学中的光声成像技术机理,总结报道了国内外几种典型的光声成像方法和光声图像重建算法的发展历程及其最新进展,指出该技术是一种很有应用前景的医学检测方法。     

频率域光声成像系统的研究

频率域光声成像是指使用连续波激光器输出激光光源,利用该调制后的激光信号辐射组织,在频率域对激励的光声信号进行处理并成像的方式。首先阐述光声成像和频率域光声成像的原理、发展以及研究现状,然后介绍频率域光声成像的具体实验方法和基本重建算法。为了弥补时域光声成像成本高、伤害性大、便携性差等缺点,提出了频率域光声成像的两种成像方式,给出了完整的实验系统结构图,展示其相对于传统时域光声成像不同的研究特点与方向。最后对频率域光声成像进行展望,为光声成像在国内的研究和发展提供一定的借鉴和引导。     

多组分固体粉末的光声检测

为了快速无损地鉴别物质的成分,提高光声光谱(PAS)检测多组分固体粉末物的能力,对光声光谱固体颗粒物检测系统和光声信号提取分析方法进行了研究。根据R-G理论,优化设计了基于传声器的非共振圆形光声池。组建了由大功率氙灯、斩波器、锁相放大器、光栅单色仪、数据采集系统和光声池等主要部件构成的系统。采用高灵敏度的声探测器和透过率高的光窗,使用低噪声高信噪比(SNR)放大电路,增强光声信号的强度。实验证实,检测系统性能稳定可靠。采用小波分析提高光声信号分析能力。将硝基化合物粉末和硫酸铜粉末混合物光声信号与两种物质各自的光声信号分析对比,方便准确快速地判断两种物质的存在,为物质鉴别提供依据。     

光声技术在脑组织成像中的应用（特邀）

基于激光诱导超声机制的光声成像技术结合了光学成像的高对比度和超声成像的深穿透性,能无标记、非侵入反映生命体内源性吸收物质的分布,适合啮齿类动物模型全脑的即时成像。为了证明光声技术在脑科学研究和脑疾病监测中的应用,搭建了光声显微成像系统,其空间分辨率可达几十微米,有效成像深度可达1 mm以上,并以APP/PS1转基因阿尔茨海默症（Alzheimer’s disease, AD）模型小鼠和野生型WT小鼠为研究对象,从脑组织切片、离体全脑和活体全脑三个层面探究了光声成像在表征AD鼠和WT鼠脑结构变化和血管网络的能力,证明了光声技术在研究脑疾病发展过程中监控脑结构变化和脑血管网络特征的巨大潜力,可以为诸多脑科学研究和神经退行性疾病发展机制提供更深入的见解。     

基于虚拟仪器的光声信号采集和成像系统

为了实现光声信号的快速采集和图像重建,采用基于虚拟仪器的光声信号采集和成像系统进行光声信号采集,由LABVIEW调用MATLAB程序对采集到的数据进行处理,最后利用滤波反投影重建算法,实现了对模拟组织样品的光声层析成像。成像系统的分辨率为0.15mm,重建图像与实物十分吻合。结果表明,该系统具有快速、方便、直观等特点,有望发展成为一种低成本的实用的临床诊断仪器。     

基于Labview的光声信号采集和成像系统

为了实现光声信号的快速采集和图像重建,采用基于Labview软件平台的光声信号采集和成像系统进行光声信号采集,并调用Matlab程序对采集到的数据进行处理,最后利用滤波反投影重建算法,实现了对模拟组织样品的光声层析成像。成像系统的分辨率为0.15mm,重建图像与实物十分吻合。实验表明,该系统具有快速、方便、直观等特点,有望发展成为一种低成本的实用的临床诊断仪器。     

多波长光声信号的时域与频域比较

为了分析在不同激发波长下不同组织/目标光声信号的时域与频域特点和差异,根据光声信号产生的基本原理,采用光声信号时域和频域分析方法,设计了石墨仿体和离体组织等不同样品的多光谱光声实验。结果表明,样品的光声信号在时域与频域所展示的性能有很大的不同,不同样品的光声信号的声谱是不同的,且在不同激发波长下的声谱的峰值所对应的频率均相同,因而可以用于组织特性的描述、组分识别等用途。此研究有助于利用光声成像实现组织识别,并为进一步利用频谱分析方法研究多光谱光声成像奠定了基础。     

微观探索的新光芒：便携式光声显微成像技术（特邀）

光声成像（PAI）是一种结合了光学成像高对比度和超声成像深穿透性的生物医学成像模态,近年来得到了迅速发展。其中,光声显微成像（PAM）作为光声成像的重要实现方式之一,可以在毫米级的成像深度上实现微米级甚至百纳米级的分辨率,能够实现对生物组织结构、功能和分子的高分辨率成像,已在临床诊断、皮肤病检测和眼科等领域得到广泛应用。首先对PAM的工作原理和实现方式等进行基本介绍,之后围绕便携式PAM技术,从手持与半手持式、脑部可穿戴式及集成多模态3方面对其研究进展进行综述,随后探讨便携式PAM技术面临的挑战,最后进行总结与展望。     

长焦区光声成像系统中的信号补偿

信号衰减问题在许多领域都备受关注,在光声成像系统中各种原因引起的信号衰减同样在很大程度上影响了系统的成像质量以及成像深度。从组织光学、声传输与接收等方面讨论了长焦区光声成像系统中引起信号衰减的因素及其特点,并在此基础上提出相应的补偿策略。补偿策略考虑到光声形成与传输过程中的光衰减与声衰减两方面因素对光声信号的影响,实现了从光与声两方面对检测信号综合补偿。信号补偿实验分别从模拟样品补偿成像与离体甲状腺成像展开。实验结果表明,补偿策略能够较好地对光声信号进行补偿,从而提高了系统的成像深度及成像质量。     

Self‐Assembly of Semiconducting Polymer Amphiphiles for In Vivo Photoacoustic Imaging

Despite the advantages of semiconducting polymer nanoparticles (SPNs) over other inorganic nanoparticles for photoacoustic (PA) imaging, their synthetic method is generally limited to nanoprecipitation, which is likely to cause the issue of nanoparticle dissociation. The synthesis of near‐infrared (NIR) absorbing semiconducting polymer amphiphiles (SPAs) that can spontaneously self‐assemble into homogeneous nanoparticles for in vivo PA imaging is reported. As compared with their counterpart nanoparticles (SPN1) prepared through nanoprecipitation, SPAs generally have higher fluorescence quantum yields but similar size and PA brightness, making them superior over SPN1. Optical and simulation studies reveal that the poly(ethylene glycol) (PEG) grafting density plays a critical role in determining the packing of SP segments inside the core of nanoparticles, consequently affecting the optical properties. The small size and structurally stable nanostructure, in conjunction with a dense PEG shell, allow SPAs to passively target tumors of living mice after systemic administration, permitting both PA and fluorescence imaging of the tumors at signals that are ≈1.5‐fold higher than that of liver. This study thus not only provides the first generation of amphiphilic optically active polymers for PA imaging, but also highlights the molecular guidelines for the development of organic NIR imaging nanomaterials.     

Thermoresponsive Semiconducting Polymer Nanoparticles for Contrast‐Enhanced Photoacoustic Imaging

Photoacoustic (PA) agents with biomarker‐activated signals are developed to enhance the signal‐to‐background ratios (SBRs) for in vivo imaging; however, their SBRs still heavily rely on the concentration difference of biomarkers between diseased and normal tissues. By contrast, external stimuli can provide a remote way to noninvasively control the signal generation from the PA agents and in turn enhance SBR, which are less exploited. This study reports the development of thermoresponsive semiconducting polymer brush with poly(N,N‐dimethylacrylamide)‐r‐(hydroxypropyl acrylate) (PDMA‐r‐HPA) grafts for contrast‐enhanced in vivo imaging. Such a polymer is amphiphilic and can self‐assemble into the nanoparticle (termed as SPNph1) in an aqueous medium, and has lower critical solution temperatures (LCSTs) at 48 °C. Thus, SPNph1 not only has higher photothermal conversion efficiency than the control polymer without PDMA‐r‐HPA grafts, but also can undergo phase separation to form large nanoparticles, leading to enhanced PA signals above LCST. The thermoresponsive PA property of SPNph1 enables in situ remote manipulation of PA signals by photoirradiation to further enhance the tumor SBR. Thus, this study introduces a new generation of organic PA agents with thermoresponsive signal for high‐contrast in vivo imaging.     

Stimuli-Responsive Organic Near-Infrared Photoacoustic Probes

Photoacoustic (PA) imaging is an emerging biomedical imaging technique with the features of non-invasiveness and non-ionization. It takes advantage of the photothermal effect of PA probes to convert absorbed photon energy into heat and subsequent transient thermoelastic tissue expansion for ultrasonic waves for PA images. Thus, PA imaging exhibits the combined superiority of high-contrast optical imaging and deep tissue penetration of acoustic imaging, which furnishes high-resolution and high-contrast tissue images. Stimuli-responsive organic PA agents in the near-infrared (NIR) biological window have attracted increasing attention because of their low biological toxicity and response characteristics. This review focuses on the recent research progress of stimuli-responsive organic NIR probes for PA imaging, including the temperature response, pH response, redox response, metal ion response, and enzyme response. And the stimuli-responsive mechanisms are highlighted in detail. Moreover, their perspectives and challenges are discussed. It will be of great help for the further development of organic NIR PA probes with stimuli-response.     

生物组织的光声成像技术及其在生物医学中的应用

简要介绍了光声成像技术的基本原理,采集系统和成像算法.重点阐述了光声成像技术在肿瘤的早期检测和疗效监测,脑成像和脑功能监测以及临床血管监测等生物医学领域的应用.对光声成像技术应用前景进行了展望.     

Photoacoustic Imaging of Embryonic Stem Cell‐Derived Cardiomyocytes in Living Hearts with Ultrasensitive Semiconducting Polymer Nanoparticles

Human embryonic stem cell‐derived cardiomyocytes (hESC‐CMs) have become promising tools to repair injured hearts. To achieve optimal outcomes, advanced molecular imaging methods are essential to accurately track these transplanted cells in the heart. In this study, it is demonstrated for the first time that a class of photoacoustic nanoparticles (PANPs) incorporating semiconducting polymers (SPs) as contrast agents can be used in the photoacoustic imaging (PAI) of transplanted hESC‐CMs in living mouse hearts. This is achieved by virtue of two benefits of PANPs. First, strong photoacoustic (PA) signals and specific spectral features of SPs allow PAI to sensitively detect and distinguish a small number of PANP‐labeled cells (2000) from background tissues. Second, the PANPs show a high efficiency for hESC‐CM labeling without adverse effects on cell structure, function, and gene expression. Assisted by ultrasound imaging, the delivery and engraftment of hESC‐CMs in living mouse hearts can be assessed by PANP‐based PAI with high spatial resolution (≈100 µm). In summary, this study explores and validates a novel application of SPs as a PA contrast agent to track labeled cells with high sensitivity and accuracy in vivo, highlighting the advantages of integrating PAI and PANPs to advance cardiac regenerative therapies.     

基于智能手机平台的计算光学显微成像技术研究综述

计算光学显微成像技术将光学编码和计算解码相结合,通过光学操作和图像算法重建来恢复微观物体的多维信息,为显微成像技术突破传统成像能力提供了强大的助力。这项技术的发展得益于现代光学系统、图像传感器以及高性能数据处理设备的优化,同时也被先进的通信技术和设备的发展所赋能。智能手机平台作为高度集成化的电子设备,具有先进的图像传感器和高性能的处理器,可以采集光学系统的图像并运行图像处理算法,为计算光学显微成像技术的实现创造了全新的方式。进一步地,作为可移动通信终端,智能手机平台开放的操作系统和多样的无线网络接入方法,赋予了显微镜灵活智能化操控能力与丰富的显示和处理分析功能,可用于实现各种复杂环境下多样化的生物学检测应用。文中从四个方面综述了基于智能手机平台的计算光学显微成像技术,首先综述了智能手机平台作为光学成像器件的新型显微成像光路设计,接下来介绍了基于智能手机平台先进传感器的计算光学高通量显微成像技术,然后介绍了智能手机平台的数据处理能力和互联能力在计算显微成像中的应用,最后讨论了这项技术现存在的一些问题及解决方向。