Photoacoustic microscopy

Photoacoustic microscopy (PAM) is a hybrid in vivo imaging technique that acoustically detects optical contrast via the photoacoustic effect. Unlike pure optical microscopic techniques, PAM takes advantage of the weak acoustic scattering in tissue and thus breaks through the optical diffusion limit (∼1 mm in soft tissue). With its excellent scalability, PAM can provide high‐resolution images at desired maximum imaging depths up to a few millimeters. Compared with backscattering‐based confocal microscopy and optical coherence tomography, PAM provides absorption contrast instead of scattering contrast. Furthermore, PAM can image more molecules, endogenous or exogenous, at their absorbing wavelengths than fluorescence‐based methods, such as wide‐field, confocal, and multi‐photon microscopy. Most importantly, PAM can simultaneously image anatomical, functional, molecular, flow dynamic and metabolic contrasts in vivo. Focusing on state‐of‐the‐art developments in PAM, this Review discusses the key features of PAM implementations and their applications in biomedical studies.     

A General Strategy to Encapsulate Semiconducting Polymers within PEGylated Mesoporous Silica Nanoparticles for Optical Imaging and Drug Delivery

Although semiconducting polymers (SPs) have become an important category for optical imaging and phototherapy, their biomedical application is still facing a number of challenges. Herein, a cationic surfactant–assisted approach to encapsulate hydrophobic SPs within highly PEGylated mesoporous silica (mSiO₂) nanoparticles with excellent colloidal stability and enhanced fluorescence in aqueous solution is reported. In comparison to the previously reported amphiphilic polymer coating and silification method, this universal strategy not only suppresses the formation of empty polymer micelles and free silica nanoparticles, but also provides high specific surface area for drug loading. As a proof of concept, furan-containing diketopyrrolopyrrole-based semiconducting polymers (PDFT) are coated with mesoporous silica and utilized for fluorescence imaging in the second near-infrared region (NIR-II, 1000–1700 nm) and drug delivery. In vivo blood vessel imaging and tumor imaging are achieved with high resolution (0.21 mm) and signal-to-background ratio (≈4.2). Additionally, pH-responsive drug release and improved therapeutic effect are observed. By choosing desired SPs, different optical imaging and therapeutic modalities can also be achieved, thus the SP@mSiO₂ nanostructures obtained here provide numerous opportunities for theranostic applications.     

Acoustic radiation force optical coherence elastography for elasticity assessment of soft tissues

Biomechanical properties of soft tissues are important indicators of tissue functions which can be used for clinical diagnosis and disease monitoring. Elastography, incorporating the principles of elasticity measurements into imaging modalities, provides quantitative assessment of elastic properties of biological tissues. Benefiting from high-resolution, noninvasive, and three-dimensional optical coherence tomography, optical coherence elastography (OCE) is an emerging optical imaging modality to characterize and map biomechanical properties of soft tissues. Recently, acoustic radiation force (ARF)–OCE has been developed for elasticity measurements of ocular tissues, detection of vascular lesions, and monitoring of blood coagulation based on remote and noninvasive ARF excitation to both internal and superficial tissues. Here, we describe the advantages of the ARF–OCE technique, the measurement methods in ARF–OCE, the applications in biomedical detection, current challenges, and advances. ARF–OCE technology has the potential to become a powerful tool for in vivo elasticity assessment of biological samples in a noncontact, noninvasive, and high-resolution nature.     

Amplified Photoacoustic Imaging of Tumor through In Situ Cycloaddition

Photoacoustic (PA) imaging has received great attention in the field of biomedical applications due to the combination advantages of the high contrast of optical imaging and the high spatial resolution of ultrasound. The limited targeting property of PA contrast agents is restricted to elaborate its advantage. To overcome this point, a pretargeting strategy is developed to amplify the targeting property and PA imaging of a model dye in vivo. As a proof of concept, the dibenzyl cyclootyne (DBCO)‐modified Fe@Fe₃O₄ nanoparticles (NPs) (Fe@Fe₃O₄/DBCO) and azide‐modified Cy7.5 (Cy7.5‐N₃) are adopted as the pretargeting and PA contrast agents, respectively. Fe@Fe₃O₄/DBCO NPs are first targeted into tumors by the enhanced permeability and retention effect, and then Cy7.5‐N₃ is conjugated to the pretargeted Fe@Fe₃O₄/DBCO labeled tumor cells via strain‐promoted alkyne azide cycloaddition reaction after intravenous injection, which results in an obvious increase of the accumulated dose and PA signal of Cy7.5 in tumor, and simultaneously extends its residence time. This signal amplification strategy should have an important guiding significance for the clinical application in cancer theranostics.     

Super-Resolution Two-Photon Fluorescence Tomography Through the Phase-Shifted Optical Beatings of Bessel Beams for High-Resolution Deeper Tissue 3D Imaging

A novel z-scanning-free epi-detected super-resolution two-photon fluorescence tomography (TPFT) technique enabling super-resolution deeper tissue 3D imaging is reported. To accomplish this, a unique method is conceived by generating the phase-shifted optical beatings of Bessel beams (PS-OB³) with a spatial light modulator (SLM) to break the diffraction limit for enhancing both the lateral and axial resolutions as well as improving the penetration depth in TPFT for super-resolution deeper tissue imaging. By electronically varying the optical beating frequency and the phase shifts of the beating patterns through SLM, the depth-resolved TPF signals about the volumetric tissue are encoded in the spatial frequency domain and hence, a series of depth-resolved TPF images can be retrieved by implementing inverse fast Fourier transform without a need of mechanical depth-scanning. PS-OB³ TPFT provides ≈1.3- and 2-fold improvements in lateral and axial resolutions in comparison with conventional point-scan TPF imaging. It is also illustrated that the epi-detected PS-OB³ TPFT imaging with inherent scattering-resilient properties of the Bessel beams employed gives over 2-fold improvement in imaging depth in porcine brain tissue compared to conventional point-scan Gaussian beam TPF imaging. The z-scanning-free optical sectioning ability of PS-OB³ method developed in TPFT is universal, which can be readily extended to practically any other nonlinear optical imaging modalities for super-resolution deeper 3D imaging in biological and biomedical tissues.     

Cobalt Phosphide Nanoparticles Applied as a Theranostic Agent for Multimodal Imaging and Anticancer Photothermal Therapy

Biocompatible single‐component theranostic nanoagents instinctly affording multiple imaging modalities with satisfying therapeutic functions are highly desirable for anticancer treatments. Although cobalt‐based phosphides are well‐recognized as competent electrocatalysts, their potentials for biomedical applications remain unexplored. In this work, cobalt phosphide nanoparticles (CoP NPs) are developed to be a powerful theranostic agent for multimodal imaging and anticancer photothermal therapy. The uniform CoP NPs in a size of ≈21 nm are synthesized via a facile thermal decomposition method, followed by surface modification. The resultant CoP NPs exhibit excellent compatibility and stability in water as well as various physiological solutions. Supported by the good biocompatibility, strong near‐infrared absorption, and high photothermal conversion property, significant photothermal effect of the NPs is demonstrated, realizing efficient hyperthermia ablation on cancer cells. Importantly, the CoP NPs have shown considerable capabilities on high‐contrast in vitro and in vivo triple‐modal imaging, including infrared thermal (IRT), photoacoustic (PA), and T₂‐weighted magnetic resonance (MR) imaging. This work has unraveled the promising potentials of CoP‐based nanoagent for precise diagnosis and efficient therapy.     

光电技术在生物医学中的应用-现状与发展

简要介绍光电技术在生物医学应用中的发展概况，从基因表达与蛋白质一蛋白质相互作用研究方面，重点讨论了生物分子光子技术的特点与优势，阐明基于分子光学标记的光学成像技术是重要的实时在体监测手段，最后简要讨论了医学光学成像技术在组织功能成像和脑功能成像中的应用原理。     

利用近红外光激发的光声血管造影成像

利用近红外光结合对应波长的光吸收增强对照剂来实现在体小鼠脑皮层血管的光声成像.近红外光在生物组织上有较深的穿透能力;而作为光吸收增强剂的外源染料吲哚菁绿注射到血液系统后则增加了血管对光的选择性吸收,从而增强了血管光声信号的强度.实验在不破坏脑头皮和头盖骨的前提下,通过静脉注射吲哚菁绿,获得小鼠脑皮层血管的光声造影成像.光声重建的血管网络与小鼠脑部解剖照片相当符合.实验结果证明近红外光结合光吸收增强剂的光声血管造影技术对于开展光声脑功能成像,光声分子成像提供了潜在的可行性. 关键词： 光声成像 光吸收增强剂 血管造影 光声信号     

Methodological challenges of optical tweezers‐based X‐ray fluorescence imaging of biological model organisms at synchrotron facilities

Recently, a radically new synchrotron radiation‐based elemental imaging approach for the analysis of biological model organisms and single cells in their natural in vivo state was introduced. The methodology combines optical tweezers (OT) technology for non‐contact laser‐based sample manipulation with synchrotron radiation confocal X‐ray fluorescence (XRF) microimaging for the first time at ESRF‐ID13. The optical manipulation possibilities and limitations of biological model organisms, the OT setup developments for XRF imaging and the confocal XRF‐related challenges are reported. In general, the applicability of the OT‐based setup is extended with the aim of introducing the OT XRF methodology in all research fields where highly sensitive in vivo multi‐elemental analysis is of relevance at the (sub)micrometre spatial resolution level.     

Diode laser based light sources for biomedical applications

Diode lasers are by far the most efficient lasers currently available. With the ever‐continuing improvement in diode laser technology, this type of laser has become increasingly attractive for a wide range of biomedical applications. Compared to the characteristics of competing laser systems, diode lasers simultaneously offer tunability, high‐power emission and compact size at fairly low cost. Therefore, diode lasers are increasingly preferred in important applications, such as photocoagulation, optical coherence tomography, diffuse optical imaging, fluorescence lifetime imaging, and terahertz imaging. This review provides an overview of the latest development of diode laser technology and systems and their use within selected biomedical applications. 670 nm external cavity diode laser for Raman spectroscopy built on a 13 × 4 mm² microbench (Copyright FBH/Schurian.com ).     

X‐ray grating interferometer for biomedical imaging applications at Shanghai Synchrotron Radiation Facility

An X‐ray grating interferometer was installed at the BL13W beamline of Shanghai Synchrotron Radiation Facility (SSRF) for biomedical imaging applications. Compared with imaging results from conventional absorption‐based micro‐computed tomography, this set‐up has shown much better soft tissue imaging capability. In particular, using the set‐up, the carotid artery and the carotid vein in a formalin‐fixed mouse can be visualized in situ without contrast agents, paving the way for future applications in cancer angiography studies. The overall results have demonstrated the broad prospects of the existing set‐up for biomedical imaging applications at SSRF.     

Recent progress in tissue optical clearing

Tissue optical clearing technique provides a prospective solution for the application of advanced optical methods in life sciences. This paper gives a review of recent developments in tissue optical clearing techniques. The physical, molecular and physiological mechanisms of tissue optical clearing are overviewed and discussed. Various methods for enhancing penetration of optical‐clearing agents into tissue, such as physical methods, chemical‐penetration enhancers and combination of physical and chemical methods are introduced. Combining the tissue optical clearing technique with advanced microscopy image or labeling technique, applications for 3D microstructure of whole tissues such as brain and central nervous system with unprecedented resolution are demonstrated. Moreover, the difference in diffusion and/or clearing ability of selected agents in healthy versus pathological tissues can provide a highly sensitive indicator of the tissue health/pathology condition. Finally, recent advances in optical clearing of soft or hard tissue for in vivo imaging and phototherapy are introduced.     

Comparison of Two Tricarbocyanine-Based Dyes for Fluorescence Optical Imaging

Optical technologies are evolving in many biomedical areas including the biomedical imaging disciplines. Regarding the absorption properties of physiological molecules in living tissue, the optical window ranging from 700 to 900 nm allows to use fluorescent dyes for novel diagnostic solutions. Here we investigate the potential of two different carbocyanine-based dyes fluorescent in the near infrared as contrast agents for in vivo imaging of subcutaneously grown tumours in laboratory animals. The primary aim was to modify the physicochemical properties of the previously synthesized dye SIDAG to investigate the effect on the in vivo imaging properties.     

荧光寿命显微成像技术及应用的最新研究进展

由于荧光寿命不受探针浓度、激发光强度和光漂白效应等因素影响,荧光寿命显微成像技术(fluorescence lifetime imaging microscopy, FLIM)在监测微环境变化、反映分子间相互作用方面具有高特异性、高灵敏度、可定量测量等优点,近年来已被广泛应用于生物医学等领域.然而,尽管FLIM的发明和发展已历经数十年时间,其在实际应用中仍然面临着许多挑战.例如,其成像分辨率受衍射极限限制,而其成像速度与成像质量和寿命测量精度则存在相互制约的关系.近几年来,相关硬件和软件的快速发展及其与其他光学技术的结合,极大地推动了FLIM技术及其应用的新发展.本文简要介绍了基于时域和频域的不同寿命探测方法的FLIM技术的基本原理及特点,在此基础上概述了该技术的最新研究进展,包括其成像性能的提升和在生物医学应用中的研究现状,详细阐述了近几年来研究者们通过硬件和软件算法的改进以及与自适应光学、超分辨成像技术等新型光学技术的结合来提升FLIM的成像速度、寿命测量精度、成像质量和空间分辨率等方面所做的努力,以及FLIM在生物医学基础研究、疾病诊断与治疗、纳米材料的生物医学研究等方面的应用,最后对其未来发展趋势进行了展望.     

光声成像研究进展

本文阐述了光声成像的工作原理,光声信号的产生,传播和探测过程,并总结了光声成像的研究进展,包括时域光声成像和频率域光声成像的研究进展、以及各自的特点,为光声成像领域的研究起到一定的借鉴作用。分析认为光声成像技术有着其他医学成像技术没有的诸多优点,如高分辨率、高对比度、成像深度深等具有广阔的应用前景和较高应用价值,是未来生物医学领域最重要的实时医学成像技术之一,因此得到了国际上的广泛关注。     

胶束型磁共振成像分子探针的设计与应用

飞速发展的分子影像学在肿瘤的早期诊断及检测中发挥着越来越重要的作用.磁共振成像(MRI)是分子影像学的重要分支，具有其他成像技术不可比拟的优越性和广阔的发展前景.它不需要放射性示踪剂，没有电离辐射，具有高的空间、时间分辨率和组织对比度.近年来，新型磁共振分子探针及成像序列取得了一系列进展，包括环境响应型分子探针、¹⁹F成像、¹²⁹Xe超极化成像以及化学交换饱和转移成像等，进一步拓展了MRI的应用范围.研究和开发靶向性好、弛豫效率高且安全性好的新型多模态MRI造影剂，进一步提高灵敏度是MRI领域的一项重要课题，例如将胶束的特性与一些MRI新方法结合，寻找合适的胶束体系，以提高MRI分子探针的灵敏度；或者引入多模态分子探针，弥补磁共振方法的不足.本文综述了胶束型MRI分子探针核心技术的研究进展与应用，并指出分子影像技术在生物医学工程研究和临床诊断中的重要性.     

Transillumination Laser Computed Tomography System with Fiber-Optic-Based Coherent Detection Imaging Method - High Spatial-Resolution and Quantitative Tomographic Imaging of Highly Scattering Objects -

We recently proposed and developed a novel transillumination laser computed tomography (CT) imaging system using a fiber-optic method based on coherent detection imaging (CDI) for biomedical use. Use of optical fibers enables portability and robustness against environmental changes in a room, such as variable temperature, air-flow shifts, and unexpected vibrations. In addition, motion-artifact-free images can be obtained because measurements can be performed with the object fixed. In the present paper, we experimentally investigate in detail the fundamental imaging properties of the system, which has a spatial resolution of 500 μm, a dynamic range of approximately 120 dB, and a minimum-detectable-optical power of 10⁻¹⁴W as a result of the excellent properties of the heterodyne detection. Based on experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the transillumination mode, similar to X-ray CT, at sub-millimeter spatial resolution and with quantitativeness. Finally, we demonstrate with experiments using a physical phantom that the imaging system possesses high resolution and quantitative imaging abilities for highly scattering objects.     

Source sparsity based primal-dual interior-point method for three-dimensional bioluminescence tomography

In this paper, an efficient l₁-regularized reconstruction method named the primal-dual interior-point (PDIP) method is presented for three-dimensional bioluminescence tomography (BLT) based on the adaptive finite element framework. Taking into account the sparse characteristic of the bioluminescent source, the BLT inverse problem is considered to be a linear programming problem and is represented by its primal and dual form. The source localization and quantification are obtained by solving the primal-dual Newton equation system. The comparisons between PDIP and the classical conjugate gradient least square (CGLS) algorithm are implemented to validate our method. Results from numerical simulation and an in vivo mouse experiment demonstrate the credibility and the potential of the proposed method in practical BLT reconstruction.     

Analytical study of a flattened Gaussian beam through multi-apertured optical imaging systems of B = 0

By using the methods of the matrix decomposition and expansion of the hard-edged aperture function into a finite sum of complex Gaussian functions, the recurrence propagation expressions for a flattened Gaussian beam (FGB) through multi-apertured optical imaging systems of B = 0 are derived and illustrated with numerical examples. Comparisons with the straightforward numerical integration of the Collins formula and with the previous work are made. It is shown that the main advantages of our methods and results are the more accuracy and great reduction of computer time.     

Impact of molecular tilt angle on the absorption spectra of pentacene:perfluoropentacene blends

We investigate the relation between the optical properties and the average molecular tilt angle for blends of pentacene and perfluoropentacene, which can be considered as a prototypical donor–acceptor complex. Combining near‐edge X‐ray absorption fine‐structure spectroscopy and optical spectroscopy we study thin films of these compounds prepared at three different substrate temperatures T_sub. For T_sub =180 K we observe a larger average tilt angle than for blends prepared at higher substrate temperatures. This orientational change has significant impact on the uniaxial anisotropic optical properties of the mixed films which we measure post growth as well as in real‐time during growth. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)