Engineered microsphere contrast agents for optical coherence tomography

Contrast agents are utilized in virtually every imaging modality to enhance diagnostic capabilities. We introduce a novel class of optical contrast agent, namely, encapsulating microspheres, that are based not on fluorescence but on scattering nanoparticles within the shell or core. The agents are suitable for reflection- or scattering-based techniques such as optical coherence tomography, light microscopy, and reflectance confocal microscopy. We characterize the optical properties of gold-, melanin-, and carbon-shelled contrast agents and demonstrate enhancement of optical coherence tomography imaging after intravenous injection of such an agent into a mouse.     

Terahertz interferometric synthetic aperture tomography for confocal imaging systems

Terahertz (THz) interferometric synthetic aperture tomography (TISAT) for confocal imaging within extended objects is demonstrated by combining attributes of synthetic aperture radar and optical coherence tomography. Algorithms recently devised for interferometric synthetic aperture microscopy are adapted to account for the diffraction-and defocusing-induced spatially varying THz beam width characteristic of narrow depth of focus, high-resolution confocal imaging. A frequency-swept two-dimensional TISAT confocal imaging instrument rapidly achieves in-focus, diffraction-limited resolution over a depth 12 times larger than the instrument's depth of focus in a manner that may be easily extended to three dimensions and greater depths.     

Spatial and temporal coherence effects in interference microscopy and full‐field optical coherence tomography

Low‐coherence optical microscopy or optical coherence microscopy uses light with short coherence length. The well‐known case is: “white‐light interferometry”, which became recently more known as: “optical coherence tomography”. However, when lenses and microscope objectives are used to create interferometric images, in what is known classically as “interference microscopy” or today as “full‐field optical coherence tomography” the spatial coherence starts to play a critical role. In this article the coherence effects in low‐coherence optical microscopy are reviewed. As this technology is becoming increasingly publicized due to its importance in three‐dimensional imaging, particularly of scattering biological media and optical metrology, the understanding of the fundamental physics behind it is essential. The interplay between longitudinal spatial coherence and temporal coherence and the effects associated with them are discussed in detail particularly when high numerical apertures are used. An important conclusion of this study is that a high‐contrast, high‐resolution system for imaging of multilayered samples is the one that uses narrowband illumination and high‐NA objectives with an index‐matching fluid. Such a system, when combined with frequency‐domain operation, can reveal nearly real‐time three‐dimensional images, and is thus competitive with confocal microscopy.     

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.     

Sequential optical coherence tomography and confocal imaging

We report a system capable of sequentially acquiring two en-face images of different depth resolutions. The two images are generated by use of different principles, optical coherence tomography (OCT) and confocal microscopy, and have depth resolutions, at present, of better than 20 microm and over 0.12 mm, respectively. The lower-depth-resolution image is ideal for target positioning before collection of stacks of en-face OCT images. Switching between the two types of image by flipping an opaque screen in the reference arm, coupled with self-adjusting gain operation of avalanche photodiodes in the receiver. We illustrate the usefulness of the system by imaging a leaf and an optic nerve in vivo.     

一种新的生物医学用快速实时低相干显微成象原理

本文讨论了一种将共焦显微术与迈克耳逊干涉术相结合,并利用宽带低相干光源相干长度短的特点而形成的一种可对高密度非透明样品进行显微成象的方法,并将这种显微成象方法与共焦显微成象方法进行了比较,最后讨论了一种快速实时成象的原理,基于这种原理设计的仪器将为生物和医学工作者提供一种新的非侵入测量和诊断手段.     

Speckle variance detection of microvasculature using swept-source optical coherence tomography

We report on imaging of microcirculation by calculating the speckle variance of optical coherence tomography (OCT) structural images acquired using a Fourier domain mode-locked swept-wavelength laser. The algorithm calculates interframe speckle variance in two-dimensional and three-dimensional OCT data sets and shows little dependence to the Doppler angle ranging from 75 degrees to 90 degrees . We demonstrate in vivo detection of blood flow in vessels as small as 25 microm in diameter in a dorsal skinfold window chamber model with direct comparison with intravital fluorescence confocal microscopy. This technique can visualize vessel-size-dependent vascular shutdown and transient vascular occlusion during Visudyne photodynamic therapy and may provide opportunities for studying therapeutic effects of antivascular treatments without on exogenous contrast agent.     

Time-gated Fourier-domain optical coherence tomography

A novel optical coherence tomography (OCT) system is presented that combines Fourier-domain OCT with incoherent nonlinear time gating. By processing backscattered light in the optical domain, the user can select a restricted depth field of view for improved contrast and acquisition speed. This technique has the additional advantage that imaging is done in the infrared (approximately 1280 nm) but is detected in the visible(approximately 504 nm).     

Fiber-optic-bundle-based optical coherence tomography

A fiber-optic-bundle-based optical coherence tomography (OCT) probe method is presented. The experimental results demonstrate this multimode optical fiber-bundle-based OCT system can achieve a lateral resolution of 12 microm and an axial resolution of 10 microm with a superluminescent diode source. This novel OCT imaging approach eliminates any moving parts in the probe and has a primary advantage for use in extremely compact and safe OCT endoscopes for imaging internal organs and great potential to be combined with confocal endoscopic microscopy.     

Near-infrared dyes as contrast-enhancing agents for spectroscopic optical coherence tomography

Optical coherence tomography (OCT) images of biological tissues often have low contrast. Spectroscopic optical coherence tomography (SOCT) methods have been developed to enhance contrast but remain limited because most tissues are not spectrally active in the frequency bands of laser sources commonly used in OCT. Near-infrared (NIR) dyes with absorption spectra features within the OCT source spectrum can be used for enhancing contrast in this situation. We introduce and demonstrate the use of NIR dyes as contrast agents for SOCT. Contrast-enhanced images are compared with fluorescence microscopy, demonstrating a link between SOCT and fluorescence imaging.     

用于频域光学相干层析成像的深度分辨色散补偿方法

提出一种深度分辨的色散补偿方法,用于增强频域光学相干层析成像的纵向分辨率。将频域光学相干层析成像采集的干涉谱信号傅里叶变换到空域,获取对应不同深度的干涉谱条纹相位,通过对其进行调整实现对被测样品不同深度处的色散的精确补偿。避免传统方法中采用统一色散系数进行色散补偿所带来的过补偿与欠补偿误差,可以有效消除色散引起的频域光学相干层析成像系统点扩展函数的展宽和扭曲。模拟和实验结果表明,基于深度分辨的色散补偿方法在样品的全深度探测范围内可以达到较佳的补偿效果,可有效提高光学相干层析成像系统的纵向分辨率。     

生物医学领域中超连续激光光谱技术的研究进展

超连续谱激光指的是当泵浦激光穿过特殊光波导时,一系列的非线性效应引起入射激光束的光谱展宽,从而输出宽光谱激光束。随着超快激光和光子晶体光纤技术的发展,利用超短脉冲在光子晶体光纤中的传播链产生相干的且亮度高的超连续谱激光成为了一种理想的白光源。自从超连续谱激光源投入应用以来,其应用领域越来越广。尤其在生物医学的细胞、血液等样品分析当中,荧光光谱学、流式细胞仪、共焦显微、光学相干层析等技术都是强有力的分析工具,在采用这些先进技术的科学仪器中,超连续谱激光源成为了一种主要光学部件。首先对超连续谱激光源的国际研究进展作了详细介绍,然后对超连续激光光谱技术在显微成像、流式细胞仪、荧光寿命成像显微、荧光共振能量转移、光学相干层析、共焦显微生物医学分析等生物医学领域中的发展及应用作了综合阐述。对超连续激光光谱技术在非接触式血液制品鉴别的需求、方案及研究进展进行了重点论述,包括覆盖400～2 000 nm光谱范围的光纤化轻型超连续谱激光光源研究;采用超连续谱激光光谱方法探索不同物种血液的种属特征;根据大数据的血液样品光谱特征元数据库分析建立数学模型,利用数学模型实现对血液样品种属光谱学判定;血液鉴别光谱分析便携式整机系统研发等。对超连续激光光谱技术在生物医学领域的应用前景作了展望。     

Linear optical coherence tomography system with a downconverted fringe pattern

Linear optical coherence tomography (LOCT) systems are a simple and robust alternative to time-domain optical coherence tomography systems, but a detector with approximately 10(4) pixels is needed for an imaging depth of 2 mm. We present a new system for LOCT with a special mask attached to the image sensor. The mask essentially performs a downconversion of the spatial frequencies by multiplication with a second spatial frequency. This reduces the fringe frequency of the optical coherence tomography signal so that the signal can be sampled with fewer pixels.     

Micromachined array tip for multifocus fiber-based optical coherence tomography

High-resolution optical coherence tomography demands a large detector bandwidth and a high numerical aperture for real-time imaging, which is difficult to achieve over a large imaging depth. To resolve these conflicting requirements we propose a novel multifocus fiber-based optical coherence tomography system with a micromachined array tip. We demonstrate the fabrication of a prototype four-channel tip that maintains a 9-14-microm spot diameter with more than 500 microm of imaging depth. Images of a resolution target and a human tooth were obtained with this tip by use of a four-channel cascaded Michelson fiber-optic interferometer, scanned simultaneously at 8 kHz with geometric power distribution across the four channels.     

Polarization-resolved second-harmonic-generation optical coherence tomography in collagen

We describe a novel imaging technique, second-harmonic-generation optical coherence tomography (SHOCT). This technique combines the spatial resolution and depth penetration of optical coherence tomography (OCT) with the molecular sensitivity of second-harmonic-generation spectroscopy. As a consequence of the coherent detection required for OCT, polarization-resolved images arise naturally. We demonstrate this new technique on a skin sample from the belly of Icelandic salmon, acquiring polarization-resolved SHOCT and OCT images simultaneously.     

Gold nanocages as contrast agents for spectroscopic optical coherence tomography

We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical coherence tomography (OCT). Monodispersed gold nanocages of an approximately 35 nm edge length exhibit strong optical resonance, with the peak wavelength tunable in the near-infrared range. We characterized the optical properties of the nanocage by using OCT experiments along with numerical calculations, revealing an absorption cross section approximately 5 orders of magnitude larger than conventional dyes. Experiments with tissue phantoms demonstrated that the nanocages provide enhanced contrast for spectroscopic as well as conventional intensity-based OCT imaging.     

金纳米星诊疗剂的光热特性及其在光热治疗和光学相干层析成像中的应用研究

为了开发一种优异的用于光热治疗和光学相干层析成像的金纳米星诊疗剂,对金纳米星的制备、光热特性以及光热治疗和光学相干层析成像中的应用进行研究.利用尖端结构增强金纳米材料的局域表面等离子体共振特性,通过种子介导法制备了多枝化的金纳米星,多尖端的结构使其具有明显的光热效果,并探究了其作为光热治疗的诊疗剂和光学相干层析成像造影...     

Numerical correction of coherence gate in full-field swept-source interference microscopy

A big problem in low-coherence interference microscopy is the degradation of the coherence signal caused by shift of the angular and temporal spectrum gates. It limits the depth of field in confocal optical coherence microscopy and degrades images of sample inner structure in most interference microscopy techniques. To overcome this problem we propose numerical correction of the coherence gate in application to full-field swept-source interference microscopy. The proposed technique allows three-dimensional sample imaging without mechanical movement of the microscope components and is also capable of determining separately the geometrical thickness and the refractive index of the sample layers, when the sample contains a transversal pattern. The applicability of the proposed technique is verified with numerical simulation.     

界面折射率不一致对显微成像穿透深度的限制

在运用共焦显微术及低相干显微成像术等进行光学断层成像时,要将光束聚焦到样品内部以便实现光学断层成像,然而由于生物组织等的折射率与盖玻璃以及浸液不同,因而会引入很大的球差,从而使入射电磁波发生畸变.分析了由于多层折射率不一致而引入的球差的大小,并运用所得的公式计算了折射率不一致对光在样品中穿透深度及焦面附近光场分布的影响.     

Spectral-domain optical coherence phase and multiphoton microscopy

We describe simultaneous quantitative phase contrast and multiphoton fluorescence imaging by combined spectral-domain optical coherence phase and multiphoton microscopy. The instrument employs two light sources for efficient optical coherence microscopic and multiphoton imaging and can generate structural and functional images of transparent specimens in the epidirection. Phase contrast imaging exhibits spatial and temporal phase stability in the subnanometer range. We also demonstrate the visualization of actin filaments in a fixed cell specimen, which is confirmed by simultaneous multiphoton fluorescence imaging.