基于光声成像的生物组织微结构定征研究进展*

光声成像是一种新兴的复合型生物医学成像技术,它既具有光学成像丰富的光学对比度,又具有声学成像成像深度深、深层组织空间分辨率高的优点。作为一种非侵入式的成像技术,光声成像逐渐显现出极大的生物医学应用潜力。该文首先介绍了光声成像的物理机制,以及光声显微镜和光声计算机断层成像这两种典型的光声成像技术;然后讨论了从光声射频信号中提取组织微结构的尺度、数量密度、弹性等特征参数的研究进展,并展望了其在组织定征和分类上的应用前景。     

生物医学光声成像的研究进展

光声成像是21世纪初发展起来的新兴的生物医学成像技术,它同时具备光学成像和声学成像两者的优点,因而备受关注。本文对生物医学光声成像的发展进行了综述。首先,介绍了光声成像的特点以及相对于广泛应用的光学成像技术和声学成像技术的优点;其次,在成像原理上解释了光声成像优点的成因,并介绍了光声断层成像和光声显微镜这两种典型的光声成像技术;再次,详细介绍了多尺度的光声图像分辨率和成像深度,以及多信息维度的光声成像参数;最后,展望了光声成像在生物医学领域的应用潜力并讨论了其局限性。     

Total variation based gradient descent algorithm for sparse-view photoacoustic image reconstruction

In photoacoustic imaging (PAI), reconstruction from sparse-view sampling data is a remaining challenge in the cases of fast or real-time imaging. In this paper, we present our study on a total variation based gradient descent (TV-GD) algorithm for sparse-view PAI reconstruction. This algorithm involves the total variation (TV) method in compressed sensing (CS) theory. The objective function of the algorithm is modified by adding the TV value of the reconstructed image. With this modification, the reconstructed image could be closer to the real optical energy distribution map. Additionally in the proposed algorithm, the photoacoustic data is processed and the image is updated individually at each detection point. In this way, the calculation with large matrix can be avoided and a more frequent image update can be obtained. Through the numerical simulations, the proposed algorithm is verified and compared with other reconstruction algorithms which have been widely used in PAI. The peak signal-to-noise ratio (PSNR) of the image reconstructed by this algorithm is higher than those by the other algorithms. Additionally, the convergence of the algorithm, the robustness to noise and the tunable parameter are further discussed. The TV-based algorithm is also implemented in the in vitro experiment. The better performance of the proposed method is revealed in the experiments results. From the results, it is seen that the TV-GD algorithm may be a practical and efficient algorithm for sparse-view PAI reconstruction.     

Remote photoacoustic imaging on solid material using a two-wave mixing interferometer

We report on remote and contactless photoacoustic imaging (PAI) for the inspection of solid materials using a two-wave mixing interferometer. In this Letter, a semitransparent sample was excited with picosecond laser pulses. The local absorption of the electromagnetic radiation led to generation of broadband ultrasonic waves inside the sample. Ultrasonic waves arriving at the sample surface were detected utilizing a two-wave mixing interferometer. After data acquisition, the initial pressure distribution was reconstructed using a Fourier space synthetic aperture technique algorithm. We show the potential of PAI for the inspection of semitransparent solid materials.     

Photoacoustic characteristics of lipid-rich plaques under ultra-low temperature and formaldehyde treatment

Photoacoustic imaging(PAI) has been used to characterize the spatial and quantitative features of lipid-rich atherosclerotic plaques with high sensitivity and specificity. In this Letter, we first validate that the ultra-low temperature and formaldehyde treatment have no effect on photoacoustic characteristics of the artery samples.Comparative experiments between the PAI and histological results demonstrate that the ultra-low temperature or formaldehyde treatment has few effects on the PAI of the lipid-rich atherosclerotic plaques; the lipid relative concentration and the lipid percentage by PAI hold high correlation with histology.     

High total variation-based method for sparse-view photoacoustic reconstruction

We propose a novel method by combining the total variation（TV） with the high-degree TV（HDTV） to improve the reconstruction quality of sparse-view sampling photoacoustic imaging（PAI）. A weighing function is adaptively updated in an iterative way to combine the solutions of the TV and HDTV minimizations. The fast iterative shrinkage/thresholding algorithm is implemented to solve both the TV and the HDTV minimizations with better convergence rate. Numerical results demonstrate the superiority and efficiency of the proposed method on sparse-view PAI. In vitro experiments also illustrate that the method can be used in practical sparse-view PAI.     

改进的同步迭代算法在光声血管成像中的应用

光声成像结合了光学成像和声学成像的优点，是一种高分辨率，高对比度的无损伤医学成像技术.一种改进的同步迭代算法应用于光声图像重建.仿真和模拟结果表明，与传统的代数迭代算法相比，在90°，135°，180°的有限场光声成像中，此算法对测量误差的校正和迭代次数的收敛上具有较大的优势，图像重建的速度和成像质量都有了明显的提高.实验中，一种圆形扫描结构的光声成像装置，用于180°的有限场扫描，利用改进的同步迭代算法，重建出了高对比度和高分辨率（60μm）的鸡胚胎光声血管图像.实验证明，这种算法的应用，大幅度减少了数据采集时间，为光声成像技术运用于实时监测血流灌注和肿瘤光动力治疗的血管损伤效应提供了潜在的应用价值. 关键词： 光声成像 有限角度 代数迭代算法 光声血管成像     

Multifocal optical-resolution photoacoustic microscopy in vivo

Although ultrasound arrays have been exploited in photoacoustic imaging to improve imaging speed, ultrasound-array-based optical-resolution photoacoustic microscopy (OR-PAM) has never been achieved previously to our knowledge. Here we present our development of multifocal OR-PAM using a microlens array for optical illumination and an ultrasound array for photoacoustic detection. Our system is capable of imaging hemoglobin concentration and oxygenation in individual microvessels in vivo at high speed. Compared with a single focus, multiple foci reduce the scanning load and increase the imaging speed significantly. The current multifocal system can acquire 1000 × 500 × 200 voxels at ~10 μm lateral resolution within 4 min.     

复谱频域OCT成像的研究

采用频域技术的OCT系统，深度扫描信息由背向散射光谱的傅立叶反变换获得，简化了轴向扫描过程，从而使快速OCT成像成为可能．为了实现复杂生物组织的OCT快速成像，消除谱频域OCT的“混叠”现象、重建样品的真实层析结构，本文引入了相移干涉技术，构建了一套满量程复谱频域OCT实验系统，并为系统设计了特殊的分束镜和移相器，为最终实现复杂生物组织的OCT快速成像提供了条件．     

Detection Schemes for Optical-Coherence-Domain Imaging of Biological Tissues

Optical coherence tomography (OCT) is a novel imaging modality based on low-coherence interferometry. This paper summarizes some of our latest work on the development of OCT where we have taken two approaches. In the first approach we have developed a phase-drift-suppression method for stable heterodyne detection in the presence of phase fluctuations. In the second approach we have concentrated on the development of two-dimensional heterodyne detection techniques for real-time imaging. A novel detection scheme has been proposed, which enables parallel heterodyne detection with a commercially available imager such as a charge-coupled-device camera. Meanwhile, a non-scanning OCT system configuration based on off-axis interferometry is being studied. Using a newly developed angular-dispersion imaging scheme, we show that the axial reflectance profile in OCT measurement can be detected instantaneously with a sensor array.     

Polarisation-sensitive optical coherence tomography for material characterisation and strain-field mapping

Optical coherence tomography (OCT) is a relatively new imaging technique capable of recording cross-sectional images of transparent and turbid structures with micrometer-scale resolution. Originally developed for biomedical imaging applications, this technique also has a great potential for non-destructive material characterisation and testing. Polarisation-sensitive (PS) OCT is a recent extension of classical OCT that measures and images birefringence properties of a sample, which, however, has not yet been applied to materials science. We present imaging of glass-fibre-enforced epoxy resin compounds and the detection of dry spots, where the epoxy did not properly penetrate the glass-fibre structure. Furthermore, we demonstrate PS-OCT imaging of the birefringence properties of different materials. The mapping of strain fields of samples under uniaxial and non-uniform external stress and the detection of flow patterns in injection-moulded plastic parts could be demonstrated with this technique for the first time. Received: 21 October 2002 / Accepted: 22 November 2002 / Published online: 29 January 2003 RID="*" ID="*"Corresponding author. Fax: +43-732/9015-5618, E-mail: david.stifter@uar.at     

利用维纳滤波改善声透镜光声成像系统的分辨率

为了克服衍射效应对光声成像系统分辨率的限制,需要采用逆卷积方法进行图像反演.从理论上分析了声透镜成像原理,模拟仿真了声透镜的点扩展函数对声透镜成像系统分辨率的影响和维纳滤波解卷积方法复原光声成像的过程,并利用自搭建的声透镜光声成像系统进行了深入的实验研究,得到了物平面上相距4 mm和3 mm的两个黑胶带点的直接成像光声...     

Evaluation of bladder microvasculature with high-resolution photoacoustic imaging

We explored the potential of an emerging laser-based technology, photoacoustic imaging (PAI), for bladder cancer diagnosis through high-resolution imaging of microvasculature in the bladder tissues. Imaging results from ex vivo canine bladders demonstrated the excellent ability of PAI in mapping three-dimensional microvasculature in optically scattering bladder tissues. By comparing the results from human bladder specimens affected by cancer to those from the normal control, the feasibility of PAI to differentiate malignant from benign bladder tissues was also explored. The distinctive morphometric characteristics of tumor microvasculature can be seen in the images from cancer samples, suggesting that PAI may allow in vivo assessment of neoangiogenesis that is closely associated with bladder cancer generation and progression. By presenting subsurface morphological and physiological information in bladder tissues, PAI, when performed in a similar way as in conventional endoscopy, provides an opportunity for improved diagnosis, staging, and treatment guidance of bladder cancer.     

光学层析重建算法改进的研究

光学层析技术在温度、密度等流场的非接触测试中有着广泛的应用前景，然而光学层析的重建是非完全数据的投影重建，通常采用的代数迭代法不能很好地解决重建精度这一难题。为此提出了一种新的光学层析技术的代数迭代重建算法，在算法中引入了包含先验知识的属性矩阵，并摒弃了通常所采用的对超松弛系数人为的确定取法，采用了变超松弛系数。实验计算结果表明，引入属性矩阵和变超松弛系数的代数迭代法能够较好的重建非完全数据投影的待测场，极大地提高重建精度，较好地与实测结果吻合。     

Photoacoustic Tomography of Biological Sample Using Phase-controlled Focus Algorithm

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Photoacoustic Tomography of Biological Sample Using Phase-controlled Focus Algorithm

Photoacoustic (PA) imaging is a new imaging modality, which converts pressure signals received by a scanning detector to a local distribution of electromagnetic absorption density. In this paper an experiment result of a photoacoustic tomography to depths of ～7 mm for a real tissue is presented, using a 532-nm pulse YAG laser. The time-resolved stress detection technique was used for PA signal detection with a high temporal resolution. A phase-controlled focus algorithm was used for image reconstruction. Images of different depth profiles in tissue were obtained. The depth resolution was 30 μm and could be up to 10 μm using a wide-band tranducer.     

光声成像技术的最新进展

光声成像技术是生物医学领域中新兴的无损检测技术,具有对比度高、分辨率好、穿透能力强等优点.本文介绍了光声成像技术近年来的进展状况,主要涉及成像探测方式的改进、成像速度的加快、成像分辨率的提高以及图像重构算法的发展等.以该项技术在现代临床诊断中的应用为例,描述了其在生物医学领域中应用范围的拓宽.最后,总结了该项技术现存的...     

Holoscopy--holographic optical coherence tomography

Scanning optical coherence tomography (OCT) is limited in sensitivity and resolution by the restricted focal depth of the confocal detection scheme. Holoscopy, a combination of holography and Fourier-domain full-field OCT, is proposed as a way to detect photons from all depths of a sample volume simultaneously with uniform sensitivity and lateral resolution, even at high NAs. By using the scalar diffraction theory, as frequently applied in digital holographic imaging, we fully reconstruct the object field with depth-invariant imaging quality. In vivo imaging of human skin is demonstrated with an image quality comparable to conventionally scanned OCT.     

基于快速扫描光学延迟线谐振扫描的相位调制方法

提出利用快速扫描光学延迟线(Rapid Scanning Optical Delay Line,RSOD)作为光学相干层析成像(Optical Coherence Tomography,OCT)系统的相位调制器,并采用正弦驱动方式(谐振扫描)来提高扫描频率,进而实现高频相位调制的方法.介绍了基于RSOD相位调制器的干涉信号包络解调方法,分析了大振镜低频率线性驱动、小振镜高频线性驱动和大振镜高速正弦驱动三种实施方案对OCT性能的影响,并针对谐振扫描方案中轴向扫描的非线性提出了图像畸变定量校正的方法.结果表明:RSOD大振镜谐振扫描的模式能够兼顾系统成像速度、成像范围以及系统信噪比的要求,是一种行之有效的相位调制方法.     

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。