多参量光声成像及其在生物医学领域的应用

光声成像兼具声学成像和光学成像两者的优点, 因而成为近十年来发展最迅速的生物医学成像技术之一. 本文介绍了光声成像的特点及其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, 解释了光声成像的成像原理, 在此基础上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方案, 并介绍了它们的技术特点; 然后, 介绍了光声成像对生物组织的生化特性、组织力学特性、血液流速分布、温度分布参数、微结构特性等多信息参量的提取能力, 及其在生物系统的结构成像、功能成像、代谢成像、分子成像、基因成像等多领域的应用; 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.     

基于声学扫描振镜的超声/光声双模态成像技术

超声/光声双模态成像技术因其同时兼具超声的高分辨率结构成像和光声的高对比度功能成像优势,极大地推动了光声成像技术的临床应用推广.传统超声/光声双模态成像技术多基于超声成像所用阵列探头同时收集光声信号,系统结构紧凑且无需图像配准,操作便捷.但该类设备使用阵列探头和多通道数据采集,使得其成本较高;且成像结果易受通道一致性差异影响.本文提出了一种基于声学扫描振镜的超声/光声双模态成像技术,该技术采用单个超声换能器结合一维声学扫描振镜进行快速声束扫描,实现超声/光声双模态成像,是一种小型化、低成本的双模态快速成像技术.本文开展了系列仿体和活体成像研究,实验结果表明:系统有效成像范围为15.6 mm,超声和光声成像B扫描速度分别为1.0 s^–1和0.1 s^–1 (光声成像速度主要受制于脉冲激光器重复频率).基于本文所提技术研究,有助于进一步推动超声/光声双模态成像技术的临床转化和普及;也为基于超声信号检测的多模态成像技术提供了一种低成本、小型化和快速声信号检测的参考方案.     

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     

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...     

Method of bimodal photoacoustic and ultrasound microscopy for simultaneous structural and functional diagnostics of biotissues

The excitation of external electrode of focused photoacoustic (PA) detector by the backscattered laser radiation can ensure a cost-effective upgrade from single-modality PA microscopy to dual-modality PA/US imaging. In this work we approbated thermoelastic generation of probing ultrasonic pulses for bimodal photoacoustic (PA) and optically mediated Ultrasound (US) microscopy in vivo, using single optical pulse delivered from tunable laser to form both PA and US A-scans. The presented results of bimodal in vivo visualization of rat brain provide with the experimental evidence, that the proposed approach can be used for both functional and structural bioimaging simultaneously.     

Three-dimensional laser-induced photoacoustic tomography of mouse brain with the skin and skull intact

Three-dimensional laser-induced photoacoustic tomography, also referred to as optoacoustic tomography, is developed to image animal brain structures noninvasively with the skin and skull intact. This imaging modality combines the advantages of optical contrast and ultrasonic resolution. The distribution of optical absorption in a mouse brain is imaged successfully. The intrinsic optical contrast reveals not only blood vessels but also other detailed brain structures, such as the cerebellum, hippocampus, and ventriculi lateralis. The spatial resolution is primarily diffraction limited by the received photoacoustic waves. Imaged structures of the brain at different depths match the corresponding histological pictures well.     

In vivo dark-field reflection-mode photoacoustic microscopy

Reflection-mode photoacoustic microscopy with dark-field laser pulse illumination and high-numerical-aperture ultrasonic detection is designed and implemented in noninvasively imaged blood vessels in the skin in vivo. Dark-field optical illumination minimizes the interference caused by strong photoacoustic signals from superficial structures. A high-numerical-aperture acoustic lens provides high lateral resolution, 45-120 microm in this system. A broadband ultrasonic detection system provides high axial resolution, estimated to be approximately 15 microm. The optical illumination and ultrasonic detection are in a coaxial confocal configuration for optimal image quality. The system is capable of imaging optical-absorption contrast as deep as 3 mm in biological tissue.     

平面波经颅超声成像相位校正及散斑跟踪

准确的脑血流成像对脑功能监测和脑疾病的快速诊断具有重要意义,然而颅骨对超声传播的影响会导致成像质量下降、速度或位移估计不准确等问题.论文采用平面波相干复合结合散斑跟踪方法进行颅内散射目标成像和速度估计,以实现脑血流速度矢量检测;针对颅骨存在导致的超声相位畸变,利用数值仿真和体模实验研究了其对成像及散斑跟踪效果的影响,并...     

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...     

高分辨率快速数字化光声CT乳腺肿瘤成像

提出了一种基于聚焦线性阵列探测器的快速光声计算机断层成像技术（光声CT）.在光声二维图像重建中,根据阵列探测器机械扫描和电子扫描相结合的组合扫描模式,提出了改进的有限场滤波反投影重建算法.一方面该算法适合多元探测器旋转扫描模式,另一方面探测器的指向性函数作为反投影的权重因子提高了系统的横向分辨率.同时,该成像系统还利用柱面声透镜实现Z轴方向上的聚焦扫描以实现三维层析成像.实验中,这套成像系统空间分辨率达到0.2mm,Z轴方向分辨率为1.5mm,扫描一幅二维图像仅需150s,得到 关键词： 光声CT 有限场滤波反投影算法 声透镜聚焦 乳腺肿瘤检测     

Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans

Developing minimally invasive brain surgery by high-intensity focused ultrasound beams is of great interest in cancer therapy. However, the skull induces strong aberrations both in phase and amplitude, resulting in a severe degradation of the beam shape. Thus, an efficient brain tumor therapy would require an adaptive focusing, taking into account the effects of the skull. In this paper, we will show that the acoustic properties of the skull can be deduced from high resolution CT scans and used to achieve a noninvasive adaptive focusing. Simulations have been performed with a full 3-D finite differences code, taking into account all the heterogeneities inside the skull. The set of signals to be emitted in order to focus through the skull can thus be computed. The complete adaptive focusing procedure based on prior CT scans has been experimentally validated. This could have promising applications in brain tumor hyperthermia but also in transcranial ultrasonic imaging.     

超声平面波经颅成像相位校正方法

超声平面波经颅成像时,由于颅骨对超声传播的影响引起图像质量下降,需要对颅骨造成的超声相位畸变进行校正.为此,该文研究了两种相位补偿方法:基于近似射线声学的理论方法和基于时间反转的数值计算方法,并利用数值仿真对比了两种方法的补偿和成像效果.结果表明:无论使用近似射线法还是时间反转法,都能够有效地校正因颅骨造成的相位畸变;...     

多尺度水下偏振成像方法

水下偏振成像技术利用散射光偏振特性能够有效提高水下成像质量,在水下目标探测和识别领域具有重要应用价值.针对该技术在背景散射光和目标信息光分离时由于噪声放大现象导致重建图像质量受限的问题,提出多尺度水下偏振成像方法.该方法利用图像分层处理思想,结合小波变换的多尺度特性,对体现图像高对比度的基础层和低对比度但细节信息丰富的细节层分别进行处理,重建高对比度、高信噪比的清晰场景图像.实验结果表明,多尺度水下偏振成像方法不仅能够大幅提高对比度,复原图像细节信息,而且能够有效抑制放大噪声,提高重建图像的信噪比,在水下偏振成像领域具有良好应用前景.     

Feasibility of photoacoustic tomography for ophthalmology

For the eyeball composed of membrane and liquid, the contrast of ultrasound imaging is not high due to its small variance in acoustic impedance. As a new imaging modality, photoacoustic tomography combines the advantages of pure optical and ultrasonic imaging together and can provide high resolution, high contrast images. In this paper, the feasibility of photoacoustic tomography for ophthalmology is studied experimentally. A Q-switched Nd:YAG pulsed laser with 7-ns pulse width is used to generate photoacoustic signal of a porcine eyeball in vitro. The two-dimensional (2D) optical absorption image of the entire eyeball is reconstructed by time-domain spherical back projection algorithm. The imaging results agree well with the histological structure of the eyeball and show a high imaging contrast.     

An acoustic imaging system of migration technique used in borehole

In order to detect the damage of casing boreholes, an acoustic imaging method with a two-dimensional ultrasonic array was presented. Each element of the array independently emits down ultrasonic waves, the echoes received by all elements are sampled and transmitted to a computer on ground surface, where the dynamic migration method is used to form a 2 or 3-dimensional image of the situation in the borehole. The numerical simulation and experiment are conducted that demonstrate a high imaging accuracy with a small number of elements used in array. Since the delay circuits used in the traditional phased array imaging system is not needed in this system, and all data process could be completed in a ground system. the complexity and the volume of system in borehole may be significantly simplified, which is critical to the borehole instrument.     

基于声透镜成像系统的光声层析成像

光声成像是采用“光激发-超声波成像”的新型成像技术，它是检测强散射介质内部光吸收分布的一种有效医学影像技术.用短脉冲激光照射强散射介质(如生物组织)，强散射介质由于光声效应产生超声信号，使用具有成像能力的声透镜把声压分布成像于像面上，然后利用具有空间分辨能力的阵列光声传感器，把同一像面上的光声信号强度记录下来，最后根据光声信号强度的空间分布进行图像重组.根据成像系统物像共轭原理，同一物平面的光声信号到达像面的时延相等，而不同物面的光声信号到达同一个探测器平面的时延各不相同，因此，利用BOXCAR的门控积分 关键词： 光声层析成像 声透镜 光声信号     

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。     

Design of a novel correlative reflection electron microscope for in-situ real-time chemical analysis

A novel instrument that integrates reflection high energy electron diffraction (RHEED), electron energy loss spectroscopy (EELS), and imaging is designed and simulated. Since it can correlate the structural, elemental, and spatial information of the same surface region via the simultaneously acquired patterns of RHEED, EELS, and energy-filtered electron microscopy, it is named correlative reflection electron microscopy (c-REM). Our simulation demonstrates that the spatial resolution of this c-REM is lower than 50 nm, which meets the requirements for in-situ monitoring the structural and chemical evolution of surface in advanced material.     

Improved in vivo photoacoustic microscopy based on a virtual-detector concept

Recently an in vivo high-resolution backward-mode photoacoustic microscope was developed that shows potential for applications in dermatology and related cancer research. However, the limited depth of focus of the large-numerical-aperture (NA) ultrasonic lens employed in this system causes the image quality to deteriorate significantly in the out-of-focus region. To solve this problem, we devised and explored, for the first time to our knowledge, a virtual-detector-based synthetic-aperture focusing technique, combined with coherence weighting, for photoacoustic microscopy with such a large-NA transducer. Images of phantoms show that the proposed technique improves the -6 dB lateral resolution from 49-379 to 46-53 microm and increases the signal-to-noise ratio by up to 29 dB, depending on the distance from the ultrasonic focal point. In vivo experiments show that the technique also provides a clearer representation of the vascular distribution in the rat's scalp.     

Theory and analysis of frequency-domain photoacoustic tomography

A new frequency-domain approach to photoacoustic tomography has recently been proposed, promising to overcome some of the shortcomings associated with the pulsed photoacoustic approach. This approach offers many of the benefits of pulsed photoacoustics but requires a different set of equations for modeling of the forward and inverse problems due to the longer time scales involved in the optical input signal. The theory of photoacoustic tomography with an optical input that is not necessarily a short pulse is considered in this paper. The full optical, thermal, and acoustic governing equations are derived. A transfer function approach is taken for the solution and analysis of this problem. The results and implications are compared with those of pulsed photoacoustics and traditional ultrasonic diffraction tomography. A Fourier diffraction theorem is also presented, which could be used as a basis for the development of tomographic imaging algorithms.