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.     

多模态光声分子成像进展*

现代的各种医学影像术,如射线成像、CT、正电子发射(PET)、磁共振(MR)、超声(US)、荧光(FL)等都各具特色,并成功地应用于多种疾病的诊疗。但每种影像术都不能对生物组织做出完整的描述。由若干个成像技术组成的多模态成像技术,是获得组织更多信息的有效途径。光声(PA)成像是能提供组织的成分和功能信息的新成像技术。它不仅灵敏,可以对较深层的组织进行实时、快速、安全的成像,而且可以利用光声光热造影剂实施非侵入的光热靶向治疗。因此,与光声成像相结合的多模态分子成像是实现精准诊疗的重要技术途径。该文以手持US-PA探头的双模态成像系统,直径为1 mm的血管內窥镜US-PA成像系统,可同时用于术前和术中的US-PA-FL三模态成像系统,以及采用外磁场可操控的磁共振-光声光热分子造影剂、进行MR-PA成像引导的光热治疗技术为例,对多模态光声分子成像系统在医学诊断、手术和光热治疗方面的进展做简单介绍。     

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.     

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。     

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     

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     

基于LabVIEW平台的高准确度光声成像系统设计

利用虚拟仪器开发软件LabVIEW设计了一套高准确度光声成像系统,整个系统在GPIB总线技术基础上,构架了由超声传感器、数字示波器、可调谐激光器、个人计算机等组成的硬件平台,并开发了配套的控制软件和高抗噪音图像重建算法.在活体脑结构成像中,实验鼠的左右脑、小脑、脑横裂和脑主动脉等脑结构成像清晰,大脑皮层的血管分布特征得到了完整的再现,系统成像分辨率可达200 μm.该系统和方法可望发展为一种无损伤的生物组织结构与功能成像.     

光声信号的双谱分析方法研究

基于光声效应的光声光谱技术是光学与声学的有机结合, 可利用不同波长的入射光波, 产生不同的光声信号, 从而为组分识别、组织无损检测等提供高对比度图像, 是一种极具潜力的新型医学诊断技术.但光声光谱检测技术由于受检测方法的制约, 往往扫描时间较长, 而且信号的稳定性和图像识别的准确性也较差. 为了弥补单一光声光谱分析的局限性, 根据光声效应原理和振动理论, 提出了一种光声光谱与光声频谱相结合的双谱分析方法. 该方法通过光声频域信息的定量分析, 可以有效地提高不同组织的光声图像对比度, 从而提高光声成像的组分识别能力, 为光声频谱功能成像奠定理论基础. 实验结果显示, 光声光谱与光声频谱相结合的双谱分析方法可以较好地识别实验组织样品, 可实现高速、高分辨率的组分识别、组织探伤等, 具有广泛的应用前景和重要的临床诊断意义. 关键词： 光声成像 光声光谱分析 光声频谱分析     

自适应多光谱光声成像技术研究

光声成像技术是利用激光照射组织产生超声波成像的新型医学影像技术.在传统光声成像中,由于组织体内复杂的成分与环境会对入射光波产生较大的扰动而导致波前畸变、图像分辨率下降,从而降低诊断的准确性.为了克服这一影响,本文提出了一种自适应多光谱光声成像技术.该技术利用自适应光学技术可有效地降低组织对光波扰动的影响,提高系统成像分辨率与图像对比度.此外,该系统还融合了多光谱成像技术,可在多种波长下对目标成像,从而更好地进行组织结构识别、组分分析等.实验结果表明,该系统十分适用于复杂的生物组织光声成像,可极大地增强光声成像性能,在生物医学领域具有广阔的应用前景.     

声透镜对多层样品的光声层析成像

由于光声效应产生光声压分布图像,所以当强散射介质中的模拟吸光组织在受到短脉冲激光照射时,该声压分布会经声透镜成像在像平面上。在像平面上利用线性超声探测器阵列获取光声信号并传递给高速数据采集卡进行数据采集,可由程序重构出光声图像。设计的光声层析成像系统可以采集记录一定深度的数据,成像时只要在所采集到的数据中选取不同列数即可同时获得强散射介质多层样品不同层面的光声图像。实验成功地获得了强散射介质内多层样品不同层面的光声层析图像。该成像方法无需进行复杂的算法重建,且可以同时实现多层样品不同切面的光声成像。     

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     

Dual-modal photoacoustic/CT imaging system

Photoacoustic(PA) tomography(PAT) breaks the barrier for high-resolution optical imaging in a strong lightscattering medium, having a great potential for both clinical implementation and small animal studies. However,many organs and tissues lack enough PA contrast or even hinder the propagation of PA waves. Therefore, it is challenging to interpret pure PAT images, especially three-dimensional(3 D) PA images for deep tissues, without enough structural information. To overcome this limitation, in this study, we integrated PAT with X-ray computed tomography(CT) in a standalone system. PAT provides optical contrast and CT gives anatomical information. We performed agar, tissue phantom, and animal studies, and the results demonstrated that PAT/CT imaging systems can provide accurate spatial registration of important complementary contrasts.     

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.     

Quantitative ultrasound brain imaging with multiscale deconvolutional waveform inversion

High-resolution images of human brain are critical for monitoring the neurological conditions in a portable and safe manner. Sound speed mapping of brain tissues provides unique information for such a purpose. In addition, it is particularly important for building digital human acoustic models, which form a reference for future ultrasound research. Conventional ultrasound modalities can hardly image the human brain at high spatial resolution inside the skull due to the strong impedance contrast between hard tissue and soft tissue. We carry out numerical experiments to demonstrate that the time-domain waveform inversion technique, originating from the geophysics community, is promising to deliver quantitative images of human brains within the skull at a sub-millimeter level by using ultra-sound signals. The successful implementation of such an approach to brain imaging requires the following items: signals of sub-megahertz frequencies transmitting across the inside of skull, an accurate numerical wave equation solver simulating the wave propagation, and well-designed inversion schemes to reconstruct the physical parameters of targeted model based on the optimization theory. Here we propose an innovative modality of multiscale deconvolutional waveform inversion that improves ultrasound imaging resolution, by evaluating the similarity between synthetic data and observed data through using limited length Wiener filter. We implement the proposed approach to iteratively update the parametric models of the human brain. The quantitative imaging method paves the way for building the accurate acoustic brain model to diagnose associated diseases, in a potentially more portable, more dynamic and safer way than magnetic resonance imaging and x-ray computed tomography.     

Co-registration method for photoacoustic imaging and laser speckle imaging

Combining photoacoustic (PA) imaging with laser speckle (LS) imaging (LSI) can simultaneously determine total hemoglobin concentration (HbT), hemoglobin oxygen saturation (SO2), and blood flow rates. Thus,the co-registration of PA and LS images is important in physiological studies and pathological diagnosis.This letter presents a co-registration algorithm combining mutual information with the maximum betweenclass variance segmentation method (Otsu method). The mutual information and Otsu method are used to provide the registration measure criterion and image feature recognition, respectively. The evaluation results show that the registration function possesses a single maximum peak and high smoothness across the global co-registration district, indicating a robust behavior. Moreover, this method has good registration accuracy, and the fusion result simultaneously visualizes the separate functional information of two kindsof images.     

Pixel based focusing for photoacoustic and ultrasound dual-modality imaging

It is desired that the same imaging functional modules such as beamformation, envelope detection, and digital scan conversion (DSC) are employed for the efficient development of a cross-sectional photoacoustic (PA) and ultrasound (US) dual-modality imaging system. The beamformation can be implemented using either delay-and-sum beamforming (DAS-BF) or adaptive beamforming methods, each with their own advantages and disadvantages for the dual-modality imaging. However, the DSC is always problematic because it causes blurring the fine details of an image, e.g., edges. This paper demonstrates that the pixel based focusing method is suitable for the dual-modality imaging; beamformation is directly conducted on each display pixel and thus DSC is not necessary. As a result, the artifacts by DSC are no longer a problem, so that the proposed method is capable of providing the maximum spatial resolution achievable by DAS-BF. The performance of the proposed method was evaluated through simulation and ex vivo experiments with a microcalcification-contained breast specimen, and the results were compared with those from DAS-BF and adaptive beamforming methods with DSC. The comparison demonstrated that the proposed method effectively overcomes the disadvantages of each beamforming method.     

Contrast enhanced vascular three-dimensional ultrasound imaging

In other imaging modalities three-dimensional (3D) data displays are well established; not so in ultrasound. Due to the real-time requirements of ultrasound the time available to compute 3D displays is limited, particularly when flow data is acquired with Doppler techniques. Consequently, it is only recently that improvements in computer processing power have resulted in useful vascular 3D ultrasound scans. Many manufacturers have now implemented free-hand 3D power Doppler capabilities on their scanners. However, to obtain flow signals from smaller vessels associated e.g., with tumor neovascularity, may very well require the introduction of a microbubble based ultrasound contrast agent into the blood stream. Given the up to 30 dB enhancement of Doppler signals produced by the contrast microbubbles quite spectacular vascular 3D images are feasible. Moreover, new contrast imaging techniques, such as harmonic imaging, have now permitted 3D vascular information to be acquired and displayed in grayscale with the associated improvement in resolution. In this paper we will review different aspects of contrast enhanced vascular 3D ultrasound imaging including implementation, contrast specific techniques and in vivo imaging.     

基于多元线性阵列探测器的快速光声层析成像

报道了一种基于相控聚焦的多元线性阵列探测器进行快速光声层析成像的方法和装置,并实现了模拟组织的光声层析成像。实验中采用波长为532nm脉宽为7ns的倍频Q-YAG激光器作为激发光源。多元线性阵列探测器由320个振元组成,采用相控聚焦的方法成像,每次由11个振群的探测器接受信号并合并1路,一幅图像由64路这样的信号组成。实验结果能够正确反映样品中的光学吸收分布。与现有的方法比较,本系统具有快速方便的特点,它有望成为一种组织功能在体成像的新方法,发展成为一种低成本的实用的临床诊断装置。