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.     

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.     

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     

超声换能器带宽对光声成像的影响

研究了不同尺寸吸收体产生的光声压的频谱特性：对于厘米量级、毫米量级和几百个微米量级的吸收体,产生光声压频谱的主要范围分别约为20～300kHz、70kHz～2．5MHz和400kHz～20MHz;讨论了不同频率范围的光声信号对重建图像的影响,低频段的光声信号能反映物体的非边界区域,而高频段的光声信号能突出物体的细微结构,尤其是物体的边界特征。提出了不同尺寸的吸收体要选用或设计不同带宽范围的探测器进行检测的方法．当探测器的带宽范围与光声压频谱范围基本吻合时,损失的频率成份较少,重建的光声图像效果较好,这一结论在仿真和实验结果中都得到了证明。实验用的光源为YAG激光器,波长为532nm,重复频率为30Hz,脉宽为7ns,探测器为针状的PVDF膜水听器,接收面积的直径为1mm。     

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.     

Single-wavelength functional photoacoustic microscopy in biological tissue

Recently, we developed a reflection-mode relaxation photoacoustic microscope, based on saturation intensity, to measure picosecond relaxation times using a nanosecond laser. Here, using the different relaxation times of oxygenated and deoxygenated hemoglobin molecules, both possessing extremely low fluorescence quantum yields, the oxygen saturation was quantified in vivo with single-wavelength photoacoustic microscopy. All previous functional photoacoustic microscopy measurements required imaging with multiple-laser-wavelength measurements to quantify oxygen saturation. Eliminating the need for multiwavelength measurements removes the influence of spectral properties on oxygenation calculations and improves the portability and cost-effectiveness of functional or molecular photoacoustic microscopy.     

Photoacoustic Tomography of Biological Sample Using Phase-controlled Focus Algorithm

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Copper Sulfide Nanodisks and Nanoprisms for Photoacoustic Ovarian Tumor Imaging

Transvaginal ultrasound is widely used for ovarian cancer screening but has a high false‐positive rate. Photoacoustic imaging provides additional optical contrast to supplement ultrasound and might be able to improve the accuracy of screening. Two copper sulfide (CuS) nanoparticle types (nanodisks and triangular nanoprisms) are reported as photoacoustic contrast agents for imaging ovarian cancer. Both CuS nanoprisms and nanodisks are ≈6 nm thick and ≈26 nm wide and are coated with poly(ethylene glycol) to make them colloidally stable in phosphate‐buffered saline for at least two weeks. The CuS nanodisks and nanoprisms reveal strong localized surface plasmon resonances with peak maxima at 1145 and 1098 nm, respectively. Both nanoparticle types have strong and stable photoacoustic intensity with detection limits below 120 pm . The circular CuS nanodisk remains in the circulation of nude mice (n = 4) and xenograft 2008 ovarian tumors (n = 4) 17.9‐fold and 1.8‐fold more than the triangular nanoprisms, respectively. Finally, the photoacoustic intensity of the tumors from the mice (n = 3) treated with CuS nanodisks is threefold higher than the baseline. The tumors treated with nanodisks have a characteristic peak at 920 nm in their spectrum to potentially differentiate the tumor from adjacent tissues.     

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     

A miniature prototype of a resonance photoacoustic cell for gas sensing

We present a miniature prototype of a resonance photoacoustic cell with a banana-shaped internal cavity with a volume of less than ～5 mm³. The cell design and the experimental setup used for testing operational characteristics of the prototype are described. The results of testing the prototype in the experiments on photoacoustic detection of radiation absorption by ammonia in a nitrogen flow by using a single-mode diode laser generating radiation near ～1.53 μm are presented. The amplitude-frequency characteristic of the photoacoustic response induced by absorption of radiation in the presence and absence of ammonia is analyzed. The experiment revealed that sensitivity of gas sensing is limited only by the microphone noise. The measured noise-limited minimal detectable absorption was found to be about 8.48 × 10^?8 cm^?1 W Hz^?1/2.     

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     

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.     

Spectral imaging of neurosurgical target tissues through operation microscope

It has been noticed that spectral information can be used for analyzing and separating different biological tissues. However, most of the studies for spectral image acquisitions are mainly done in vitro. Usually the main restrictions for in vivo measurements are the size or the weight of the spectral camera. If the camera weights too much, the surgery microscope cannot be stabilized. If the size of the camera is too big, it will disturb the surgeon or even risk the safety of the patient. The main goal of this study was to develop an independent spectral imaging device which can be used for collecting spectral information from the neurosurgeries without any previously described restrictions. Size of the imaging system is small enough not to disturb the surgeon during the surgery. The developed spectral imaging system is used for collecting a spectral database which can be used for the future imaging systems.     

Noninvasive detection of intimal xanthoma using combined ultrasound, strain rate and photoacoustic imaging

Background and motivation

The structure, composition and mechanics of carotid artery are good indicators of early progressive atherosclerotic lesions. The combination of three imaging modalities (ultrasound, strain rate and photoacoustic imaging) which could provide corroborative information about the named arterial properties could enhance the characterization of intimal xanthoma.

Methods

The experiments were performed using a New Zealand white rabbit model of atherosclerosis. The aorta excised from an atherosclerotic rabbit was scanned ex vivo using the three imaging techniques: (1) ultrasound imaging of the longitudinal section: standard ultrasound B-mode (74 Hz frame rate); (2) strain rate imaging: the artery was flushed with blood and a 1.5 Hz physiologic pulsation was induced, while the ultrasound data were recorded at higher frame rate (296 Hz); (3) photoacoustic imaging: the artery was irradiated with nanosecond pulsed laser light of low fluence in the 1210-1230 nm wavelength range and the photoacoustic data was recorded at 10 Hz frame rate. Post processing algorithms based on cross-correlation and optical absorption variation were implemented to derive strain rate and spectroscopic photoacoustic images, respectively.

Results

Based on the spatio-temporal variation in displacement of different regions within the arterial wall, strain rate imaging reveals differences in tissue mechanical properties. Additionally, spectroscopic photoacoustic imaging can spatially resolve the optical absorption properties of arterial tissue and identify the location of lipid pools.

Conclusions

The study demonstrates that ultrasound, strain rate and photoacoustic imaging can be used to simultaneously evaluate the structure, the mechanics and the composition of atherosclerotic lesions to improve the assessment of plaque vulnerability.     

时域两维荧光寿命显微测量研究

提出了一种新的时域两维荧光寿命显微测量技术,建立了一套荧光寿命成像显微系统,介绍了这种测量技术的数据处理方法。用标准样品对该系统进行了测试,实验表明,该系统的时间分辨率为2ps,在放大倍率为100倍的情况下,该系统的空间分辨率为8um。如果在现有的设备下采用更细的网格板和微位移系统,那么该系统的空间分辨率可小于1um.     

Assessment of tumor vasculature for diagnostic and therapeutic applications in a mouse model in vivo using 25-MHz power Doppler imaging

Objective

The blood flow rate in the microcirculation associated with angiogenesis plays an important role in the progression and treatment of cancer. Since the microvascular status of tumor vessels can yield useful clinical information, assessing changes in the tumor microcirculation could be particularly helpful for tumor evaluation and treatment planning.

Methods

In this study we used a self-developed 25-MHz ultrasound imaging system with a spatial resolution of 150 μm for assessing tumor-microcirculation development and the pattern of the vasculature in three tumor-bearing mice in vivo based on power Doppler images. The total Doppler power (DP) and color pixel density (CPD) revealed the presence of functional vessels distributed throughout a tumor volume. The vasculature distributions in the core and periphery were compared to the regulation of vasculature function, which facilitated determination of when the tumor grew rapidly.

Results

The data obtained from a quantified analysis of power Doppler images indicated that the tumor vascularity initially increased throughout the tumor. Both DP and CPD increased rapidly in the tumor periphery when the tumor volume exceeded 10 mm³.

Conclusion

Our preclinical findings suggest that power Doppler imaging could be useful for detecting the changes in tumor vascular perfusion and for determining the optimal treatment timing when a tumor begins its rapid volumetric growth.     

Multi-parameter diagnostics for high-resolution in-situ measurements of single coal particle combustion

To study volatile combustion processes of single coal particles non-intrusive simultaneous multi-parameter measurements were performed. The experiment was carried out in a fully premixed flat flame burner with well-defined boundary conditions. For flame visualization high-speed luminescence imaging was combined with high-resolution high-speed OH-PLIF. To address particle size and shape a stereoscopic high-resolution backlight-illumination system was set up. Due to simultaneous recording of individual particle events the volatile combustion duration related to particle size, shape and velocity was measured. A comparison of luminescence imaging and OH-PLIF for flame visualization was investigated to define their application areas in coal combustion. The stereoscopic backlight-illumination setup was benchmarked to a well characterized bituminous coal. With a pixel resolution of ～2.5 µm fine particle contours were resolved. The particle diameter and eccentricity were evaluated by an ellipse approximation. The experimental setup can be used to investigate different coal ranks and biomass in N₂/O₂ and CO₂/O₂ atmospheres in future.     

CO2 laser photoacoustic spectra and vibrational modes of heroin, morphine and narcotine

Heroin, morphine and narcotine are very large molecules having 50, 40 and 53 atoms respectively. Moderately high resolution photoacoustic (PA) spectra have been recorded in 9.6 μm and 10.6 μm regions of CO₂ laser. It is very difficult to assign the modes of vibrations for PA bands by comparison with conventional low resolution IR spectra. The ab initio quantum chemical calculations were used for determining the molecular geometries and normal mode frequencies of vibrations of these molecules for assignments of PA spectra.     

X射线掠入射显微成像诊断技术研究进展

高精密的X射线成像诊断是深入理解内爆过程，揭示点火尺度下未知物理问题的关键。基于掠入射反射的X射线显微镜，结合亚纳米级的超光滑球面或非球面反射镜，能够实现空间分辨优于5 μm的高分辨成像。介绍了国际惯性约束聚变领域的X射线显微成像技术发展及应用，重点展示了我国在高分辨X射线（KB）显微镜、多通道X射线KB显微镜以及大视场X射线KBA显微镜方向的进展，分析了下一阶段超高分辨X射线显微成像的研究计划。通过不断的技术创新，我国的X射线显微成像诊断能力已经达到国际先进水平。     

单色化X射线显微成像实验研究

围绕激光惯性约束聚变(ICF)内爆压缩阶段高空间分辨、高能谱分辨的诊断需求,提出了一种将KB显微镜和衍射晶体组合的大视场、单色化成像系统。在实验室条件下,利用Fe靶X射线光管,采用KB显微镜结合高定向热解石墨(HOPG)对网格进行背光成像,晶体选能后的成像结果表明,系统的视场能达到800μm,其中高分辨区域成像的分辨率为37μm。采用能谱探测器测试成像能谱,结果表明,系统的能量分辨率为28,验证了系统的单色性能。该系统兼顾了大视场、空间分辨和能量分辨,对内爆压缩阶段实验中热斑结构及混合效应的研究具有重要应用。