基于时域光声信号的谱分析技术及其在生物医学领域的应用

基于时域光声信号的谱分析技术是一种能够提供生物组织结构和功能信息的非侵入式检测技术,其结合了光学模态的高对比度和超声模态在深层组织中的高分辨率两重特性,可对不同波长光激发下的目标生物组织的光声信号数据集进行处理分析。相较于传统光谱检测,该技术不易受被测对象形状、形态的限制和光散射的影响,使其对较深层组织的检测仍具有较高灵敏度。相较于光声成像,该技术无需引入图像重建算法且专注于实现定量分析。综述时域光声信号的谱分析技术在生物组织、生物体液、生物呼出气体检测中的应用,介绍相关研究所采用的改进实验系统或不同信号处理方法,阐述该技术的研究进展与发展方向。     

时域光声谱法在生物医学领域中的应用及进展

基于光声效应的时域光声光谱法将光学与声学有效结合起来，部分克服了组织的强散射性对测量结果的影响，具有灵敏度高、分辨力高等优点，广泛应用于生物医学领域。文中综合论述了时域光声谱法测量原理、关键技术，应用及将来时域光声谱法研究的发展方向，以进一步推动理论及应用研究的工作。     

光动力学疗法和声动力学疗法

目的:通过对肿瘤治疗中光动力学疗法和声动力学疗法的研究现状及研究进展的综述,以期对临床应用或实验研究起到一定的借鉴作用。方法:本文具体阐述了光动力学疗法和声动力学疗法杀伤肿瘤细胞的分子机制以及光敏剂与声敏剂的分类,介绍了两种方法在肿瘤方面的应用及对新的治疗模式的探索,展望了光动力学疗法和声动力学疗法临床应用的巨大潜力。结果:光动力学疗法和声动力学疗法的研究已取得了一定的成果,但在组织内氧含量、新型光敏剂与声敏剂的开发、药物剂量的把握及对声动力学疗法作用机理的研究方面仍存在问题。结论:光动力学疗法和声动力学疗法作为两种新的肿瘤治疗手段,在肿瘤的防治中已展现出良好的应用前景,但在临床实际应用中光动力学疗法还未普及,而声动力学疗法起步较晚,尚处于研究阶段,未应用于临床。     

光声技术在癌症检测和非侵犯性诊断中的应用（英文）

目的：探讨光声技术的原理、优势及癌症临床应用前景。方法：根据肿瘤发展过程,相继介绍光声技术在肿瘤检测过程中的应用。结果：光声技术对光散射生物组织-肿瘤,能够进行无损深层探测及成像,具有其他成像技术所无法比拟的优势。结论：光声技术是一种新的发展中的成像模式,应用于生物医药并获得解剖和功能信息。它对于了解肿瘤生长、转移,癌症诊断和评测治疗功效都有着潜在的重大用途。     

拉曼光镊技术在不同细胞中应用的进展

目的:引入并介绍拉曼光谱、光镊的物理原理及其工作特点.结合详细的医学研究工作,总结了拉曼光镊技术在不同细胞领域的具体应用情况.方法:采用光镊固定活细胞,同时应用激光拉曼技术对活细胞进行活细胞或细胞器的拉曼光谱测定,应用此技术俘获悬浮液中的样品,在接近生理状态下研究单个活体,如细胞、细胞器或生物大分子,对研究对象的生理生化过程可进行实时跟踪,进而对活细胞进行拉曼光谱测定.结果:光镊拉曼光谱技术从单细胞水平分析正常人红细胞和地中海贫血患者的红细胞的携氧能力和形变能力,实现对不同物种血红细胞和血小板鉴定;拉曼光谱技术在分子水平上揭示癌细胞组织结构与正常细胞组织结构之间的差异,为癌症诊断和机理分析提供重要的信息和数据:拉曼光谱技术实现了DNA分子的扭转和打结,并实现了对人类染色体操控和鉴别.结论:拉曼光镊技术是实时研究细胞生理、生化变化的快捷而有效的工具,有望成为在分子水平上对各种活细胞的检测、诊断的先进工具,具有非常广阔的前景.     

血管内光声成像的研究进展

血管内光声（IVPA）成像是近年来发展起来的一种微创血管内成像技术,结合了光声信号激发阶段光吸收较高的对比度和光声信号发射阶段超声检测较高的分辨率,根据斑块成分对光的吸收差异检测和区分动脉粥样硬化斑块,可对斑块的形态和成分做更为全面的了解。介绍IVPA成像系统的研究现状、血管内超声(IVUS)/IVPA组合成像导管的设计与改进,以及在光谱成像、热成像、分子成像和对冠状动脉支架成像方面的应用现状,指出目前存在的问题,并对未来的研究进行展望。     

血糖浓度光声光谱检测技术的研究

传统血糖检测需要从患者静脉取血,给患者带来了极大的痛苦和经济负担.本研究利用光声光谱(PAS)高灵敏性和无损的特点,进行血糖光声光谱分析.实验分别采集葡萄糖粉末、血清、红细胞和全血的光声光谱,利用小波变换对采集信号进行降噪处理.结果显示:全血的光声谱中670nm附近,有明显的葡萄糖特征峰,且峰值强度随血糖浓度有相应变化.本研究为血糖光声光谱无创检测提供了一定的实验依据.     

基于焦区积分的高分辨率光声变焦显微成像

光声显微成像兼具高光学组织对比度,以及超声的高穿透深度和高空间分辨率的优点。但一方面在光声显微成像中,组织深层目标易被浅表目标屏蔽,另一方面其横向分辨率与焦深的矛盾一直限制了光声显微的成像质量。针对这两个问题,本实验搭建了一套基于超声分辨的光声显微成像系统。其采用一种非共轴的照明-探测方式来减少浅层组织对深层信息的影响,并且采用一种新的焦区积分算法来进行数据的处理,结合多次纵向变焦扫描来实现深层组织的高分辨探测。仿体实验表明,该方法可以在不同纵向深度上保持约0.6 mm的横向分辨率,与理论值相接近。裸鼠肿瘤成像结果表明,本文所提出的方法可以比普通的背向探测声聚焦光声显微成像方法在深度方向上获取更多的信息。随着超快脉冲激光和高速扫描方式的发展,本文所提出的方法有望在脑部血管成像、宫颈癌内窥成像、浅表肿瘤成像等方面得到较好的应用。     

生物组织非接触光声层析成像EI北大核心CSCD

在光声成像中,超声信号通常需要采用接触传感器探测,这使其在很多应用中受到很大的限制,如脑功能成像。为了替代接触探测器实现非接触的光声层析成像(NCPAT),激光干涉技术被用于远程获取超声信号。本文搭建了非接触光声层析成像系统,系统采用波长为532 nm、能量17.5 m J/cm^2的激光作为光声激发源,激光外差干涉仪作为光声信号的远程探测系统,对实际生物组织模型进行了旋转几何的光声信号探测。利用激光外差干涉仪探测到的光声信号,进行反投影算法的图像重建。实验结果表明在具有组织散射特性的模型中,激光外差干涉仪在2.25 MHz带宽(峰值下15 d B强度的信号宽带)下,NCPAT成像系统可以识别500μm直径的黑色微球,并实现了在强散射介质中多层结构的光学对比成像。这将扩展光声和超声在体成像在生物医学领域的应用范围。     

提高光声成像质量的Renyi熵方法

针对光声成像数据采集系统中获得的超声数据存在杂波问题,提出一种先基于Renyi熵分离超声信号和杂波,再利用分离后的超声数据进行光声成像的方法。光声成像平台实验表明,通过Renyi熵的直方图来选择超声信号和杂波分离的阈值,可以有效地滤除超声信号中的大部分杂波。成像重构的评估结果也验证了该结论。可见,该文提出的方法能有效滤除超声采集数据中的杂波,从而提高光声成像的质量。     

模拟微血管的光声成像技术研究

目的：为了实现较深层组织内微血管的光声成像。方法：采用波长532nm、重复频率10Hz的脉冲激光作为激励源,宽带非聚焦针状探头以圆周扫描的方式采集时域光声信号,二维光学吸收分布图像由时域后向投影算法重建,以线扩展函数为依据测量系统的成像空间分辨率。结果：成像空间分辨率0．1mm,模拟微血管网络的光声图像与原始样品完全吻合。结论：对组织内癌症病灶的早期诊断具有较大的意义。     

Performance of a lookup table-based approach for measuring tissue optical properties with diffuse optical spectroscopy

Diffuse optical spectroscopy (DOS) provides a powerful tool for fast and noninvasive disease diagnosis. The ability to leverage DOS to accurately quantify tissue optical parameters hinges on the model used to estimate light-tissue interaction. We describe the accuracy of a lookup table (LUT)-based inverse model for measuring optical properties under different conditions relevant to biological tissue. The LUT is a matrix of reflectance values acquired experimentally from calibration standards of varying scattering and absorption properties. Because it is based on experimental values, the LUT inherently accounts for system response and probe geometry. We tested our approach in tissue phantoms containing multiple absorbers, different sizes of scatterers, and varying oxygen saturation of hemoglobin. The LUT-based model was able to extract scattering and absorption properties under most conditions with errors of less than 5 percent. We demonstrate the validity of the lookup table over a range of source-detector separations from 0.25 to 1.48 mm. Finally, we describe the rapid fabrication of a lookup table using only six calibration standards. This optimized LUT was able to extract scattering and absorption properties with average RMS errors of 2.5 and 4 percent, respectively.     

In vivo cerebrovascular measurement combining diffuse near-infrared absorption and correlation spectroscopies

We combine two near-infrared diffuse optical techniques to study variations of blood flow, haemoglobin concentration, and blood oxygen saturation in the functioning rat brain. Diffuse correlation spectroscopy (or flowmetry) monitors changes in the cerebral blood flow, without the use of the principles of tracer clearance, by measuring the optical phase-shifts caused by moving blood cells. Near-infrared absorption spectroscopy concurrently measures tissue absorption at two wavelengths to determine haemoglobin concentration and blood oxygen saturation in this same tissue volume. This optical probe is non-invasive and was employed through the intact skull. The utility of the technique is demonstrated in vivo by measuring the temporal changes in the regional vascular dynamics of rat brain during hypercapnia. Temporal and spatial variations of cerebral blood flow, haemoglobin concentration and blood oxygen saturation during hypercapnia are compared with other measurements in the literature, and a quantitative analysis demonstrating the self-consistency of our combined observations of vascular response is presented.     

Determination of visible near-IR absorption coefficients of mammalian fat using time- and spatially resolved diffuse reflectance and transmission spectroscopy

In-vivo optical spectroscopy and the determination of tissue absorption and scattering properties have a central role in the development of novel optical diagnostic and therapeutic modalities in medicine. A number of techniques are available for the optical characterization of tissue in the visible near-IR region of the spectrum. An important consideration for many of these techniques is the reliability of the absorption spectrum of the various constituents of tissue. The availability of accurate absorption spectra in the range 600 to 1100 nm may allow for the determination of the concentration of key tissue constituents such as oxy- and deoxy-hemoglobin, water, and lipids. The objective of the current study is the determination of a reliable absorption spectrum of lipid(s) that can be used for component analysis of in-vivo spectra. We report the absorption spectrum of a clear purified oil obtained from pig lard. In the liquid phase above 36 degrees C, the oil is transparent and thus suitable for collimated transmission measurements. At room temperature, the oil is a solid grease that is highly scattering. The absorption and scattering properties in this solid phase are measured using time- and spatially resolved diffuse reflectance spectroscopy. Using these three independent measurement techniques, we have determined an accurate estimate for the absorption spectrum of mammalian fat.     

In vivo low-coherence spectroscopic measurements of local hemoglobin absorption spectra in human skin

Localized spectroscopic measurements of optical properties are invaluable for diagnostic applications that involve layered tissue structures, but conventional spectroscopic techniques lack exact control over the size and depth of the probed tissue volume. We show that low-coherence spectroscopy (LCS) overcomes these limitations by measuring local attenuation and absorption coefficient spectra in layered phantoms. In addition, we demonstrate the first in vivo LCS measurements of the human epidermis and dermis only. From the measured absorption in two distinct regions of the dermal microcirculation, we determine total hemoglobin concentration (3.0±0.5 g∕l and 7.8±1.2 g∕l) and oxygen saturation.     

Spectra from 2.5-15 microm of tissue phantom materials,optical clearing agents and ex vivo human skin: implications for depth profiling of human skin

Infrared measurements have been used to profile or image biological tissue, including human skin. Usually, analysis of such measurements has assumed that infrared absorption is due to water and collagen. Such an assumption may be reasonable for soft tissue, but introduction of exogenous agents into skin or the measurement of tissue phantoms has raised the question of their infrared absorption spectrum. We used Fourier transform infrared spectroscopy in attenuated total reflection mode to measure the infrared absorption spectra, in the range of 2-15 microm, of water, polyacrylamide, Intralipid, collagen gels, four hyperosmotic clearing agents (glycerol, 1,3-butylene glycol, trimethylolpropane, Topicare), and ex vivo human stratum corneum and dermis. The absorption spectra of the phantom materials were similar to that of water, although additional structure was noted in the range of 6-10 microm. The absorption spectra of the clearing agents were more complex, with molecular absorption bands dominating between 6 and 12 microm. Dermis was similar to water, with collagen structure evident in the 6-10 microm range. Stratum corneum had a significantly lower absorption than dermis due to a lower content of water. These results suggest that the assumption of water-dominated absorption in the 2.5-6 microm range is valid. At longer wavelengths, clearing agent absorption spectra differ significantly from the water spectrum. This spectral information can be used in pulsed photothermal radiometry or utilized in the interpretation of reconstructions in which a constant mu(ir) is used. In such cases, overestimating mu(ir) will underestimate chromophore depth and vice versa, although the effect is dependent on actual chromophore depth.     

Immobilization of a nonsteroidal antiinflammatory drug onto commercial segmented polyurethane surface to improve haemocompatibility properties

A method has been developed in which a layer of p-aminosalicylic acid (4-amino-2-hydroxybenzoic acid) (PAS), a water soluble pharmaceutical compound of the nonsteroidal anti-inflammatory drug (NSAID) class with antiaggregant platelet activity, is covalently immobilized onto a segmented polyurethane, Biospan (SPU) surface. Thus, SPU surfaces were modified by grafting of hexamethylenediisocyanate. and the free isocyanate remaining on the SPU surface were then coupled through a condensation reaction to amine groups of p-aminosalicylic acid. The bonding of PAS from aqueous solution onto SPU surface was studied by ATR-FTIR. UV and fluorescence spectroscopy. Plateau levels of coupled PAS were reached within 1.2 microg/cm2 using PAS solution concentrations of 1mg/ ml. The surface wettability of the polymeric films measured by contact angle indicate that the introduction of the PAS turns the surface more hydrophilic (theta(water) = 43.1 +/- 2.1) relatively to the original SPU films (theta(water) = 70.3 +/- 1.9). The in vitro albumin (BSA) adsorption shows that the PAS-SPU films adsorb more BSA (250/microgmm2) than the original SPU (112 microg mm2). Thrombogenicity was assessed by measuring the thrombus formation and platelet adhesion of the SPU containing PAS relatively to nonmodified SPU surfaces. The polymeric surfaces with immobilized PAS had better nonthrombogenic characteristics as indicated by the low platelet adhesion, high adsorption of albumin relatively to fibrinogen and low thrombus formation, making them potentially good candidates for biomedical applications.     

Photoacoustic probing of fluorophore excited state lifetime with application to oxygen sensing

A new method is developed to perform local measurements of fluorophore excited state lifetimes in turbid media without collecting the fluorescence emission. The method is based on a pump-probe approach where a first laser pulse excites the dye and then a second laser pulse is used for photoacoustic probing of the transient absorption. The photoacoustic response generated by the probe pulse is recorded by an ultrasound receiver. Repeating the measurement for increasing pump-probe time delays yields a series of photoacoustic signals that are used to extract the lifetime of the excited state. The method is validated by measuring the lifetime of an oxygen sensitive dye solution at different concentrations of dissolved oxygen. The dye is pumped with a 532-nm pulsed laser and the transient absorption at 740 nm is probed using a second pulsed laser system. The photoacoustic-based results are in close agreement with those obtained from time-dependent fluorescent measurements. The method can be extended to photoacoustic lifetime imaging by using a receiver array instead of a single receiver. Potential applications of this method include tissue oxygen imaging for cancer diagnostics and mapping molecular events such as resonant energy transfer and ion collisions in a biological environment.