Photoacoustic molecular imaging with functional nanoparticles

Photoacoustic imaging(PAI)breaks through the optical di®usion limit by making use of the PA e®ect.By converting incident photons into ultrasonic waves,PAI combines high contrast of optical imaging and high spatial resolution in depth tissue of ultrasound imaging in a single imaging modality.This imaging modality has now shown potential for molecular imaging,which enables visualization of biological processes with systemically introduced functional nanoparticles.In the current review,the potentials of di®erent optical nanoprobes as PAI contrast agents were elucidated and discussed.

Highly Sensitive MoS_2–Indocyanine Green Hybrid for Photoacoustic Imaging of Orthotopic Brain Glioma at Deep Site

Photoacoustic technology in combination with molecular imaging is a highly effective method for accurately diagnosing brain glioma. For glioma detection at a deeper site, contrast agents with higher photoacoustic imaging sensitivity are needed. Herein, we report a MoS_2–ICG hybrid with indocyanine green(ICG) conjugated to the surface of MoS_2 nanosheets. The hybrid significantly enhanced photoacoustic imaging sensitivity compared to MoS_2 nanosheets. This conjugation results in remarkably high optical absorbance across a broad near-infrared spectrum, redshifting of the ICG absorption peak and photothermal/photoacoustic conversion efficiency enhancement of ICG. A tumor mass of 3.5 mm beneath the mouse scalp was clearly visualized by using MoS_2–ICG as a contrast agent for the in vivo photoacoustic imaging of orthotopic glioma, which is nearly twofold deeper than the tumors imaged in our previous report using MoS_2 nanosheet. Thus, combined with its good stability and high biocompatibility, the MoS_2–ICG hybrid developed in this study has a great potential for high-efficiency tumor molecular imaging in translational medicine.

SIMULTANEOUS IMAGING OF A lacZ-MARKED TUMOR AND MICROVASCULATURE MORPHOLOGY IN VIVO BY DUAL-WAVELENGTH PHOTOACOUSTIC MICROSCOPY

Photoacoustic molecular imaging,combined with the reporter-gene technique,can provide a valuable tool for cancer research.The expression of the lacZ reporter gene can be imaged using photoacoustic imaging following the injection of X-gal,a colorimetric assay for the lacZ-encoded enzymeβ-galactosidase.Dual-wavelength photoacoustic microscopy was used to non-invasively image the detailed morphology of a lacZ-marked 9L gliosarcoma and its surrounding microvasculature simultaneously in vivo,with a superior resolution on the order of 10μm.Tumor-feeding vessels were found,and the expression level of lacZ in tumor was estimated.With future development of new absorption-enhancing reporter-gene systems,we anticipate this strategy can lead to a better understanding of the role of tumor metabolism in cancer initiation,progression,and metastasis,and in its response to therapy.

Photoacoustic mesoscopy:pushing toward the depth limit in the high-resolution optical imaging for biomedical applications and clinical potentials

Photoacoustic mesoscopy(PAMe) offers high-sensitivity in vivo imaging based on the rich optical contrast in biological tissues,with sub-100-micron resolutions at a few millimeters depth. By benefiting from low ultrasonic scattering,this emerging technology has pushed the penetration depth beyond the optical diffuse limit unprecedented for high-resolution optical methods.Here,we review ed the state-of-art implementations of PAMe and their achievements in biological and primary clinical applications. With the high-frequency focused ultrasonic detector,the high-resolution optical visualization can be achieved by utilizing various PAMe systems. These capabilities of PAMe have made it well applicable for understanding the biological mechanisms,exploring the pathological features and analyzing the characteristics of human skin. Future improvements and prospects of PAMe are also mentioned,suggesting its great potential tow ards the corresponding emerging biomedical and clinical applications.

Noncontact photoacoustic lipid imaging by remote sensing on first overtone of the C-H bond

Lipid imaging by conventional photoacoustic microscopy subjects to direct contact sensing with relatively low detection bandwidth and sensitivity,which induces superficial imaging depth and low signalto-noise ratio(SNR)in practical imaging scenarios.Herein,we present a photoacoustic remote sensing microscopy for lipid distribution mapping in bio-tissue,featuring noncontact implementation,broad detection bandwidth,deep penetration depth,and high SNR.A tailored high-energy pulsed laser source with a spectrum centered at 1750 nm is used as the excitation beam,while a cofocused 1550 nm continuous-wave beam is used as the probe signal.The pump wavelength is selected to overlap the first overtone of the C-H bond in response to the intensive absorption of lipid molecules,which introduces a much-enhanced SNR(55 dB)onto photoacoustic remote sensing(PARS)signals.Meanwhile,the optical sensing scheme of the photoacoustic signals provides broadband detection compared to the acoustic transducer and refrains the bio-samples from direct contact operations by eliminating the ultrasonic coupling medium.Taking merits of the high detection sensitivity,deep penetration depth,broadband detection,and high resolution of the PARS system,high-quality tissue scale lipid imaging is demonstrated in a model organism and brain slice.

Encapsulated Fe(IV)Molecular Complex for Photoacoustic Imaging

stable neutral Fe(IV)complex(Fe-HDCL),readily accessible on the g scale,was found to possess high water solubility and good stability(<5%degradation over 4 h upon photoirradiation).Fe-HDCL is green and absorbs light effectively in the visible region(500–800 nm)with aλmax at 650 nm(ɛ=7830 M^(−1)cm^(−1)).Fe-HDCL also exhibits photothermal(PT)behavior comparable to single-wall carbon nanotubes in the solid state.In aqueous solution,high PT conversion(η=72.6%)is achieved,and a strong hyperthermia-based inhibition of cell growth is observed upon subjecting Fe-HDCL to near-infrared 730 nm laser photoirradiation.Initial biological studies in vitro and in vivo confirmed that Fe-HDCL is biocompatible,clears readily,and allows the visual detection of blood vessels.Upon subjecting mice to intravenous injection at low doses(e.g.,50μmol·kg^(−1)),Fe-HDCL also permits the photoacoustic(PA)imaging of kidneys and the evaluation of renal fibrosis in mouse models.In addition,Fe-HDCL allows PA-based imaging of brain tissues,presumably reflecting its ability to pass through the blood-brain barrier.We thus propose that Fe-HDCL has a role to play as PT agent and as a photodiagnostic.

Functional imaging and endoscopy

The emergence of endoscopy for the diagnosis of gastrointestinal diseases and the treatment of gastrointestinal diseases has brought great changes.The mere observation of anatomy with the imaging mode using modern endoscopy has played a significant role in this regard.However,increasing numbers of endoscopies have exposed additional deficiencies and defects such as anatomically similar diseases.Endoscopy can be used to examine lesions that are difficult to identify and diagnose.Early disease detection requires that substantive changes in biological function should be observed,but in the absence of marked morphological changes,endoscopic detection and diagnosis are difficult.Disease detection requires not only anatomic but also functional imaging to achieve a comprehensive interpretation and understanding.Therefore,we must ask if endoscopic examination can be integrated with both anatomic imaging and functional imaging.In recent years,as molecular biology and medical imaging technology have further developed,more functional imaging methods have emerged.This paper is a review of the literature related to endoscopic optical imaging methods in the hopes of initiating integration of functional imaging and anatomical imaging to yield a new and more effective type of endoscopy.

Minimally Invaded Sentinel Lymph Node Model for the Development of Intraoperative Infrared Fluorescence Imaging

In this study we implemented an axillary SLN invasion model to develop highly sensitive imaging strategies enabling detection of a very small amount of tumor cells. A highly diffusible molecular probe targeting &alpha;v&beta;3 and &alpha;v&beta;5 integrins was investigated either via IV or locoregional injections. We additionally documented the potential interferences of this Near Infrared Fluorescence Probe with Blue Patente V and ICG dyes routinely used to facilitate lymph node detection during surgery. The human mammary adenocarcinoma MDA-MB-231-luc model was injected into the forepaw of nude female rats to obtain a controlled invasion of the axillary LN. Thanks to its high sensitivity, BLI was selected to achieve in vivo quantitation of tumor cells in SLNs and determine eligible animals for the study. NIRF of integrins was performed at 680 nm both in vivo and ex vivo using spectral unmixing to suppress auto-fluorescence signal and preserve sensitivity. In vivo BLI was quite reliable in estimating discrete invasion by cancer cells in the LN with thresholds of detection and quantitation of about 500 and 1500 cells respectively. For fluorescence at 680 nm, in vivo imaging is not suitable to detect micro-invasion, but ex vivo fluorescence with spectral unmixing of SLNs confirmed the presence of a tumor burden as low as 1500 cells expressing &alpha;v&beta;3/&alpha;v&beta;5 integrins. Targeting few tumor cells inside a micro-invaded sentinel lymph node by molecular probes is not sensitive enough to provide direct in vivo or peroperative imaging. At the time NIRF is performed on the excised specimen, high sensitivity imaging associated with spectral unmixing allowed such detection within less than 1 minute of examination.

Gold nanoflowers for 3D volumetric molecular imaging of tumors by photoacoustic tomography

By binding molecular probes that target tumor cells, gold nanoparticles （AuNPs） with superior characteristics have shown great potential in tumor molecular imaging studies. The non-invasive, high-resolution, and three-dimensional imaging of the targeted AuNPs within the tumor is desirable for both diagnosis and therapy. In this study, gold nanoflowers （AuNFs） are presented as a novel contrast agent for photoacoustic tomography （PAT）. By binding to folic acid, the molecular probe, the tail-vein injected AuNFs concentrated within the tumor site in mice; this was clearly visualized by three-dimensional （3D） PAT imaging. In addition, toxicity assay proved that AuNFs were harmless to living cells and animals. Our results demonstrate that AuNFs have great potential in tumor molecular imaging.

Label-Free Chemically and Molecularly Selective Magnetic Resonance Imaging

Biomedical imaging,especially molecular imaging,has been a driving force in scientific discovery,technological innovation,and precision medicine in the past two decades.While substantial advances and discoveries in chemical biology have been made to develop molecular imaging probes and tracers,translating these exogenous agents to clinical application in precision medicine is a major challenge.Among the clinically accepted imaging modalities,magnetic resonance imaging(MRI)and magnetic resonance spectroscopy(MRS)exemplify the most effective and robust biomedical imaging tools.Both MRI and MRS enable a broad range of chemical,biological diagnosis and characterization of many diseases and image-guided interventions.Using chemical,biological,and nuclear magnetic resonance properties of specific endogenous metabolites and native MRI contrast-enhancing biomolecules,label-free molecular and cellular imaging with MRI can be achieved in biomedical research and clinical management of patients with various diseases.This review article outlines the chemical and biological bases of several label-free chemically and molecularly selective MRI and MRS methods that have been applied in imaging biomarker discovery,preclinical investigation,and image-guided clinical management.Examples are provided to demonstrate strategies for using endogenous probes to report the molecular,metabolic,physiological,and functional events and processes in living systems,including patients.Future perspectives on label-free molecular MRI and its challenges as well as potential solutions,including the use of rational design and engineered approaches to develop chemical and biological imaging probes to facilitate or combine with label-free molecular MRI,are discussed.

Integrinα6 Targeted Near Infrared Fluorescent Imaging and Photoacoustic Imaging of Hepatocellular Carcinoma in Mice

Background and Aims:Hepatocellular carcinoma(HCC)is the fourth most common cause of cancer-related death and ranks sixth in terms of incident cases worldwide.The purpose of this study was to develop an effective and sensitive method to distinguish liver cancer tissues from normal tissues in HCC patients.Integrinα6 is a promising cell surface target for molecular imaging of HCC,where it is overexpressed and is a prognostic biomarker.We previously identified an integrinα6-targeted peptide CRWYDENAC(RWY)that has been used for positron emission tomography(PET)imaging of HCC in mouse models.Methods:We labeled the integrinα6-targeted RWY peptide with cyanine 7(Cy7)to form an optical probe(Cy7-RWY)for near infrared fluorescent(NIRF)and photoacoustic(PA)imaging in HCC.Mice transplanted with subcutaneous HCC-LM3 or orthotopic HCC-H22 cells that overexpressed integrinα6 were intravenously injected with Cy7-RWY and its corresponding Cy7-control.NIRF and PA images of mice were collected from 0 to 48 h after injection.Results:Both NIRF and PA signals started to accumulate in the tumor 2 h after injection of Cy7-RWY and peaked at 24 h.Conclusions:Cy7-RWY is a promising optical probe for NIRF and PA imaging of HCC in mice,and has potential clinical application for HCC detection.

Color-coded perfluorocarbon nanodroplets for multiplexed ultrasound and photoacoustic imaging

Laser-activated perfluorocarb on n anodroplets are an emerging class of phase-cha nge, dual-c ontrast age nts that can be utilized in ultraso und and photoacoustic imaging. Through the ability to differe ntiate subpopulations of nano droplets via laser activatio n at differe nt wavelengths of n ear-infrared light, optically-triggered color-coded perfluorocarb on nano droplets prese nt themselves as an attractive tool for multiplexed ultrasound and photoacoustic imaging. In particular, laser-activated droplets can be used to provide quantitative spatiotemporal information regarding distinct biological targets, allowing for their potential use in a wide range of diagnostic and therapeutic applications. In the work prese nted, laser-activated color-coded perfluorocarb on nan odroplets are syn thesized to selectively resp ond to laser irradiati on at corresp on ding wavele ngths. The dyn amic ultraso und and photoacoustic signals produced by laser-activated perfluorocarbon nano droplets are evaluated in situ prior to implementation in a murine model. In vivo, these particles are used to distinguish unique particle trafficking mechanisms and are show n to provide ultraso und and photoacoustic contrast for up to 72 hours within lymphatics. Overall, the con ducted studies show that laser-activated color-coded perfluorocarbo n nano droplets are a promising agent for multiplexed ultraso und and photoacoustic imaging.

A molecular probe carrying anti-tropomyosin 4 for early diagnosis of cerebral ischemia/reperfusion injury

In vivo imaging of cerebral ischemia/reperfusion injury remains an important challenge.We injected porous Ag/Au@SiO_(2) bimetallic hollow nanoshells carrying anti-tropomyosin 4 as a molecular probe into mice with cerebral ischemia/reperfusion injury and observed microvascular changes in the brain using photoacoustic imaging with ultrasonography.At each measured time point,the total photoacoustic signal was significantly higher on the affected side than on the healthy side.Twelve hours after reperfusion,cerebral perfusion on the affected side increased,cerebrovascular injury worsened,and anti-tropomyosin 4 expression increased.Twenty-four hours after reperfusion and later,perfusion on the affected side declined slowly and stabilized after 1 week;brain injury was also alleviated.Histopathological and immunohistochemical examinations confirmed the brain injury tissue changes.The nanoshell molecular probe carrying anti-tropomyosin 4 has potential for use in early diagnosis of cerebral ischemia/reperfusion injury and evaluating its progression.

用于深层组织分子成像的小型化光声/超声内窥成像探头

结直肠癌是全球癌症死亡的主要原因之一,常用的光学或超声消化道内镜仍然存在穿透深度低、对比度差、功能/分子成像能力不足等问题.本文介绍了一种小型化的手持式光声/超声双模态内窥探头,旨在克服现有技术在穿透深度和分子成像能力方面的限制.实验结果表明,该探头在组织12 mm深度下分别达到了345μm的光声横向分辨率和185μm的超声横向分辨率,并具有良好的对复杂结构目标成像的能力.本文还利用泵浦探测技术排除了血液背景的干扰,实现了肿瘤深层组织内亚甲基蓝分子的高特异性成像.这种小型化手持式光声/超声双模态内窥探头兼具大成像深度、高空间分辨和高特异性分子成像的特点,有望成为结直肠癌等消化道肿瘤诊断的重要工具,为早期诊断和治疗监测提供强有力的支持.

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。

生物医学光声成像技术及其临床应用进展

样品被短脉冲激光照射后会受激产生超声波,这种现象被称为光声效应。随着激光器技术及超声探测技术的进步,基于此效应的光声成像技术已成为生物医学成像领域发展最快的技术之一。光声成像作为一种混合型的成像方式,结合了光学成像的高对比度和光谱识别特性,以及超声成像大穿透深度下仍具备较高分辨率的特点。光声成像技术不仅可对包括血红蛋白、脂肪在内的多种组织成分进行高特异性成像,还能灵敏的反映包括血氧含量、氧代谢率等生理特征的变化,与超声技术的形态和结构成像具有很强的互补性,已在临床及生物医学研究领域体现出巨大的应用潜力。光声成像技术的这些特性使其在恶性肿瘤、心血管疾病、微循环异常等疾病的成像诊断和治疗引导中具有重要的应用前景。文章小结了本课题组在光声成像技术领域最近取得的一些新进展,包括利用解卷积技术进一步提高光声显微成像分辨率;利用压缩感知技术降低数据采集量,提高光声层析成像的速度;利用自制的纳米探针,实现光声分子成像和光热治疗。光声成像技术的这些进步使其在癌症、心脑血管疾病等方面的诊断和治疗更具有可行性,文章最后回顾了光声成像技术在乳腺癌、前哨淋巴结及血管内成像等方面的临床应用和研究进展。

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。

超声分子成像进展

超声分子成像是在超声医学成像的基础上,利用靶向超声造影剂为分子探针,以可视化和定量获取活体组织细胞的分子信息为目标的影像术。它不用进行手术活检,不仅可以给出病灶的空间信息,而且能确定它的性质,并可在低的临床风险下,实施针对性的治疗和对疗效进行评估。本文对现有的核医学分子成像,磁共振分子成像,光学分子成像和光声分子成像技术作了简单介绍,着重讨论了超声分子成像技术和应用的进展。

用于脑功能研究的生物光子学技术研究进展

脑成像技术是生物医学工程学研究的热点。现有传统脑成像手段,如X射线成像(X-ray)、磁共振成像(MRI)等已发展成熟,广泛应用于科学研究和临床诊疗。然而这些成像技术大多具有侵入性、设备体积庞大、成像成本高昂等局限性,且难以适用于特殊人群,如新生儿。该文介绍了几种可用于脑成像的微观光学分子成像模态,这些方法大多无创、成本较低且性能优异,具有广阔的发展前景。在给出了它们的成像原理、系统组成以及关键技术后,总结了已有的研究成果和现阶段研究进展。最后,通过列举和比较这几种成像模态的优缺点讨论了脑成像技术未来的发展方向。

聚多巴胺修饰的相变型对比剂的制备及体内外光声/超声显像

目的制备一种新型的聚多巴胺修饰的光声/超声双模态对比剂(PFP@PLGA@PDAs),探究其体内外光声、超声显影效果。方法①采用单乳化法一溶液氧化法合成聚多巴胺表面修饰的全氟正戊烷高分子纳米粒(PFP@PLGA@PDAs),检测PFP@PLGA@PDAs的基本性质;②以未修饰的相变型纳米粒(PFP@PLGAs)作为对照,应用琼脂糖模型测量纳米粒的体外光声和超声信号;③选取雌性BALB/c裸鼠(4~6周龄,体质量20g),构建裸鼠4T1乳腺癌动物模型,分为3组(PFP@PLGA@PDAs实验组,PFP@PLGAs对照组和PBS对照组,n=6),尾静脉注射对比剂后探究体内增强实体肿瘤的光声成像和超声成像的效果。结果@PFP@PLGA@PDAs悬液呈深褐色,纳米粒为球形的壳一核结构,粒径(209.40±36.15)nm,显微镜下见温度达43。C以上时发生液一气相变,CCK一8实验结果提示良好生物安全性。②体外光声成像显示,PFP@PLGA@PDAs的光声信号随浓度增加而明显增强(P<0.05),PFP@LGAs始终不显影;体外超声成像显示,经激光辐照后,PFP@PLGA@PDAs在基波和谐波模式下的回声信号均明显增强,不同辐照时长的谐波声强值间差异具有统计学意义(P<0.05),PFP@PLGAs的回声信号无明显变化。③体内光声成像显示,尾静脉注射PFP@PLGA@PDAs的荷瘤鼠的肿瘤部位在注射前和注射后1、4、24h的光声信号值分别为(0.12±0.03)、(0.22±0.04)、(0.67±0.08)、(0.37±0.06),差异有统计学意义(P<0.05),PFP@PLGAs和PBS组荷瘤鼠的肿瘤部位始终未见明显光声信号。体内超声成像显示,在激光辐照前,3组荷瘤鼠的肿瘤部位表现相似的超声回声信号,激光辐照后PFP@PLGA@PDAs组肿瘤的二维和造影图像均显示明显增多的点状高信号,而PFP@PLGAs和PBS组在辐照前后均未见明显回声信号改变。结论成功制备出一种聚多巴胺修饰的相变型对比剂,其具有作为一种分子探针实现肿瘤的体内外光声/超声双模态成像的潜力。