光声成像及其在生物医学中的应用

光声成像是一种新近迅速发展起来、基于生物组织内部光学吸收差异、以超声作媒介的无损生物光子成像方法,它结合了纯光学成像的高对比度特性和纯超声成像的高穿透深度特性的优点,以超声探测器探测光声波代替光学成像中的光子检测,从原理上避开了光学散射的影响,可以提供高对比度和高分辨率的组织影像,为研究生物组织的结构形态、生理特征、代谢功能、病理特征等提供了重要手段,在生物医学临床诊断以及在体组织结构和功能成像领域具有广泛的应用前景.对光声成像技术的机理、光声成像技术和方法、光声图像重建算法以及光声成像在生物医学上的应用情况作一个简单介绍,希望有助于推动我国在该领域的科研和开发应用工作的迅速发展.     

Nuclear morphology measurements with angle-resolved low coherence interferometry for application to cell biology and early cancer detection

The study of intact, living cells using non-invasive optical spectroscopic methods offers the opportunity to assess cellular structure and organization in a way that is not possible with commonly used cell biology imaging techniques. We have developed a novel spectroscopic technique for diagnosing disease at the cellular level based on using low-coherence interferometry (LCI) to detect the angular distribution of scattered light. Angle-resolved LCI (a/LCI) combines the ability of LCI to isolate scattering from sub-surface tissue layers with the ability of light scattering spectroscopy to obtain structural information on sub-wavelength scales. In application to examining cellular structure, a/LCI enables quantitative measurements of changes in the size and texture of cell nuclei. These quantitative measurements are characteristic of different pathological states. The capabilities of a/LCI were demonstrated using a clinical system that can be applied in endoscopic surveillance of esophageal tissue, producing high sensitivity and specificity for detecting dysplastic tissues in vivo. Experiments with in vitro cell samples also show the utility of a/LCI in observing structural changes due to environmental stimuli as well as detecting apoptosis due to chemotherapeutic agents.     

Use of Finite Difference Time Domain Simulations and Debye Theory for Modelling the Terahertz Reflection Response of Normal and Tumour Breast Tissue

The aim of this work was to evaluate the capabilities of Debye theory combined with Finite Difference Time Domain (FDTD) methods to simulate the terahertz (THz) response of breast tissues. Being able to accurately model breast tissues in the THz regime would facilitate the understanding of image contrast parameters used in THz imaging of breast cancer. As a test case, the model was first validated using liquid water and simulated reflection pulses were compared to experimental measured pulses with very good agreement (p = 1.00). The responses of normal and cancerous breast tissues were simulated with Debye properties and the correlation with measured data was still high for tumour (p = 0.98) and less so for normal breast (p = 0.82). Sections of the time domain pulses showed clear differences that were also evident in the comparison of pulse parameter values. These deviations may arise from the presence of adipose and other inhomogeneities in the breast tissue that are not accounted for when using the Debye model. In conclusion, the study demonstrates the power of the model for simulating THz reflection imaging; however, for biological tissues extra Debye terms or a more detailed theory may be required to link THz image contrast to physiological composition and structural changes of breast tissue associated with differences between normal and tumour tissues.     

Strongly Magnetic Iron Nanoparticles Improve the Diagnosis of Small Tumours in the Reticuloendothelial System by Magnetic Resonance Imaging

Despite advances in non-invasive medical imaging, accurate nodal staging of malignancy continues to rely on surgery. Superparamagnetic iron oxide nanoparticles (IONP) with lymphotropic qualities have shown some promise as contrast agents for MRI of the lymph nodes, but recent large-scale studies failed to show consistent detection of tumours below 5 mm. Herein we compare imaging of splenic and lymph node tissue using iron/iron oxide core/shell nanoparticles (Fe NP) that have superior magnetic qualities to IONP, to determine whether improved negative contrast in T₂-weighted MRI can enhance the diagnosis of small tumours in the reticuloendothelial system. To provide an in vivo pre-clinical model of human lymph node micrometastases, breast cancer cells were injected into the spleens of mice, providing localised areas of tumour growth. MR images of groups of tumour-bearing and sham-treated animals were generated using a 1.5 T imaging system and analysed by two independent, blinded radiologists. Fe NP improved the sensitivity and specificity of MRI when compared to IONP, enabling accurate detection of tumours as small as 1–3 mm. The use of Fe NP as contrast agents have the potential to improve the diagnostic accuracy of MRI in cancer patients, leading to more rapid and effective treatment.     

Advances in using MRI probes and sensors for in vivo cell tracking as applied to regenerative medicine

The field of molecular and cellular imaging allows molecules and cells to be visualized in vivo non-invasively. It has uses not only as a research tool but in clinical settings as well, for example in monitoring cell-based regenerative therapies, in which cells are transplanted to replace degenerating or damaged tissues, or to restore a physiological function. The success of such cell-based therapies depends on several critical issues, including the route and accuracy of cell transplantation, the fate of cells after transplantation, and the interaction of engrafted cells with the host microenvironment. To assess these issues, it is necessary to monitor transplanted cells non-invasively in real-time. Magnetic resonance imaging (MRI) is a tool uniquely suited to this task, given its ability to image deep inside tissue with high temporal resolution and sensitivity. Extraordinary efforts have recently been made to improve cellular MRI as applied to regenerative medicine, by developing more advanced contrast agents for use as probes and sensors. These advances enable the non-invasive monitoring of cell fate and, more recently, that of the different cellular functions of living cells, such as their enzymatic activity and gene expression, as well as their time point of cell death. We present here a review of recent advancements in the development of these probes and sensors, and of their functioning, applications and limitations.KEY WORDS: Regenerative medicine, Stem cells, Magnetic resonance imaging, Paramagnetic contrast agents, CEST, Perfluorocarbon particles, Biosensor, Cell labeling, Cellular function     

Design of a Modular Protein-Based MRI Contrast Agent for Targeted Application

Magnetic resonance imaging (MRI) offers a non-radioactive alternative for the non-invasive detection of tumours. Low molecular weight MRI contrast agents currently in clinical use suffer either from a lack of specificity for tumour tissue or from low relaxivity and thus low contrast amplification. In this study, we present the newly designed two domain fusion protein Zarvin, which is able to bind to therapeutic IgG antibodies suitable for targeting, while facilitating contrast enhancement through high affinity binding sites for Gd³⁺. We show that the Zarvin fold is stable under serum conditions, specifically targets a cancer cell-line when bound to the Cetuximab IgG, and allows for imaging with high relaxivity, a property that would be advantageous for the detection of small tumours and metastases at 1.5 or 3 T.     

多功能磁共振造影剂研究进展

磁共振成像技术因对人体无创、任意方向断层扫描三维图像且分辨率较高、提供形态与功能两方面诊断评价等突出优点,成为了临床上用于疾病诊断的重要手段之一。临床上使用磁共振造影剂可以提高成像的分辨率和灵敏度,提高图像质量,增强对比度和可读性。但是,各种成像技术由于实现原理不同,具有各自的优势和缺陷,靠传统单一的诊断模式无法提供疾病的全面信息,因而在对各种复杂疾病进行诊断时会受到一定的限制。因此,将磁共振成像与其他成像技术如CT成像、超声成像等联合起来使用,则可以达到优势互补的效果,能为疾病的临床诊断提供更快捷精确的信息,同时可将磁共振成像与各种治疗方式结合在一起,即开发基于磁共振成像的诊断治疗一体化试剂,以实现对疾病的即时治疗和实时监控。本文主要介绍了磁共振成像造影剂的原理和种类,并且综述了目前国内外在基于磁共振成像的多功能造影剂/诊疗制剂这一领域的研究进展,最后就未来可能的研究方向进行了展望。     

热声成像技术及其在生物医学中的研究进展

摘要：成像技术在疾病的诊断、治疗和监测中起着重要的作用。热声成像作为一种非电离和非侵入性的新型生物医学成像技术,结合了微波成像高对比度和超声成像高分辨率的优点。因其具有利用内源性对比剂（如水和离子）或多种外源性对比剂（或两者兼有）提供结构、功能、和分子信息的能力,在预临床和临床应用中显示出了巨大的潜力。近几十年来,由于微波辐射源和超声硬件的不断发展,热声成像技术已被广泛用于生物医学成像领域。本文阐述了热声成像的基本原理及成像特点,介绍了近年来热声成像技术在生物医学上的应用、当前在解决相应临床问题应用中的优势及研究现状,最后针对热声成像技术在现有生物医学中面临的挑战对该技术进行了展望。     

Multimodal Raman spectroscopy and optical coherence tomography for biomedical analysis

Optical techniques hold great potential to detect and monitor disease states as they are a fast, non-invasive toolkit. Raman spectroscopy (RS) in particular is a powerful label-free method capable of quantifying the biomolecular content of tissues. Still, spontaneous Raman scattering lacks information about tissue morphology due to its inability to rapidly assess a large field of view. Optical Coherence Tomography (OCT) is an interferometric optical method capable of fast, depth-resolved imaging of tissue morphology, but lacks detailed molecular contrast. In many cases, pairing label-free techniques into multimodal systems allows for a more diverse field of applications. Integrating RS and OCT into a single instrument allows for both structural imaging and biochemical interrogation of tissues and therefore offers a more comprehensive means for clinical diagnosis. This review summarizes the efforts made to date toward combining spontaneous RS-OCT instrumentation for biomedical analysis, including insights into primary design considerations and data interpretation.     

Molecular magnetic resonance imaging with targeted contrast agents

Magnetic resonance imaging (MRI) produces high-resolution three-dimensional maps delineating morphological features of the specimen. Differential contrast in soft tissues depends on endogenous differences in water content, relaxation times, and/or diffusion characteristics of the tissue of interest. The specificity of MRI can be further increased by exogenous contrast agents (CA) such as gadolinium chelates, which have been successfully used for imaging of hemodynamic parameters including blood perfusion and vascular permeability. Development of targeted MR CA directed to specific molecular entities could dramatically expand the range of MR applications by combining the noninvasiveness and high spatial resolution of MRI with specific localization of molecular targets. However, due to the intrinsically low sensitivity of MRI (in comparison with nuclear imaging), high local concentrations of the CA at the target site are required to generate detectable MR contrast. To meet these requirements, the MR targeted CA should recognize targeted cells with high affinity and specificity. They should also be characterized by high relaxivity, which for a wide variety of CA depends on the number of contrast-generating groups per single molecule of the agent. We will review different designs and applications of targeted MR CA and will discuss feasibility of these approaches for in vivo MRI.     

超声分子成像的研究进展

超声成像无创、无放射性、低成本、实时成像的优点,使其成为目前世界上应用最广的成像手段之一。特别是超声造影剂引入之后,超声成像的图像分辨率和灵敏度得到了大大提高,使超声成像在临床上得到了进一步应用。近年来,随着分子生物学和超声成像技术的不断发展,人们提出了＂超声分子成像＂的概念。它是一项结合了分子靶向造影剂和超声影像技术的能在分子水平下观察病理变化的新兴技术,目前这一技术还处于研究初期阶段。但大量临床前的研究成果已表明超声分子成像在诊断血管生成、炎症和血栓三种疾病具有很大应用前景。本文主要综述了目前常用超声造影剂的种类以及超声分子成像技术的研究现状,并对该技术进行了讨论和展望。     

超声分子成像的研究进展

超声成像无创、无放射性、低成本、实时成像的优点,使其成为目前世界上应用最广的成像手段之一。特别是超声造影剂引入之后,超声成像的图像分辨率和灵敏度得到了大大提高,使超声成像在临床上得到了进一步应用。近年来,随着分子生物学和超声成像技术的不断发展,人们提出了"超声分子成像"的概念。它是一项结合了分子靶向造影剂和超声影像技术的能在分子水平下观察病理变化的新兴技术,目前这一技术还处于研究初期阶段。但大量临床前的研究成果已表明超声分子成像在诊断血管生成、炎症和血栓三种疾病具有很大应用前景。本文主要综述了目前常用超声造影剂的种类以及超声分子成像技术的研究现状,并对该技术进行了讨论和展望。     

Development of high-sensitivity near-infrared fluorescence imaging device for early cancer detection

We have developed a high-sensitivity near-infrared (NIR) optical imaging system for noninvasive cancer detection based on the molecular-labeled fluorescent contrast agents. Recent developments in molecular beacons offer a way to selectively tag various precancer and cancer signatures and provide high tumor-to-background contrast. Near-infrared imaging can deeply probe tissue up to a couple of centimeters; thus, it possesses the potential for noninvasive detection of breast or lymph node cancer. A phase cancellation (in- and antiphase) device is used to increase the sensitivity in detecting fluorescent photons and the accuracy of tumor localization. The optoelectronic system consists of the laser diode sources, fiber optics, interference filter (to select the fluorescent photons), and the high-sensitivity photon detector (photomultiplier tube). The source-detector pair scans the tissue surface in multiple directions, and the localization image can be obtained by angular back-projection reconstruction. Simulations and experimental data demonstrated the feasibility of detection and localization offluorescent object embedded inside the highly scattering media. Tumor-bearing mouse model with injection of fluorescent contrast agents is used to simulate the human breast tumor labeled with molecular beacons. The system can detect fluorescent contrast agents as small as one nanomole at the depth of three centimeters, with a three-millimeter localization error. This instrument has the potential for tumor diagnosis and imaging, and the accuracy of the localization suggests that this system could help guide the clinical fine-needle biopsy. Also, this portable device would be complementary to x-ray mammography and provide add-on information on early diagnosis and localization of breast tumor.     

Galvanic apparent internal impedance: An intrinsic tissue property

Using basic galvanic cell principles, the ability of tissues to generate electrical current through electrolysis was characterized. Studying Zn/Cu electrolysis in animal organs revealed a fundamental and measurable tissue-specific property - the galvanic apparent internal impedance (GAII), that is most likely related to the salt bridge function of tissues delineated by electrodes. Further to the fundamental knowledge acquired, GAII enables a new diagnostic method to distinguish between tissue types and to determine their health status without a need for expensive calibration, as often required when external power source is used. We demonstrated the GAII sensitivity in detecting tissue ablation with microwave heating or irreversible electroporation. The results open the way for a novel, inexpensive self-powered tissue diagnostic system for a wide range of applications such as minimally invasive tissue health status, ischemia, hydration, real time intra-operative control of minimally invasive surgery, medical imaging, virtual biopsy and many others.     

Safe common agents for improved NMR contrast

As nuclear magnetic resonance imaging techniques have developed, a need for agents which can enhance and improve the natural tissue relaxation time differences has become apparent. Especially valuable would be agents that differentially alter NMR images in a manner related to tissue physiology and disease processes. Sophisticated para-magnetic and free radical contrast agents will be discussed in other papers in this issue. However, in this report, some common agents which are currently used in research and in human clinical studies for other purposes, but which can alter NMR contrast will be discussed. These agents include olive oil, estrogen hormones, diuretics, ethanol, glycerin, and dimethyl sulfoxide. Measurements of their relative effects on T1 and T2 of normal and cancerous breast tissues, a variety of body organs, and brain are presented. Some of these agents may have immediate practical applications in human NMR imaging studies.     

The Applicability of TaqMan-Based Quantitative Real-Time PCR Assays for Detecting and Enumerating Cryptosporidium spp. Oocysts in the Environment

Quantitative real-time polymerase chain reaction (qPCR) assays to detect Cryptosporidium oocysts in clinical samples are increasingly being used to diagnose human cryptosporidiosis, but a parallel approach for detecting and identifying Cryptosporidium oocyst contamination in surface water sources has yet to be established for current drinking water quality monitoring practices. It has been proposed that Cryptosporidium qPCR-based assays could be used as viable alternatives to current microscopic-based detection methods to quantify levels of oocysts in drinking water sources; however, data on specificity, analytical sensitivity, and the ability to accurately quantify low levels of oocysts are limited. The purpose of this study was to provide a comprehensive evaluation of TaqMan-based qPCR assays, which were developed for either clinical or environmental investigations, for detecting Cryptosporidium oocyst contamination in water. Ten different qPCR assays, six previously published and four developed in this study were analyzed for specificity and analytical sensitivity. Specificity varied between all ten assays, and in one particular assay, which targeted the Cryptosporidium 18S rRNA gene, successfully detected all Cryptosporidium spp. tested, but also cross-amplified T. gondii, fungi, algae, and dinoflagellates. When evaluating the analytical sensitivity of these qPCR assays, results showed that eight of the assays could reliably detect ten flow-sorted oocysts in reagent water or environmental matrix. This study revealed that while a qPCR-based detection assay can be useful for detecting and differentiating different Cryptosporidium species in environmental samples, it cannot accurately measure low levels of oocysts that are typically found in drinking water sources.     

In vivo cytometry: a spectrum of possibilities.

BACKGROUND: We investigate whether optical imaging can reliably detect abnormalities in tissue, in a range of specimens (live cells in vitro; fixed, fresh ex-vivo and in vivo tissue), without the use of added contrast agents, and review our promising spectral methods for achieving quantitative, real-time, high resolution intrasurgical optical diagnostics. METHODS: We use reflectance, fluorescence, two-photon, and Mie scattering imaging, performed with instrumentation we developed or modified, to detect intrinsic tissue signatures. Emphasis is on spectral/hyperspectral imaging approaches allowing the equivalent of in vivo pathology. RESULTS: With experimental focus on unstained specimens, we demonstrate the ability to segment tissue images for cancer detection. Spectral reflectance imaging, coupled with advanced analysis, typically yields 90% specificity and sensitivity. Autofluorescence is also shown to be diagnostically useful, with lymph nodes results highlighted here. Elastic scattering hyperspectral imaging endoscopy, using a new instrument we designed and built, shows promise in bronchoscopic detection of dysplasia and early cancer in patients. CONCLUSIONS: The results demonstrate that advanced optical imaging can detect and localize cellular signatures of cancer in real-time, in vivo, without the use of contrast agents, in animals and humans. This is an important step towards tight spatio-temporal coupling between such detection and clinical intervention.     

研究报告: 小动物高分辨扩散磁共振成像数据分析方法

扩散磁共振成像(dMRI)是一种非侵入性的、能提供生物体内水分子扩散运动相关信息的成像技术,可用于检测神经纤维微观结构的变化．dMRI的出现为大脑结构与功能研究提供了全新的检测手段．过去的20年中,dMRI在实验方法和临床应用上均取得了重大进展．然而dMRI应用在基于动物模型的临床前脑成像研究中却并不常见．本文针对dMRI在临床前脑成像研究中的应用,建立了系列针对小动物高分辨dMRI数据的分析方法：a．构建了大鼠高分辨dMRI图像模板;b．实现了适用于小动物研究的基于体素的统计分析(VBA)方法与基于纤维束的空间统计分析(TBSS)方法;c．实现了小动物脑白质纤维束的确定性与概率性跟踪．这些方法的实现不仅能为小动物脑dMRI研究提供统一的图像模板与完善的计算方法,还将大大促进dMRI技术在小动物脑成像研究中的应用．     

Monoclonal Antibody-Based Dipstick Assay: A Reliable Field Applicable Technique for Diagnosis of Schistosoma mansoni Infection Using Human Serum and Urine Samples

A field applicable diagnostic technique, the dipstick assay, was evaluated for its sensitivity and specificity in diagnosing human Schistosoma mansoni infection. A monoclonal antibody (mAb) against S. mansoni adult worm tegumental antigen (AWTA) was employed in dipstick and sandwich ELISA for detection of circulating schistosome antigen (CSA) in both serum and urine samples. Based on clinical and parasitological examinations, 60 S. mansoni-infected patients, 30 patients infected with parasites other than schistosomiasis, and 30 uninfected healthy individuals were selected. The sensitivity and specificity of dipstick assay in urine samples were 86.7% and 90.0%, respectively, compared to 90.0% sensitivity and 91.7% specificity of sandwich ELISA. In serum samples, the sensitivity and specificity were 88.3% and 91.7% for dipstick assay vs. 91.7% and 95.0% for sandwich ELISA, respectively. The diagnostic efficacy of dipstick assay in urine and serum samples was 88.3% and 90.0%, while it was 90.8% and 93.3% for sandwich ELISA, respectively. The diagnostic indices of dipstick assay and ELISA either in serum or in urine were statistically comparable (P>0.05). In conclusion, the dipstick assay offers an alternative simple, rapid, non-invasive technique in detecting CSA or complement to stool examinations especially in field studies.     

Visualization of the enzymatic activity in living systems using activated NMR contrast agents

New approaches to the development and some applications of novel paramagnetic "sensing" contrast agents designed for specific visualization of the enzymatic activity in living systems are reviewed. The activation of the above sensing agents includes either the cleavage or the synthesis of reactive precursor compounds that recombine with macromolecules with the formation of immobilized or rotationally inhibited paramagnetic cations. This effect results in strong changes of water proton relaxivity. The need in such agents is justified by efforts to utilize magnetic resonance imaging (MRI) for the visualization of fine structures in the living tissue as well as for increasing the molecular specificity of MRI. The review also contains information regarding recent efforts of increasing the sensitivity of MRI to the presence of paramagnetic cations in living systems.