Fluorescence imaging with near-infrared light: new technological advances that enable in vivo molecular imaging

A recent development in biomedical imaging is the non-invasive mapping of molecular events in intact tissues using fluorescence. Underpinning to this development is the discovery of bio-compatible, specific fluorescent probes and proteins and the development of highly sensitive imaging technologies for in vivo fluorescent detection. Of particular interest are fluorochromes that emit in the near infrared (NIR), a spectral window, whereas hemoglobin and water absorb minimally so as to allow photons to penetrate for several centimetres in tissue. In this review article we concentrate on optical imaging technologies used for non-invasive imaging of the distribution of such probes. We illuminate the advantages and limitations of simple photographic methods and turn our attention to fluorescence-mediated molecular tomography (FMT), a technique that can three-dimensionally image gene expression by resolving fluorescence activation in deep tissues. We describe theoretical specifics, and we provide insight into its in vivo capacity and the sensitivity achieved. Finally, we discuss its clinical feasibility. Electronic Publication     

Optical-based molecular imaging: contrast agents and potential medical applications

Laser- and sensitive charge-coupled device technology together with advanced mathematical modelling of photon propagation in tissue has prompted the development of novel optical imaging technologies. Fast surface-weighted imaging modalities, such as fluorescence reflectance imaging (FRI) and 3D quantitative fluorescence-mediated tomography have now become available [1, 2]. These technical advances are paralleled by a rapid development of a whole range of new optical contrasting strategies, which are designed to generate molecular contrast within a living organism. The combination of both, technical advances of light detection and the refinement of optical contrast media, finally yields a new spectrum of tools for in vivo molecular diagnostics. Whereas the technical aspects of optical imaging are covered in more detail in a previous review article in "European Radiology" [3], this article focuses on new developments in optical contrasting strategies and design of optical contrast agents for in vivo diagnostics. Electronic Publication     

In Vivo Cell Tracking with Bioluminescence Imaging

Molecular imaging is a fast growing biomedical research that allows the visual representation, characterization and quantification of biological processes at the cellular and subcellular levels within intact living organisms. In vivo tracking of cells is an indispensable technology for development and optimization of cell therapy for replacement or renewal of damaged or diseased tissue using transplanted cells, often autologous cells. With outstanding advantages of bioluminescence imaging, the imaging approach is most commonly applied for in vivo monitoring of transplanted stem cells or immune cells in order to assess viability of administered cells with therapeutic efficacy in preclinical small animal models. In this review, a general overview of bioluminescence is provided and recent updates of in vivo cell tracking using the bioluminescence signal are discussed.

     

Optical imaging of experimental arthritis using allogeneic leukocytes labeled with a near-infrared fluorescent probe

Purpose The purpose of this study was to assess the feasibility of inflammation detection in an antigen-induced arthritis model using fluorescent leukocytes and optical imaging. Methods Antigen-mediated monoarthritis was induced in the right knee of 12 Sprague-Dawley rats. Six rats remained untreated and six rats were treated with cortisone. All rats received ex vivo fluorescent-labeled rat leukocytes. Optical images of both knees were acquired before and at 5 min, 1 h, 4 h, and 24 h after cell injection. Images were evaluated qualitatively and quantitatively by calculating signal intensity ratios between the right arthritic (A) and contralateral normal (N) knee. A/N ratios were tested for significant differences between baseline values and values after cell injection using a paired t test as well as between the untreated and cortisone-treated group using an unpaired t test. Synovial specimens were processed and evaluated for labeled cells with fluorescence microscopy. Results At 4 h and 24 h p.i., the A/N ratios of untreated arthritic knees showed a significant signal increase compared with baseline values (p<0.05) and a significant difference compared with A/N ratios of cortisone-treated animals (p<0.05). Fluorescent microscopy confirmed the presence of labeled cells in the arthritic synovium. Conclusion Inflammation in antigen-induced arthritis can be detected with ex vivo labeled allogenic leukocytes and optical imaging.     

Cell tracking with gadophrin-2: a bifunctional contrast agent for MR imaging,optical imaging,and fluorescence microscopy

The purpose of this study was to assess the feasibility of use of gadophrin-2 to trace intravenously injected human hematopoietic cells in athymic mice, employing magnetic resonance (MR) imaging, optical imaging (OI), and fluorescence microscopy. Mononuclear peripheral blood cells from GCSF-primed patients were labeled with gadophrin-2 (Schering AG, Berlin, Germany), a paramagnetic and fluorescent metalloporphyrin, using established transfection techniques with cationic liposomes. The labeled cells were evaluated in vitro with electron microscopy and inductively coupled plasma atomic emission spectrometry. Then, 1×10⁶–3×10⁸ labeled cells were injected into 14 nude Balb/c mice and the in vivo cell distribution was evaluated with MR imaging and OI before and 4, 24, and 48 h after intravenous injection (p.i.). Five additional mice served as controls: three mice were untreated controls and two mice were investigated after injection of unlabeled cells. The contrast agent effect was determined quantitatively for MR imaging by calculating signal-to-noise-ratio (SNR) data. After completion of in vivo imaging studies, fluorescence microscopy of excised organs was performed. Intracellular cytoplasmatic uptake of gadophrin-2 was confirmed by electron microscopy. Spectrometry determined an uptake of 31.56 nmol Gd per 10⁶ cells. After intravenous injection, the distribution of gadophrin-2 labeled cells in nude mice could be visualized by MR, OI, and fluorescence microscopy. At 4 h p.i., the transplanted cells mainly distributed to lung, liver, and spleen, and 24 h p.i. they also distributed to the bone marrow. Fluorescence microscopy confirmed the distribution of gadophrin-2 labeled cells to these target organs. Gadophrin-2 is suited as a bifunctional contrast agent for MR imaging, OI, and fluorescence microscopy and may be used to combine the advantages of each individual imaging modality for in vivo tracking of intravenously injected hematopoietic cells.     

Contrast agents for optical mammography

Summary Near infrared imaging is a non-invasive imaging modality which uses light of a spectral range between 650 and 1000 nm for tissue transillumination. Near infrared photons can penetrate by diffusion into tissue up to several centimeters due to low absorption by intrinsic chromophors (e. g. hemoglobine). During the last years optical mammography has become field of growing interest. Several prototypes of near infrared scanners have been developed for clinical studies in order to obtain transillumination images of the breast. The results indicated, that discrimination of tumors located up to several centimeters below the tissue surface (e. g. breast tumors) from surrounding healthy tissue did not succeed with sufficient specificity. The diagnostic potential of near infrared imaging can be enhanced using dyes as contrast agents. Specially designed cyanine dye derivatives are potential contrast agents because of their suitable optical properties and pharmacokinetic behaviour leading to an increased tumor fluorescence in animals after intravenous injection.      

临床用肿瘤细胞凋亡核医学显像剂研究进展

凋亡在肿瘤的发生、发展和治疗中发挥重要的作用,因此无创、动态监测凋亡已成为目前抗肿瘤治疗的研究热点。目前已有靶向外翻细胞膜磷脂显像剂99Tcm-4,5-2（硫代乙酰胺）戊酰-膜联蛋白V和99Tcm-联肼尼克酰胺-膜联蛋白V、靶向半胱天冬酶（caspases）显像剂18F-ICMT-11和18F-CP18、靶向凋亡细胞膜印迹显像剂18F-ML-10进入临床试验阶段,虽然它们存在局限性,但当与传统的成像手段比较时,它们在肿瘤的诊断、治疗监测上具备一定的优越性。因此,肿瘤凋亡显像剂具有广泛的应用前景。笔者就目前核医学肿瘤细胞凋亡显像剂在肿瘤诊疗中的研究进展进行综述。     

光学成像示踪细胞

因光具适应性、灵敏性、分辨率和无创性,其作为科学研究工具由来已久,也是光学成像(optical imaging,OI的基础。光学成像包括多种成像技术及方法,具有成像快速     

细胞磁共振成像技术在体示踪免疫细胞的研究进展

肿瘤免疫治疗是继手术、放疗和化疗后出现的一种新的治疗方法。在体示踪免疫细胞有助于指导肿瘤的免疫治疗并预测和评估其治疗效果。细胞磁共振成像技术运用特殊的对比剂,能够无创、实时、可重复地监测体内细胞的活动。近年来,研究者对应用细胞磁共振成像技术在体示踪免疫细胞进行了大量的研究并取得了一定的进展,该文将就这一研究进展作一综述。     

干细胞移植的磁性标记及磁共振成像活体示踪

干细胞移植的临床应用需要解决植入活体内干细胞在体内存活、迁移及分化的监测问题。通过对干细胞进行顺磁性标记,磁共振成像(MRI)能够在活体上显示标记的干细胞,并进行特异性地追踪及定位,是目前干细胞活体示踪极具前景的方法。干细胞进行磁性标记主要利用铁类或钆类对比剂,两者各有优缺点。利用铁类或钆类对比剂标记干细胞并进行MRI活体监测取得了成功。并在心脑缺血损伤的疾病模型中得到应用,但在干细胞磁性标记的载体选用及其标记率、标记的持久性、标记对细胞活力及遗传性状方面尚存在一定的问题。     

细胞示踪影像学技术的发展

随着细胞治疗的不断深入,采取有效的活体细胞示踪技术评价细胞治疗后的疗效并监测移植细胞的分化增殖、迁移及生存状况,对细胞治疗后脏器功能改善机制的深入研究及指导未来细胞治疗的临床应用显得尤为重要,因此活体细胞示踪成像技术成为细胞治疗由基础研究到临床应用推广的关键技术之一.笔者主要就当前细胞示踪影像技术(主要是MRI及光学成像)的发展及其可行性作一综述.     

裸鼠胃癌移植瘤的近红外荧光成像

目的：通过对非特异性探针Cy5.5在裸鼠体内分布及显像研究,探讨近红外荧光成像对胃癌的早期诊断及动态监测价值。方法：用MGC-803细胞株建立胃癌动物模型,进行早期、实时活体及离体显像实验。结果：近红外荧光成像可检测早期胃癌移植瘤的平均大小为2.807mm×3.045mm,与游标卡尺测得的肿瘤大小呈直线相关,r=0.924,P〈0.05。Cy5.5主要分布在肿瘤组织,主要代谢器官为肾脏;注入探针30min后,裸鼠肿瘤部位成像清晰,荧光寿命、荧光强度均高于对照部位（P〈0.05）。60min后,肿瘤区的荧光强度始高于血液（P〈0.05）。90min时达峰值。肿瘤部位的平均荧光寿命为（3.1376±0.9894）ns,明显高于对侧部位（P〈0.05）。结论：近红外荧光成像可用于胃癌的早期诊断及瘤体的动态监测。     

脑卒中细胞凋亡的活体成像进展

脑卒中是全球第二大常见死因,是我国第一大死亡和致残原因.缺血脑卒中急性期及迟发性神经元死亡期均存在神经元细胞的凋亡,凋亡决定了脑卒中最终的梗死体积.应用活体成像技术能够无创地检测脑内的细胞凋亡信息,为脑卒中的早期诊断、病程及治疗效果监测提供了新的方向.     

In vivo tracking of genetically engineered, anti-HER2/neu directed natural killer cells to HER2/neu positive mammary tumors with magnetic resonance imaging

The purpose of this study is to optimize labeling of the human natural killer (NK) cell line NK-92 with iron-oxide-based contrast agents and to monitor the in vivo distribution of genetically engineered NK-92 cells, which are directed against HER2/neu receptors, to HER2/neu positive mammary tumors with magnetic resonance (MR) imaging. Parental NK-92 cells and genetically modified HER2/neu specific NK-92-scFv(FRP5)-zeta cells, expressing a chimeric antigen receptor specific to the tumor-associated ErbB2 (HER2/neu) antigen, were labeled with ferumoxides and ferucarbotran using simple incubation, lipofection and electroporation techniques. Labeling efficiency was evaluated by MR imaging, Prussian blue stains and spectrometry. Subsequently, ferucarbotran-labeled NK-92-scFv(FRP5)-zeta (n=3) or parental NK-92 cells were intravenously injected into the tail vein of six mice with HER2/neu-positive NIH 3T3 mammary tumors, implanted in the mammary fat pad. The accumulation of the cells in the tumors was monitored by MR imaging before and 12 and 24 h after cell injection (p.i.). MR data were correlated with histopathology. Both the parental NK-92 and the genetically modified NK-92-scFv(FRP5)-zeta cells could be labeled with ferucarbotran and ferumoxides by lipofection and electroporation, but not by simple incubation. The intracellular cytoplasmatic iron-oxide uptake was significantly higher after labeling with ferucarbotran than ferumoxides (P<0.05). After intravenous injection of 5×10⁶ NK-92-scFv(FRP5)-zeta cells into tumor-bearing mice, MR showed a progressive signal decline in HER2/neu-positive mammary tumors at 12 and 24 h (p.i.). Conversely, injection of 5×10⁶ parental NK-92 control cells, not directed against HER2/neu receptors, did not cause significant signal intensity changes of the tumors. Histopathology confirmed an accumulation of the former, but not the latter cells in tumor tissue. The human natural killer cell line NK-92 can be efficiently labeled with clinically applicable iron-oxide contrast agents, and the accumulation of these labeled cells in murine tumors can be monitored in vivo with MR imaging. This MR cell tracking technique may be applied to monitor NK-cell based immunotherapies in patients in order to assess the presence and extent of NK-cell tumor accumulations and, thus, to determine therapy response early and non-invasively.     

光学成像与核素显像手术导航的研究进展

手术彻底切除病灶是提高肿瘤治疗效果及改善预后的关键。光学成像与核素显像灵敏度与分辨率高,能直观准确显示肿瘤的位置与范围,精确指导手术切除,是肿瘤术中导航的有效方法。随着肿瘤特异性探针的不断出现,导航仪器的不断改进,以及集核素显像与光学成像特点于一体的切伦科夫显像等新技术的涌现,核素显像及光学成像的术中导航在指导肿瘤手术切除中发挥着愈发重要的作用。     

分子成像技术的研究进展

分子成像是新时代的医学成像,它可以无创性监测活体内的细胞和分子水平的生物学过程,其中包括核医学分子显像、磁共振分子成像、超声分子成像、光学分子成像和X射线分子成像等.目前,由于多学科融合的发展,多模式融合成像技术已成功用于临床,如PET-CT和PET-MRI.随着分子探针的发展和多模式融合成像技术的成熟,越来越多的分子...     

核医学分子影像技术在外泌体活体示踪中的研究进展

外泌体是参与细胞间信号传导的重要物质,具有很高的生物学价值,目前已成为研究热点。高特异性、高灵敏度的外泌体示踪方法是揭示外泌体生物学功能的关键。外泌体示踪主要依靠分子影像学技术,其优势主要集中在核医学分子显像,其中包括外泌体的核素直接标记法和间接标记法。核医学分子显像可与解剖学成像相结合,定量监测外泌体的分布,还可对外泌体治疗的效果进行评价,在外泌体示踪研究中发挥着极其重要的作用。笔者将从外泌体的生物学价值、核医学分子影像技术在外泌体示踪中的研究进展作一综述。     

Real-time catheter tracking and adaptive imaging

PURPOSE: To evaluate the performance of a real-time MR system for interventional procedures that adjusts specific image parameters in real time based on a catheter's speed of insertion. MATERIALS AND METHODS: The system was implemented using only the hardware provided with a standard short-bore 1.5 T scanner (Siemens Magnetom Sonata) (with the exception of small tracking markers affixed to the catheter). The system tracks the position of an MR microcoil-instrumented catheter and automatically updates the scan plane's position and orientation, as well as other features, including, but not limited to, field of view, resolution, tip angle, and TE. A real-time feedback loop continuously localizes the tracking markers, updates the scan plane position and orientation, calculates the catheter's speed, adjusts the value of specific image parameters, then collects new image data, reconstructs an image, and provides it for immediate display. The system was evaluated in phantom and in vivo porcine experiments. RESULTS: The system is able to accurately localize a moving catheter in the abdominal aorta, calculate the device speed, and respond by adjusting specified image parameters 98% of the time, with precision of approximately 2 mm and 1.5 degrees. CONCLUSION: Simply slowing the speed of the catheter allows the clinician to adjust predetermined image parameters. This work also has the potential to build a degree of intelligence into the scanner, enabling it to react to changes in the clinical environment and automatically optimize specific image parameters.     

斑点追踪成像技术评价尿毒症患者左心室功能

目的探讨斑点追踪成像技术(STI)评价尿毒症患者左心室功能的意义。方法对49例尿毒症患者测量其常规超声心动指标,并用STI技术检测左室基底部及心尖段的扭转角度及解旋角度,另取40名健康志愿者进行对照。结果尿毒症患者E/A值、基底部与心尖部心肌节段扭转及解旋角度较对照组均降低(P均<0.05),左室内径、室壁厚度较对照组增加(P均<0.05),左室射血分数(LVEF)的变化无统计学意义(P>0.05)。结论尿毒症患者心肌节段扭转及解旋角度减低,二维STI技术可定量评价尿毒症患者左室心肌功能的变化。     

Advantages and limitations of prospective head motion compensation for MRI using an optical motion tracking device

RATIONALE AND OBJECTIVES: Subject motion appears to be a limiting factor in numerous magnetic resonance (MR) imaging (MRI) applications. In particular, head tremor, which often accompanies stroke, may render certain high-resolution two- (2D) and three-dimensional (3D) techniques inapplicable. The reason for that is head movement during acquisition. The study objective is to achieve a method able to compensate for complete motion during data acquisition. The method should be usable for every sequence and easily implemented on different MR scanners. MATERIALS AND METHODS: The possibility of interfacing the MR scanner with an external optical motion-tracking system capable of determining the object's position with submillimeter accuracy and an update rate of 60 Hz is shown. Movement information on the object position (head) is used to compensate for motion in real time by updating the field of view (FOV) by recalculating the gradients and radiofrequency parameter of the MR scanner during acquisition of k-space data, based on tracking data. RESULTS: Results of rotation phantom, in vivo experiments, and implementation of three different MRI sequences, 2D spin echo, 3D gradient echo, and echo planar imaging, are presented. Finally, the proposed method is compared with the prospective motion correction software available on the scanner software. CONCLUSION: A prospective motion correction method that works in real time only by updating the FOV of the MR scanner is presented. Results show the feasibility of using an external optical motion-tracking system to compensate for strong and fast subject motion during acquisition.