Three-dimensional in vivo imaging by a handheld dual-axes confocal microscope

Miniaturized confocal Raman and Laser-induced breakdown spectroscopy imaging system based on micro-electro-mechanical mirror

Detection of the elemental and molecular structural distribution with high resolution and miniaturization of unknown minerals is a main bottleneck in deep space exploration and geology analysis. The aim is to enhance the accuracy of the chemical analysis of micro-samples by combining the distribution information from Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS). The existing Raman-LIBS imaging methods are difficult to balance the imaging performance and system volume. There is an urgent need to develop a Raman-LIBS imaging method with miniaturization, and high imaging performance. A miniaturized Raman-LIBS imaging instrument based on the micro-electro-mechanical (MEMS) mirror has been developed to overcome these challenges. The instrument utilizes dual 2D MEMS mirror scanning technology to shorten the optical length of the system and improve the detection efficiency of hybrid spectral signals. The optical probe measures 94 mm × 66 mm, and has an axial focusing ability of approximately 40 nm, with a lateral resolution of approximately 700 nm for Raman maps and 9.5 μm for LIBS maps. As a proof experiment, 3D high-resolution Raman-LIBS hybrid spectral distribution maps of meteorite Tisserlitine 001 were obtained. The attainment of high imaging performance and miniaturization in hybrid spectral imaging is crucial for on-site chemical analysis. The proposed instrument enables in-situ spectrum and multispectral imaging with miniaturization, high spatial resolution, and high stability. The instrument is a powerful tool for composition and structural information characterization in the fields of space exploration and geological exploration.

Nanomaterial-based contrast agents

Medical imaging, which empowers the detection of physiological and pathological processes within living subjects, has a vital role in both preclinical and clinical diagnostics. Contrast agents are often needed to accompany anatomical data with functional information or to provide phenotyping of the disease in question. Many newly emerging contrast agents are based on nanomaterials as their high payloads, unique physicochemical properties, improved sensitivity and multimodality capacity are highly desired for many advanced forms of bioimaging techniques and applications. Here, we review the developments in the field of nanomaterial-based contrast agents. We outline important nanomaterial design considerations and discuss the effect on their physicochemical attributes, contrast properties and biological behaviour. We also describe commonly used approaches for formulating, functionalizing and characterizing these nanomaterials. Key applications are highlighted by categorizing nanomaterials on the basis of their X-ray, magnetic, nuclear, optical and/or photoacoustic contrast properties. Finally, we offer our perspectives on current challenges and emerging research topics as well as expectations for future advancements in the field.

Tunable Wide-Field Illumination and Single-Molecule Photoswitching with a Single MEMS Mirror

Homogeneous illumination in single-molecule localization microscopy (SMLM) is key for the quantitative analysis of super-resolution images. Therefore, different approaches for flat-field illumination have been introduced as alternative to the conventional Gaussian illumination. Here, we introduce a single microelectromechanical systems (MEMS) mirror as a tunable and cost-effective device for adapting wide-field illumination in SMLM. In flat-field mode the MEMS allowed for consistent SMLM metrics across the entire field of view. Employing single-molecule photoswitching, we developed a simple yet powerful routine to benchmark different illumination schemes on the basis of local emitter brightness and ON-state lifetime. Moreover, we propose that tuning the MEMS beyond optimal flat-field conditions enables to study the kinetics of photoswitchable fluorophores within a single acquisition.

A colorful approach towards developing new nano-based imaging contrast agents for improved cancer detection

Providing physicians with new imaging agents to help detect cancer with better sensitivity and specificity has the potential to significantly improve patient outcomes. Development of new imaging agents could offer improved early cancer detection during routine screening or help surgeons identify tumor margins for surgical resection. In this study, we evaluate the optical properties of a colorful class of dyes and pigments that humans routinely encounter. The pigments are often used in tattoo inks and the dyes are FDA approved for the coloring of foods, drugs, and cosmetics. We characterized their absorption, fluorescence and Raman scattering properties in the hopes of identifying a new panel of dyes that offer exceptional imaging contrast. We found that some of these coloring agents, coined as "optical inks", exhibit a multitude of useful optical properties, outperforming some of the clinically approved imaging dyes on the market. The best performing optical inks (Green 8 and Orange 16) were further incorporated into liposomal nanoparticles to assess their tumor targeting and optical imaging potential. Mouse xenograft models of colorectal, cervical and lymphoma tumors were used to evaluate the newly developed nano-based imaging contrast agents. After intravenous injection, fluorescence imaging revealed significant localization of the new "optical ink" liposomal nanoparticles in all three tumor models as opposed to their neighboring healthy tissues (p < 0.05). If further developed, these coloring agents could play important roles in the clinical setting. A more sensitive imaging contrast agent could enable earlier cancer detection or help guide surgical resection of tumors, both of which have been shown to significantly improve patient survival.

The potential of fluorescent dyes-comparative study of Nile red and three derivatives for the detection of microplastics

During the last years, microplastics in the environment came to the fore in environmental science research. For an appropriate risk assessment, it is essential to know the levels of microplastic contamination in the environment. In the field of microplastic detection, extensive research has been carried out in recent years. While common methods such as Raman spectroscopy and pyrolysis GC-MS are time-consuming and require trained staff and expensive equipment, there is the need for a cheap and easily applicable method. Staining microplastics with the fluorescent dye Nile red (NR) has a high potential to fulfill these criteria. In our work, we tested Nile red and newly developed derivatives, with the aim of achieving greater selectivity for plastic particles and more intense fluorescence. In addition, the influence of using different solvents and water at different pH values in the dyeing process was investigated by analyzing solid sample fluorescence spectra of dyed microplastics and natural particles. Finally, the method developed from the acquired knowledge was tested for sea salt. Graphical abstract.

Image computing for fibre-bundle endomicroscopy: A review

Endomicroscopy is an emerging imaging modality, that facilitates the acquisition of in vivo, in situ optical biopsies, assisting diagnostic and potentially therapeutic interventions. While there is a diverse and constantly expanding range of commercial and experimental optical biopsy platforms available, fibre-bundle endomicroscopy is currently the most widely used platform and is approved for clinical use in a range of clinical indications. Miniaturised, flexible fibre-bundles, guided through the working channel of endoscopes, needles and catheters, enable high-resolution imaging across a variety of organ systems. Yet, the nature of image acquisition though a fibre-bundle gives rise to several inherent characteristics and limitations necessitating novel and effective image pre- and post-processing algorithms, ranging from image formation, enhancement and mosaicing to pathology detection and quantification. This paper introduces the underlying technology and most prevalent clinical applications of fibre-bundle endomicroscopy, and provides a comprehensive, up-to-date, review of relevant image reconstruction, analysis and understanding/inference methodologies. Furthermore, current limitations as well as future challenges and opportunities in fibre-bundle endomicroscopy computing are identified and discussed.

Software-Based Phase Control, Video-Rate Imaging, and Real-Time Mosaicing With a Lissajous-Scanned Confocal Microscope

We present software-based methods for automatic phase control and for mosaicing high-speed, Lissajous-scanned images. To achieve imaging speeds fast enough for mosaicing, we first increase the image update rate tenfold from 3 to 30 Hz, then vertically interpolate each sparse image in real-time to eliminate fixed pattern noise. We validate our methods by imaging fluorescent beads and automatically maintaining phase control over the course of one hour. We then image fixed mouse brain tissues at varying update rates and compare the resulting mosaics. Using reconstructed image data as feedback for phase control eliminates the need for phase sensors and feedback controllers, enabling long-term imaging experiments without additional hardware. Mosaicing subsampled images results in video-rate imaging speeds, nearly fully recovered spatial resolution, and millimeter-scale fields of view.

Low-power optical beam steering by microelectromechanical waveguide gratings

Optical beam steering is key for optical communications, laser mapping (lidar), and medical imaging. For these applications, integrated photonics is an enabling technology that can provide miniaturized, lighter, lower-cost, and more power-efficient systems. However, common integrated photonic devices are too power demanding. Here, we experimentally demonstrate, for the first time, to the best of our knowledge, beam steering by microelectromechanical (MEMS) actuation of a suspended silicon photonic waveguide grating. Our device shows up to 5.6° beam steering with 20 V actuation and power consumption below the μW level, i.e., more than five orders of magnitude lower power consumption than previous thermo-optic tuning methods. The novel combination of MEMS with integrated photonics presented in this work lays ground for the next generation of power-efficient optical beam steering systems.

MEMS-in-the-lens architecture for a miniature high-NA laser scanning microscope

Laser scanning microscopes can be miniaturized for in vivo imaging by substituting optical microelectromechanical system (MEMS) devices in place of larger components. The emergence of multifunctional active optical devices can support further miniaturization beyond direct component replacement because those active devices enable diffraction-limited performance using simpler optical system designs. In this paper, we propose a catadioptric microscope objective lens that features an integrated MEMS device for performing biaxial scanning, axial focus adjustment, and control of spherical aberration. The MEMS-in-the-lens architecture incorporates a reflective MEMS scanner between a low-numerical-aperture back lens group and an aplanatic hyperhemisphere front refractive element to support high-numerical-aperture imaging. We implemented this new optical system using a recently developed hybrid polymer/silicon MEMS three-dimensional scan mirror that features an annular aperture that allows it to be coaxially aligned within the objective lens without the need for a beam splitter. The optical performance of the active catadioptric system is simulated and imaging of hard targets and human cheek cells is demonstrated with a confocal microscope that is based on the new objective lens design.

MEMS 3D Scan Mirror with SU-8 Membrane and Flexures for High NA Microscopy

We demonstrate a MEMS beam scanner capable of biaxial scanning with simultaneous focus control, for integration into a handheld confocal microscope for skin imaging. The device is based on a dual axis gimbal structure with an integrated largestroke deformable mirror. SU-8 polymer is used to construct both the deformable membrane as well as the torsional hinges for biaxial scanning. The 4 mm diameter mirror can perform raster pattern scanning with a range of +/- 1.5 degrees and Lissajous scanning with a range of +/- 3 degrees (mechanical scan angle), and has a maximum deflection of 9 um for focus control. The design, fabrication and characterization of the opto-mechanical performance of the MEMS device are presented in this paper.

Three-dimensional super-resolution correlation-differential confocal microscopy with nanometer axial focusing accuracy

We present a correlation-differential confocal microscopy (CDCM), a novel method that can simultaneously improve the three-dimensional spatial resolution and axial focusing accuracy of confocal microscopy (CM). CDCM divides the CM imaging light path into two paths, where the detectors are before and after the focus with an equal axial offset in opposite directions. Then, the light intensity signals received from the two paths are processed by the correlation product and differential subtraction to improve the CM spatial resolution and axial focusing accuracy, respectively. Theoretical analyses and preliminary experiments indicate that, for the excitation wavelength of λ = 405 nm, numerical aperture of NA = 0.95, and the normalized axial offset of uM = 5.21, the CDCM resolution is improved by more than 20% and more than 30% in the lateral and axial directions, respectively, compared with that of the CM. Also, the axial focusing resolution important for the imaging of sample surface profiles is improved to 1 nm.

Three-dimensional resolution-enhancement divided aperture correlation-differential confocal microscopy with nanometer axial focusing capability

Divided aperture confocal microscopy (DACM) provides an improved imaging depth, imaging contrast, and working distance at the expense of spatial resolution. Here, we present a new method-divided aperture correlation-differential confocal microscopy (DACDCM) to improve the DACM resolution and the focusing capability, without changing the DACM configuration. DACDCM divides the DACM image spot into two round regions symmetrical about the optical axis. Then the light intensity signals received simultaneously from two round regions by a charge-coupled device (CCD) are processed by correlation manipulation and differential subtraction to improve the DACM spatial resolution and axial focusing capability, respectively. Theoretical analysis and preliminary experiments indicate that, for the excitation wavelength of λ = 632.8 nm, numerical aperture NA = 0.8, and normalized offset v_M = 3.2 of the two regions, the DACDCM resolution is improved by 32.5% and 43.1% in the x and z directions, simultaneously, compared with that of the DACM. The axial focusing resolution used for the sample surface profile imaging was also significantly improved to 2 nm.

New Endoscopic Imaging Technology Based on MEMS Sensors and Actuators

Over the last decade, optical fiber-based forms of microscopy and endoscopy have extended the realm of applicability for many imaging modalities. Optical fiber-based imaging modalities permit the use of remote illumination sources and enable flexible forms supporting the creation of portable and hand-held imaging instrumentations to interrogate within hollow tissue cavities. A common challenge in the development of such devices is the design and integration of miniaturized optical and mechanical components. Until recently, microelectromechanical systems (MEMS) sensors and actuators have been playing a key role in shaping the miniaturization of these components. This is due to the precision mechanics of MEMS, microfabrication techniques, and optical functionality enabling a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. Many promising results from MEMS based optical fiber endoscopy have demonstrated great potentials for clinical translation. In this article, reviews of MEMS sensors and actuators for various fiber-optical endoscopy such as fluorescence, optical coherence tomography, confocal, photo-acoustic, and two-photon imaging modalities will be discussed. This advanced MEMS based optical fiber endoscopy can provide cellular and molecular features with deep tissue penetration enabling guided resections and early cancer assessment to better treatment outcomes.

Pilot Clinical Evaluation of a Confocal Microlaparoscope for Ovarian Cancer Detection

OBJECTIVE

The aim of this study is to evaluate the performance of a confocal fluorescence microlaparoscope for in vivo detection of ovarian cancer.

METHODS/MATERIALS

Seventy-one patients scheduled for open or laparoscopic oophorectomy were consented for the imaging study. High-resolution confocal microlaparoscopic images of the epithelial surface of the ovary were acquired in vivo or ex vivo after tissue staining using acridine orange. Standard histologic evaluation of extracted tissue samples was performed and used as the gold standard of disease diagnosis. Trained human observers from different specialties viewed the microlaparoscopic images, rating each image on a 6-point scale ranging from "definitely not cancer" to "definitely cancer." Receiver operating characteristic curves were generated using these scores and the gold standard histopathologic diagnosis. Area under the receiver operating characteristic curve (AUC) was calculated as a performance metric.

RESULTS

Forty-five of the consented patients were used in the final evaluation study. From these 45 patients, 63 tissue locations or samples were identified and imaged with the confocal microlaparoscope. Twenty of the samples were high-grade cancers, and the remaining 43 samples were normal or noncancerous. Twenty-three of the samples were imaged in vivo, and the remaining 40 samples were imaged ex vivo. The average AUC score and standard error (SE) for detection of cancer in all images were 0.88 and 0.02, respectively. An independent-samples t test was conducted to compare AUC scores for in vivo and ex vivo conditions. No statistically significant difference in the AUC score for in vivo (AUC, 0.850; SE, 0.049) and ex vivo (AUC, 0.888; SE, 0.027) conditions was observed, t(6) = 1.318, P = 0.2355.

CONCLUSIONS

Area under the receiver operating characteristic curve scores indicate that high-resolution in vivo images obtained by the confocal laparoscope can distinguish between normal and malignant ovarian surface epithelium. In addition, in vivo performance is similar to that which can be obtained from ex vivo tissue.

Imaging Functional Nucleic Acid Delivery to Skin

Monogenic skin diseases arise from well-defined single gene mutations, and in some cases a single point mutation. As the target cells are superficial, these diseases are ideally suited for treatment by nucleic acid-based therapies as well as monitoring through a variety of noninvasive imaging technologies. Despite the accessibility of the skin, there remain formidable barriers for functional delivery of nucleic acids to the target cells within the dermis and epidermis. These barriers include the stratum corneum and the layered structure of the skin, as well as more locally, the cellular, endosomal and nuclear membranes. A wide range of technologies for traversing these barriers has been described and moderate success has been reported for several approaches. The lessons learned from these studies include the need for combinations of approaches to facilitate nucleic acid delivery across these skin barriers and then functional delivery across the cellular and nuclear membranes for expression (e.g., reporter genes, DNA oligonucleotides or shRNA) or into the cytoplasm for regulation (e.g., siRNA, miRNA, antisense oligos). The tools for topical delivery that have been evaluated include chemical, physical and electrical methods, and the development and testing of each of these approaches has been greatly enabled by imaging tools. These techniques allow delivery and real time monitoring of reporter genes, therapeutic nucleic acids and also triplex nucleic acids for gene editing. Optical imaging is comprised of a number of modalities based on properties of light-tissue interaction (e.g., scattering, autofluorescence, and reflectance), the interaction of light with specific molecules (e.g., absorbtion, fluorescence), or enzymatic reactions that produce light (bioluminescence). Optical imaging technologies operate over a range of scales from macroscopic to microscopic and if necessary, nanoscopic, and thus can be used to assess nucleic acid delivery to organs, regions, cells and even subcellular structures. Here we describe the animal models, reporter genes, imaging approaches and general strategies for delivery of nucleic acids to cells in the skin for local expression (e.g., plasmid DNA) or gene silencing (e.g., siRNA) with the intent of developing nucleic acid-based therapies to treat diseases of the skin.

Micro-optical design of a three-dimensional microlens scanner for vertically integrated micro-opto-electro-mechanical systems

This paper presents the optical design of a miniature 3D scanning system, which is fully compatible with the vertical integration technology of micro-opto-electro-mechanical systems (MOEMS). The constraints related to this integration strategy are considered, resulting in a simple three-element micro-optical setup based on an afocal scanning microlens doublet and a focusing microlens, which is tolerant to axial position inaccuracy. The 3D scanning is achieved by axial and lateral displacement of microlenses of the scanning doublet, realized by micro-electro-mechanical systems microactuators (the transmission scanning approach). Optical scanning performance of the system is determined analytically by use of the extended ray transfer matrix method, leading to two different optical configurations, relying either on a ball lens or plano-convex microlenses. The presented system is aimed to be a core component of miniature MOEMS-based optical devices, which require a 3D optical scanning function, e.g., miniature imaging systems (confocal or optical coherence microscopes) or optical tweezers.

Trends in fluorescence image-guided surgery for gliomas

Mounting evidence suggests that a more extensive surgical resection is associated with an improved life expectancy for both low-grade and high-grade glioma patients. However, radiographically complete resections are not often achieved in many cases because of the lack of sensitivity and specificity of current neurosurgical guidance techniques at the margins of diffuse infiltrative gliomas. Intraoperative fluorescence imaging offers the potential to improve the extent of resection and to investigate the possible benefits of resecting beyond the radiographic margins. Here, we provide a review of wide-field and high-resolution fluorescence-imaging strategies that are being developed for neurosurgical guidance, with a focus on emerging imaging technologies and clinically viable contrast agents. The strengths and weaknesses of these approaches will be discussed, as well as issues that are being addressed to translate these technologies into the standard of care.

Miniaturized fiber-coupled confocal fluorescence microscope with an electrowetting variable focus lens using no moving parts

We report a miniature, lightweight fiber-coupled confocal fluorescence microscope that incorporates an electrowetting variable focus lens to provide axial scanning for full three-dimensional (3D) imaging. Lateral scanning is accomplished by coupling our device to a laser-scanning confocal microscope through a coherent imaging fiber-bundle. The optical components of the device are combined in a custom 3D-printed adapter with an assembled weight of <2  g that can be mounted onto the head of a mouse. Confocal sectioning provides an axial resolution of ∼12  μm and an axial scan range of ∼80  μm. The lateral field-of-view is 300 μm, and the lateral resolution is 1.8 μm. We determined these parameters by imaging fixed sections of mouse neuronal tissue labeled with green fluorescent protein (GFP) and fluorescent bead samples in agarose gel. To demonstrate viability for imaging intact tissue, we resolved multiple optical sections of ex vivo mouse olfactory nerve fibers expressing yellow fluorescent protein (YFP).

Atherosclerotic plaque targeting mechanism of long-circulating nanoparticles established by multimodal imaging

Atherosclerosis is a major cause of global morbidity and mortality that could benefit from novel targeted therapeutics. Recent studies have shown efficient and local drug delivery with nanoparticles, although the nanoparticle targeting mechanism for atherosclerosis has not yet been fully elucidated. Here we used in vivo and ex vivo multimodal imaging to examine permeability of the vessel wall and atherosclerotic plaque accumulation of fluorescently labeled liposomal nanoparticles in a rabbit model. We found a strong correlation between permeability as established by in vivo dynamic contrast enhanced magnetic resonance imaging and nanoparticle plaque accumulation with subsequent nanoparticle distribution throughout the vessel wall. These key observations will enable the development of nanotherapeutic strategies for atherosclerosis.

Advances in imaging probes and optical microendoscopic imaging techniques for early in vivo cancer assessment

A new chapter in the history of medical diagnosis happened when the first X-ray technology was invented in the late 1800s. Since then, many non-invasive and minimally invasive imaging techniques have been invented for clinical diagnosis to research in cellular biology, drug discovery, and disease monitoring. These imaging modalities have leveraged the benefits of significant advances in computer, electronics, and information technology and, more recently, targeted molecular imaging. The development of targeted contrast agents such as fluorescent and nanoparticle probes coupled with optical imaging techniques has made it possible to selectively view specific biological events and processes in both in vivo and ex vivo systems with great sensitivity and selectivity. Thus, the combination of targeted molecular imaging probes and optical imaging techniques have become a mainstay in modern medicinal and biological research. Many promising results have demonstrated great potentials to translate to clinical applications. In this review, we describe a discussion of employing imaging probes and optical microendoscopic imaging techniques for cancer diagnosis.

Smart-phone based computational microscopy using multi-frame contact imaging on a fiber-optic array

We demonstrate a cellphone based contact microscopy platform, termed Contact Scope, which can image highly dense or connected samples in transmission mode. Weighing approximately 76 grams, this portable and compact microscope is installed on the existing camera unit of a cellphone using an opto-mechanical add-on, where planar samples of interest are placed in contact with the top facet of a tapered fiber-optic array. This glass-based tapered fiber array has ~9 fold higher density of fiber optic cables on its top facet compared to the bottom one and is illuminated by an incoherent light source, e.g., a simple light-emitting-diode (LED). The transmitted light pattern through the object is then sampled by this array of fiber optic cables, delivering a transmission image of the sample onto the other side of the taper, with ~3× magnification in each direction. This magnified image of the object, located at the bottom facet of the fiber array, is then projected onto the CMOS image sensor of the cellphone using two lenses. While keeping the sample and the cellphone camera at a fixed position, the fiber-optic array is then manually rotated with discrete angular increments of e.g., 1-2 degrees. At each angular position of the fiber-optic array, contact images are captured using the cellphone camera, creating a sequence of transmission images for the same sample. These multi-frame images are digitally fused together based on a shift-and-add algorithm through a custom-developed Android application running on the smart-phone, providing the final microscopic image of the sample, visualized through the screen of the phone. This final computation step improves the resolution and also removes spatial artefacts that arise due to non-uniform sampling of the transmission intensity at the fiber optic array surface. We validated the performance of this cellphone based Contact Scope by imaging resolution test charts and blood smears.

A handheld electromagnetically actuated fiber optic raster scanner for reflectance confocal imaging of biological tissues

We present a hand-held device aimed for reflectance-mode confocal imaging of biological tissues. The device consists of a light carrying optical fiber and a miniaturized raster scanner located at the distal end of the fiber. It is fabricated by mounting a polarization maintaining optical fiber on a cantilever beam that is attached to another beam such that their bending axes are perpendicular to each other. Fiber scanner is driven by electromagnetic forces and enables large fiber deflections with low driving currents. Optical resolutions of the system are 1.55 and 8.45 μm in the lateral and axial directions, respectively. Functionality of the system is demonstrated by obtaining confocal images of a fly wing and a human colon tissue sample.

Optical imaging techniques for point-of-care diagnostics

Improving access to effective and affordable healthcare has long been a global endeavor. In this quest, the development of cost-effective and easy-to-use medical testing equipment that enables rapid and accurate diagnosis is essential to reduce the time and costs associated with healthcare services. To this end, point-of-care (POC) diagnostics plays a crucial role in healthcare delivery in both developed and developing countries by bringing medical testing to patients, or to sites near patients. As the diagnosis of a wide range of diseases, including various types of cancers and many endemics, relies on optical techniques, numerous compact and cost-effective optical imaging platforms have been developed in recent years for use at the POC. Here, we review the state-of-the-art optical imaging techniques that can have a significant impact on global health by facilitating effective and affordable POC diagnostics.

Optimized off-axis cylindrical mirror-focused line-scanning system for optical coherence tomography imaging applications

The parameters of an off-axis cylindrical mirror-focused line-scanning system were studied to optimize the flatness of the 2 mm scan field. The scanning system parameters included the beam size, the distance between the scanning and the focusing mirror, the angle between the incident beam and the reflected beam, the optical scan angle, and the effective focal length of the cylindrical mirror. Because of the off-axis line-scanning system configuration, the scanning could be carried out either in the tangential (Y-scan) or in the sagittal (X-scan) plane. A 53 nm spectral bandwidth light source was used to evaluate the imaging performance of the scanning system. Since reflective optics is employed in this work for focusing, the scanning system could be used with a higher spectral bandwidth light source for optical coherence tomography applications. The effect of the angle between of the incident and reflected beams, the distance between the mirrors, the focal length of the cylindrical mirror and the scanning directions, on the flatness of the scan field were studied. It was proved that the sagittal scanning is least sensitive to variations in scanning system parameters and thus provides maximum flexibility in design.

In vivo near-infrared dual-axis confocal microendoscopy in the human lower gastrointestinal tract

Near-infrared confocal microendoscopy is a promising technique for deep in vivo imaging of tissues and can generate high-resolution cross-sectional images at the micron-scale. We demonstrate the use of a dual-axis confocal (DAC) near-infrared fluorescence microendoscope with a 5.5-mm outer diameter for obtaining clinical images of human colorectal mucosa. High-speed two-dimensional en face scanning was achieved through a microelectromechanical systems (MEMS) scanner while a micromotor was used for adjusting the axial focus. In vivo images of human patients are collected at 5 frames/sec with a field of view of 362×212 μm(2) and a maximum imaging depth of 140 μm. During routine endoscopy, indocyanine green (ICG) was topically applied a nonspecific optical contrasting agent to regions of the human colon. The DAC microendoscope was then used to obtain microanatomic images of the mucosa by detecting near-infrared fluorescence from ICG. These results suggest that DAC microendoscopy may have utility for visualizing the anatomical and, perhaps, functional changes associated with colorectal pathology for the early detection of colorectal cancer.

Vertical optical sectioning using a magnetically driven confocal microscanner aimed for in vivo clinical imaging

This paper presents a confocal microscanner for direct vertical optical sectioning of biological samples. Confocal imaging is performed by transverse (X-axis) and axial (Z-axis) scanning of a focused laser beam using an optical fiber and a microlens respectively. The actuators are fabricated by laser micromachining techniques and are driven by electromagnetic forces. Optical and mechanical performance of the system is predicted by simulation software packages and characterized by experimental measurements. The scanner has lateral resolution of 3.87 µm and axial resolution of 10.68 µm with a field of view of 145 µm in X and 190 µm in Z directions. Confocal imaging of a polymer layer deposited on a silicon wafer and onion epidermal cells is demonstrated.

A 2D MEMS mirror with sidewall electrodes applied for confocal MACROscope imaging

This paper presents microelectromechanical system micromirrors with sidewall electrodes applied for use as a Confocal MACROscope for biomedical imaging. The MACROscope is a fluorescence and brightfield confocal laser scanning microscope with a very large field of view. In this paper, a microelectromechanical system mirror with sidewall electrodes replaces the galvo-scanner and XYZ-stage to improve the confocal MACROscope design and obtain an image. Two micromirror-based optical configurations are developed and tested to optimize the optical design through scanning angle, field of view and numerical aperture improvement. Meanwhile, the scanning frequency and control waveform of the micromirror are tested. Analysing the scan frequency and waveform becomes a key factor to optimize the micromirror-based confocal MACROscope. When the micromirror is integrated into the MACROscope and works at 40 Hz, the micromirror with open-loop control possesses good repeatability, so that the synchronization among the scanner, XYZ-stage and image acquisition can be realized. A laser scanning microscope system based on the micromirror with 2 μm width torsion bars was built and a 2D image was obtained as well. This work forms the experimental basis for building a practical confocal MACROscope.

Confocal endomicroscopy: instrumentation and medical applications

Advances in fiber optic technology and miniaturized optics and mechanics have propelled confocal endomicroscopy into the clinical realm. This high resolution, non-invasive imaging technology provides the ability to microscopically evaluate cellular and sub-cellular features in tissue in vivo by optical sectioning. Because many cancers originate in epithelial tissues accessible by endoscopes, confocal endomicroscopy has been explored to detect regions of possible neoplasia at an earlier stage by imaging morphological features in vivo that are significant in histopathologic evaluation. This technique allows real-time assessment of tissue which may improve diagnostic yield by guiding biopsy. Research and development continues to reduce the overall size of the imaging probe, increase the image acquisition speed, and improve resolution and field of view of confocal endomicroscopes. Technical advances will continue to enable application to less accessible organs and more complex systems in the body. Lateral and axial resolutions down to 0.5 and 3 μm, respectively, field of view as large as 800 × 450 μm, and objective lens and total probe outer diameters down to 0.35 and 1.25 mm, respectively, have been achieved. We provide a review of the historical developments of confocal imaging in vivo, the evolution of endomicroscope instrumentation, and the medical applications of confocal endomicroscopy.

Future and advances in endoscopy

The future of endoscopy will be dictated by rapid technological advances in the development of light sources, optical fibers, and miniature scanners that will allow for images to be collected in multiple spectral regimes, with greater tissue penetration, and in three dimensions. These engineering breakthroughs will be integrated with novel molecular probes that are highly specific for unique proteins to target diseased tissues. Applications include early cancer detection by imaging molecular changes that occur before gross morphological abnormalities, personalized medicine by visualizing molecular targets specific to individual patients, and image guided therapy by localizing tumor margins and monitoring for recurrence.

Future and advances in endoscopy

The future of endoscopy will be dictated by rapid technological advances in the development of light sources, optical fibers, and miniature scanners that will allow for images to be collected in multiple spectral regimes, with greater tissue penetration, and in three dimensions. These engineering breakthroughs will be integrated with novel molecular probes that are highly specific for unique proteins to target diseased tissues. Applications include early cancer detection by imaging molecular changes that occur before gross morphological abnormalities, personalized medicine by visualizing molecular targets specific to individual patients, and image guided therapy by localizing tumor margins and monitoring for recurrence.

In vivo imaging of human and mouse skin with a handheld dual-axis confocal fluorescence microscope

Advancing molecular therapies for the treatment of skin diseases will require the development of new tools that can reveal spatiotemporal changes in the microanatomy of the skin and associate these changes with the presence of the therapeutic agent. For this purpose, we evaluated a handheld dual-axis confocal (DAC) microscope that is capable of in vivo fluorescence imaging of skin, using both mouse models and human skin. Individual keratinocytes in the epidermis were observed in three-dimensional image stacks after topical administration of near-infrared (NIR) dyes as contrast agents. This suggested that the DAC microscope may have utility in assessing the clinical effects of a small interfering RNA (siRNA)-based therapeutic (TD101) that targets the causative mutation in pachyonychia congenita (PC) patients. The data indicated that (1) formulated indocyanine green (ICG) readily penetrated hyperkeratotic PC skin and normal callused regions compared with nonaffected areas, and (2) TD101-treated PC skin revealed changes in tissue morphology, consistent with reversion to nonaffected skin compared with vehicle-treated skin. In addition, siRNA was conjugated to NIR dye and shown to penetrate through the stratum corneum barrier when topically applied to mouse skin. These results suggest that in vivo confocal microscopy may provide an informative clinical end point to evaluate the efficacy of experimental molecular therapeutics.

Miniaturization of free space optical systems

Coherent illumination enables not only integrated optics, but also miniaturized free-space optics that takes advantage of the amplitude and phase control afforded by optical microelectromechanical systems (MEMS) and photonic crystals. These technologies also provide a practical and cost-effective means for integration and packaging of optical systems. The properties of miniaturized optical systems based on optical MEMS and photonic crystals are described, and efficient analysis and design approaches to miniaturized optical scanners and tunable diffractive optical elements are demonstrated. The impact of photonic crystals on free-space micro-optics is discussed.

MEMS-Based Dual Axes Confocal Microendoscopy

We demonstrate a miniature, near-infrared microscope (λ = 785 nm) that uses a novel dual axes confocal architecture. Scalability is achieved with post-objective scanning, and a MEMS mirror provides real time (>4 Hz) in vivo imaging. This instrument can achieve sub-cellular resolution with deep tissue penetration and large field of view. An endoscope-compatible version can image digestive tract epithelium to guide tissue biopsy and monitor therapy.

Handheld histology-equivalent sectioning laser-scanning confocal optical microscope for interventional imaging

A handheld, forward-imaging, laser-scanning confocal microscope (LSCM) demonstrating optical sectioning comparable with microtome slice thicknesses in conventional histology, targeted towards interventional imaging, is reported. Fast raster scanning (approximately 2.5 kHz line scan rate, 3.0-5.0 frames per second) was provided by a 2-axis microelectromechanical system (MEMS) scanning mirror fabricated by a method compatible with complementary metal-oxide-semiconductor (CMOS) processing. Cost-effective rapid-prototyped packaging combined the MEMS mirror with micro-optical components into a probe with 18 mm outer diameter and 54 mm rigid length. ZEMAX optical design simulations indicate the ability of the handheld optical system to obtain lateral resolution of 0.31 and axial resolution of 2.85 microm. Lateral and axial resolutions are experimentally measured at 0.5 microm and 4.2 microm respectively, with field of view of 200 x 125 microm. Results of reflectance imaging of ex vivo swine liver, and fluorescence imaging of the expression of cytokeratin and mammaglobin tumor biomarkers in epithelial human breast tissue from metastatic breast cancer patients are presented. The results indicate that inexpensive, portable handheld optical microscopy tools based on silicon micromirror technologies could be important in interventional imaging, complementing existing coarse-resolution techniques to improve the efficacy of disease diagnosis, image-guided excisional microsurgery, and monitored photodynamic therapy.

Increased interstitial pressure improves nucleic acid delivery to skin enabling a comparative analysis of constitutive promoters

Nucleic acid-based therapies hold great promise for treatment of skin disorders if delivery challenges can be overcome. To investigate one mechanism of nucleic acid delivery to keratinocytes, a fixed mass of expression plasmid was intradermally injected into mouse footpads in different volumes, and reporter expression was monitored by intravital imaging or skin sectioning. Reporter gene expression increased with higher delivery volumes, suggesting that pressure drives nucleic acid uptake into cells after intradermal injections similar to previously published studies for muscle and liver. For spatiotemporal analysis of reporter gene expression, a dual-axis confocal (DAC) fluorescence microscope was used for intravital imaging following intradermal injections. Individual keratinocytes expressing hMGFP were readily visualized in vivo and initially appeared to preferentially express in the stratum granulosum and subsequently migrate to the stratum corneum over time. Fluorescence microscopy of frozen skin sections confirmed the patterns observed by intravital imaging. Intravital imaging with the DAC microscope is a noninvasive method for probing spatiotemporal control of gene expression and should facilitate development and testing of new nucleic acid delivery technologies.

Assessing delivery and quantifying efficacy of small interfering ribonucleic acid therapeutics in the skin using a dual-axis confocal microscope

Transgenic reporter mice and advances in imaging instrumentation are enabling real-time visualization of cellular mechanisms in living subjects and accelerating the development of novel therapies. Innovative confocal microscope designs are improving their utility for microscopic imaging of fluorescent reporters in living animals. We develop dual-axis confocal (DAC) microscopes for such in vivo studies and create mouse models where fluorescent proteins are expressed in the skin for the purpose of advancing skin therapeutics and transdermal delivery tools. Three-dimensional image volumes, through the different skin compartments of the epidermis and dermis, can be acquired in several seconds with the DAC microscope in living mice, and are comparable to histologic analyses of reporter protein expression patterns in skin sections. Intravital imaging with the DAC microscope further enables visualization of green fluorescent protein (GFP) reporter gene expression in the skin over time, and quantification of transdermal delivery of small interfering RNA (siRNA) and therapeutic efficacy. Visualization of transdermal delivery of nucleic acids will play an important role in the development of innovative strategies for treating skin pathologies.

Micromirror-scanned dual-axis confocal microscope utilizing a gradient-index relay lens for image guidance during brain surgery

A fluorescence confocal microscope incorporating a 1.8-mm-diam gradient-index relay lens is developed for in vivo histological guidance during resection of brain tumors. The microscope utilizes a dual-axis confocal architecture to efficiently reject out-of-focus light for high-contrast optical sectioning. A biaxial microelectromechanical system (MEMS) scanning mirror is actuated at resonance along each axis to achieve a large field of view with low-voltage waveforms. The unstable Lissajous scan, which results from actuating the orthogonal axes of the MEMS mirror at highly disparate resonance frequencies, is optimized to fully sample 500x500 pixels at two frames per second. Optically sectioned fluorescence images of brain tissues are obtained in living mice to demonstrate the utility of this microscope for image-guided resections.

MEMS-based handheld confocal microscope for in-vivo skin imaging

This paper describes a handheld laser scanning confocal microscope for skin microscopy. Beam scanning is accomplished with an electromagnetic MEMS bi-axial micromirror developed for pico projector applications, providing 800 x 600 (SVGA) resolution at 56 frames per second. The design uses commercial objective lenses with an optional hemisphere front lens, operating with a range of numerical aperture from NA=0.35 to NA=1.1 and corresponding diagonal field of view ranging from 653 microm to 216 microm. Using NA=1.1 and a laser wavelength of 830 nm we measured the axial response to be 1.14 mum full width at half maximum, with a corresponding 10%-90% lateral edge response of 0.39 mum. Image examples showing both epidermal and dermal features including capillary blood flow are provided. These images represent the highest resolution and frame rate yet achieved for tissue imaging with a MEMS bi-axial scan mirror.

Invited review article: Imaging techniques for harmonic and multiphoton absorption fluorescence microscopy

We review the current state of multiphoton microscopy. In particular, the requirements and limitations associated with high-speed multiphoton imaging are considered. A description of the different scanning technologies such as line scan, multifoci approaches, multidepth microscopy, and novel detection techniques is given. The main nonlinear optical contrast mechanisms employed in microscopy are reviewed, namely, multiphoton excitation fluorescence, second harmonic generation, and third harmonic generation. Techniques for optimizing these nonlinear mechanisms through a careful measurement of the spatial and temporal characteristics of the focal volume are discussed, and a brief summary of photobleaching effects is provided. Finally, we consider three new applications of multiphoton microscopy: nonlinear imaging in microfluidics as applied to chemical analysis and the use of two-photon absorption and self-phase modulation as contrast mechanisms applied to imaging problems in the medical sciences.

siRNA silencing of keratinocyte-specific GFP expression in a transgenic mouse skin model

Small interfering RNAs (siRNAs) can be designed to specifically and potently target and silence a mutant allele, with little or no effect on the corresponding wild-type allele expression, presenting an opportunity for therapeutic intervention. Although several siRNAs have entered clinical trials, the development of siRNA therapeutics as a new drug class will require the development of improved delivery technologies. In this study, a reporter mouse model (transgenic click beetle luciferase/humanized monster green fluorescent protein) was developed to enable the study of siRNA delivery to skin; in this transgenic mouse, green fluorescent protein reporter gene expression is confined to the epidermis. Intradermal injection of siRNAs targeting the reporter gene resulted in marked reduction of green fluorescent protein expression in the localized treatment areas as measured by histology, real-time quantitative polymerase chain reaction and intravital imaging using a dual-axes confocal fluorescence microscope. These results indicate that this transgenic mouse skin model, coupled with in vivo imaging, will be useful for development of efficient and 'patient-friendly' siRNA delivery techniques and should facilitate the translation of siRNA-based therapeutics to the clinic for treatment of skin disorders.

Optical contrast agents and imaging systems for detection and diagnosis of cancer

Molecular imaging has rapidly emerged as a discipline with the potential to impact fundamental biomedical research and clinical practice. Within this field, optical imaging offers several unique capabilities, based on the ability of cells and tissues to effect quantifiable changes in the properties of visible and near-infrared light. Beyond endogenous optical properties, the development of molecularly targeted contrast agents enables disease-specific morphologic and biochemical processes to be labeled with unique optical signatures. Optical imaging systems can then provide real-time visualization of pathophysiology at spatial scales from the subcellular to whole organ levels. In this article, we review fundamental techniques and recent developments in optical molecular imaging, emphasizing laboratory and clinical systems that aim to visualize the microscopic and macroscopic hallmarks of cancer.