Methods for imaging the structure and function of living tissues and cells: 3. Confocal microscopy and micro-radiology

Optical Coherence Tomography Imaging of Normal, Chronologically Aged, Photoaged and Photodamaged Skin: A Systematic Review

BACKGROUND

Optical coherence tomography (OCT) is capable of providing a noninvasive real-time cross-sectional image of the skin through light-based interferometry, a method sometimes described as "light-based ultrasound." One key application of OCT in dermatology is the visualization of dermal collagen during chronological aging, photoaging, or photodamage. These skin conditions are typically managed by the practitioner's subjective assessment of severity and response to therapy.

OBJECTIVE

The purpose of this review is to present available evidence on the ability of OCT to image normal, chronologically aged, photoaged and photodamaged skin in human subjects.

METHODS AND MATERIALS

The authors have searched Medline, PubMed, EMBASE, Web of Science, Google Scholar, and Cochrane Library databases for published literature on the imaging of skin collagen by OCT using the following search terms: "optical coherence tomography," "OCT," "skin," "collagen," "photoaging," "wrinkles," and "photodamage."

RESULTS

The search resulted in 23 articles investigating OCT-based skin collagen imaging, which met their search criteria.

CONCLUSION

The authors anticipate tremendous growth in the field of OCT-based skin imaging that will parallel the development ultrasound technology has experienced over the past 30 years. They foresee that the use of OCT imaging to evaluate skin aging will not only help identify pathological changes earlier, but will also assist in the evaluation of the response to therapy longitudinally without biopsy.

Optical coherence tomography (OCT) of collagen in normal skin and skin fibrosis

Optical coherence tomography (OCT) is a non-invasive imaging modality that is transforming clinical diagnosis in dermatology and other medical fields. OCT provides a cross-sectional evaluation of the epidermis and dermis and allows in vivo imaging of skin collagen. Upregulated collagen content is a key feature of fibrotic skin diseases. These diseases are often managed by the practitioner's subjective assessment of disease severity and response to therapies. The purpose of this review is to provide an overview of the principles of OCT and present available evidence on the ability of OCT to image skin collagen in vivo for the diagnosis and management of diseases characterized by skin fibrosis. We review OCT studies that characterize the collagen content in normal skin and fibrotic skin diseases including systemic sclerosis and hypertrophic scars secondary to burn, trauma, and other injury. We also highlight several limitations of OCT and suggest enhancements to improve OCT imaging of skin fibrosis. We conclude that OCT imaging has the potential to serve as an objective, non-invasive measure of collagen's status and disease progression for use in both research trials and clinical practice. The future use of OCT imaging as a quantitative imaging biomarker of fibrosis will help identify fibrosis and facilitate clinical examination in monitoring response to treatment longitudinally without relying on serial biopsies. The use of OCT technology for quantification of fibrosis is in the formative stages and we foresee tremendous growth potential, similar to the ultrasound development paradigm that evolved over the past 30 years.

'Go with the flow ': a review of methods and advancements in blood flow imaging

Physics has delivered extraordinary developments in almost every facet of modern life. From the humble thermometer and stethoscope to X-Ray, CT, MRI, ultrasound, PET and radiotherapy, our health has been transformed by these advances yielding both morphological and functional metrics. Recently high resolution label-free imaging of the microcirculation at clinically relevant depths has become available in the research domain. In this paper, we present a comprehensive review on current imaging techniques, state-of-the-art advancements and applications, and general perspectives on the prospects for these modalities in the clinical realm.

Intraoperative confocal microscopy for brain tumors: a feasibility analysis in humans

BACKGROUND

The ability to diagnose brain tumors intraoperatively and identify tumor margins during resection could maximize resection and minimize morbidity. Advances in optical imaging enabled production of a handheld intraoperative confocal microscope.

OBJECTIVE

To present a feasibility analysis of the intraoperative confocal microscope for brain tumor resection.

METHODS

Thirty-three patients with brain tumor treated at Barrow Neurological Institute were examined. All patients received an intravenous bolus of sodium fluorescein before confocal imaging with the Optiscan FIVE 1 system probe. Optical biopsies were obtained within each tumor and along the tumor-brain interfaces. Corresponding pathologic specimens were then excised and processed. These data was compared by a neuropathologist to identify the concordance for tumor histology, grade, and margins.

RESULTS

Thirty-one of 33 lesions were tumors (93.9%) and 2 cases were identified as radiation necrosis (6.1%). Of the former, 25 (80.6%) were intra-axial and 6 (19.4%) were extra-axial. Intra-axial tumors were most commonly gliomas and metastases, while all extra-axial tumors were meningiomas. Among high-grade gliomas, vascular neoproliferation, as well as tumor margins, were identifiable using confocal imaging. Meningothelial and fibrous meningiomas were distinct on confocal microscopy--the latter featured spindle-shaped cells distinguishable from adjacent parenchyma. Other tumor histologies correlated well with standard neuropathology tissue preparations.

CONCLUSION

Intraoperative confocal microscopy is a practicable technology for the resection of human brain tumors. Preliminary analysis demonstrates reliability for a variety of lesions in identifying tumor cells and the tumor-brain interface. Further refinement of this technology depends upon the approval of tumor-specific fluorescent contrast agents for human use.

Subcellular Microanatomy by 3D Deconvolution Brightfield Microscopy: Method and Analysis Using Human Chromatin in the Interphase Nucleus

Anatomy has advanced using 3-dimensional (3D) studies at macroscopic (e.g., dissection, injection moulding of vessels, radiology) and microscopic (e.g., serial section reconstruction with light and electron microscopy) levels. This paper presents the first results in human cells of a new method of subcellular 3D brightfield microscopy. Unlike traditional 3D deconvolution and confocal techniques, this method is suitable for general application to brightfield microscopy. Unlike brightfield serial sectioning it has subcellular resolution. Results are presented of the 3D structure of chromatin in the interphase nucleus of two human cell types, hepatocyte and plasma cell. I show how the freedom to examine these structures in 3D allows greater morphological discrimination between and within cell types and the 3D structural basis for the classical “clock-face” motif of the plasma cell nucleus is revealed. Potential for further applications discussed.

Miniaturized handheld confocal microscopy for neurosurgery: results in an experimental glioblastoma model

INTRODUCTION

Recent developments in optical science and image processing have miniaturized the components required for confocal microscopy. Clinical confocal imaging applications have emerged, including assessment of colonic mucosal dysplasia during colonoscopy. We present our initial experience with handheld, miniaturized confocal imaging in a murine brain tumor model.

METHODS

Twelve C57/BL6 mice were implanted intracranially with 10(5) GL261 glioblastoma cells. The brains of 6 anesthetized mice each at 14 and 21 days after implantation were exposed surgically, and the brain surface was imaged using a handheld confocal probe affixed to a stereotactic frame. The probe was moved systematically over regions of normal and tumor-containing tissue. Intravenous fluorescein and topical acriflavine contrast agents were used. Biopsies were obtained at each imaging site beneath the probe and assessed histologically. Mice were killed after imaging.

RESULTS

Handheld confocal imaging produced exquisite images, well-correlated with corresponding histologic sections, of cellular shape and tissue architecture in murine brain infiltrated by glial neoplasm. Reproducible patterns of cortical vasculature, as well as normal gray and white matter, were identified. Imaging effectively distinguished between tumor and nontumor tissue, including infiltrative tumor margins. Margins were easily identified by observers without prior neuropathology training after minimum experience with the technology.

CONCLUSION

Miniaturized handheld confocal imaging may assist neurosurgeons in detecting infiltrative brain tumor margins during surgery. It may help to avoid sampling error during biopsy of heterogeneous glial neoplasms, with the potential to supplement conventional intraoperative frozen section pathology. Clinical trials are warranted on the basis of these promising initial results.

Mathematical modelling of tissue-engineered angiogenesis

We present a mathematical model for the vascularisation of a porous scaffold following implantation in vivo. The model is given as a set of coupled non-linear ordinary differential equations (ODEs) which describe the evolution in time of the amounts of the different tissue constituents inside the scaffold. Bifurcation analyses reveal how the extent of scaffold vascularisation changes as a function of the parameter values. For example, it is shown how the loss of seeded cells arising from slow infiltration of vascular tissue can be overcome using a prevascularisation strategy consisting of seeding the scaffold with vascular cells. Using certain assumptions it is shown how the system can be simplified to one which is partially tractable and for which some analysis is given. Limited comparison is also given of the model solutions with experimental data from the chick chorioallantoic membrane (CAM) assay.

Virtual histology

Confocal laser endomicroscopy enables in vivo microscopy of the mucosal layer of the GI-tract with subcellular resolution during ongoing endoscopy. Endomicroscopy opens a new door for immediate tissue and vessel analysis. Different types of diseases can be diagnosed with optical surface and subsurface analysis. Analysis of the in vivo microarchitecture can be used for targeting biopsies to relevant areas. Furthermore, subsurface imaging can unmask microscopic diseases - (microscopic colitis) or bacterial infection (Helicobacter pylori), for example. Molecular imaging is becoming feasible, and this will shortly open the door to new indications in gastrointestinal endoscopy. This chapter reviews the currently rapidly expanding clinical data about endomicroscopy and gives a look into future research.

Confocal laser endomicroscopy for gastrointestinal diseases

Confocal laser endomicroscopy enables in vivo microscopy of the mucosal layer of the gastrointestinal tract with subcellular resolution during ongoing endoscopy. Endomicroscopy opens the door to immediate tissue and vessel analysis. Different types of diseases can be diagnosed with optical surface and subsurface analysis. Analysis of the in vivo microarchitecture can be used for targeting biopsies to relevant areas, and subsurface imaging can unmask microscopic diseases or bacterial infection. Molecular imaging is becoming feasible, which will enable new indications in gastrointestinal endoscopy. This article reviews the current and rapidly expanding clinical data on endomicroscopy and gives a look into future research.

Fast fluorescence microscopy for imaging the dynamics of embryonic development

Live imaging has gained a pivotal role in developmental biology since it increasingly allows real-time observation of cell behavior in intact organisms. Microscopes that can capture the dynamics of ever-faster biological events, fluorescent markers optimal for in vivo imaging, and, finally, adapted reconstruction and analysis programs to complete data flow all contribute to this success. Focusing on temporal resolution, we discuss how fast imaging can be achieved with minimal prejudice to spatial resolution, photon count, or to reliably and automatically analyze images. In particular, we show how integrated approaches to imaging that combine bright fluorescent probes, fast microscopes, and custom post-processing techniques can address the kinetics of biological systems at multiple scales. Finally, we discuss remaining challenges and opportunities for further advances in this field.

In vivo confocal laser scanning microscopy and micropuncture in intact rat

BACKGROUND

Intravital microscopy theoretically provides the optimal conditions for studying specific organ functions. However, the application of microscopy in intact organs in vivo has been limited so far due to technical difficulties. The purpose of this study was to establish a method of in vivo confocal laser scanning microscopy (CLSM) for the study of endocytosis in proximal tubules of intact kidney.

METHODS

The left kidney of rats placed on a modified microscope stage was exposed and stabilized in a thermostatically controlled cup. The stage was then attached to an upright confocal microscope. Surface proximal tubules were microinfused with fluorescent albumin or transferrin. Single or time-series images of microinfused proximal tubules were recorded in reflection and/or fluorescence mode.

RESULTS

The stability of the kidney and the resolution of images were sufficient to visualize intracellular vesicles. Albumin and transferrin were initially observed at the brush border, then later internalized by proximal tubules and accumulated in lysosomes over a time period of 15 min. Furthermore, fusion of vesicles was observed in time-lapse images.

CONCLUSION

These results show that in vivo CLSM in intact kidney may be an excellent method to evaluate proximal tubular endocytosis and ligand trafficking.

A fluorescence confocal endomicroscope for in vivo microscopy of the upper- and the lower-GI tract

BACKGROUND

This report describes the development and the clinical evaluation of a novel confocal endomicroscope for obtaining fluorescence images of cellular morphology of the mucosae of the upper- and the lower-GI tract in vivo. The work assessed the feasibility of performing in vivo microscopy at endoscopic examination and evaluated fluorescence imaging protocols.

METHODS

Images were collected in real time by using two prototype endoscope configurations, featuring slightly different miniaturized fiber-optic confocal microscopes, fitted integrally into the tips of conventional endoscopes. Confocal scanning was performed at 488 nm illumination for excitation of exogenously applied fluorophores (topical acriflavine and intravenous fluorescein). The images were compared with conventional histology of biopsy specimens and the findings of white-light endoscopy.

RESULTS

Confocal endomicroscopy enabled imaging of cellular and subcellular structures (i.e., nuclei) of the GI tract. The crypts of the colonic mucosa, the villi of the terminal ileum and duodenum, the gastric pits of the stomach, and the squamous epithelium of the distal esophagus could be clearly visualized. Acriflavine strongly contrasted the cell nuclei of the surface epithelium, including the absorptive epithelial cells and the mucous secreting goblet cells. Fluorescein stained the extracellular matrix of the surface epithelium and also the subepithelial layers of the lamina propria. Images at increasing depth beneath the epithelium showed the mucosal capillary network. The findings correlated with the histology of biopsy specimens.

CONCLUSIONS

The development of a fluorescence confocal endomicroscope makes it practical to examine the upper- and the lower-GI mucosa in cellular detail during otherwise routine endoscopic examination. The results represent a major technical advance in the development of this new optical imaging modality for the in vivo examination of GI tissue.

Confocal laser endomicroscopy

A miniaturized confocal microscope was developed that could be integrated in the distal tip of a conventional colonoscope. With this technique, denoted confocal endomicroscopy, subsurface analysis of the gut mucosa and in-vivo histology during ongoing endoscopy are possible in full resolution by point scanning laser analysis. The diagnostic spectrum of confocal endomicroscopy is expanding from screening and surveillance for colorectal cancer to Barrett's esophagus, Helicobacter pylori-associated gastritis, and gastric cancer. The new detailed images seen with confocal laser endomicroscopy allow a unique look on cellular structures at and below the surface of the gut. This review describes the optical and diagnostic possibilities of confocal laser endomicroscopy.

Short term arterial remodelling in the aortae of cholesterol fed New Zealand white rabbits shown in vivo by high-resolution magnetic resonance imaging — implications for human pathology

High-resolution, non-invasive imaging methods are required to monitor progression and regression of atherosclerotic plaques. We investigated the use of MRI to measure changes in plaque volume and vessel remodelling during progression and regression of atherosclerosis in New Zealand White rabbits. Atherosclerotic lesions were induced in the abdominal aorta by balloon injury and cholesterol feeding. MR images (2D) of the abdominal aorta were acquired with cardiac and respiratory gating using a fast spin echo sequence with and without fat-suppression. In an initial study on rabbits treated for 30 weeks we imaged the aortae with a spatial resolution of 250x250 micrometers with a slice thickness of 2 mm and achieved a close correlation between MRI-derived measurements and those made on perfusion pressure-fixed histological sections (r(1) = 0.83, slope p(1) < 0.01). We subsequently imaged 18 rabbits before and periodically during 12 weeks of cholesterol feeding (progression) followed by 12 weeks on normal diet (regression). Aortic wall (atherosclerotic lesion) volume increased significantly during progression and decreased during regression. In contrast, lumen volume increased during progression and did not change during regression. In conclusion, this study confirms that non-invasive, high-resolution MRI can be used to monitor progression and regression of atherosclerosis, each within 3 months and shows, for the first time in a short-term model, that positive remodelling occurs early during progression and persists through regression of atherosclerotic lesions.

Optical coherence tomography of malignancy in hamster cheek pouches

Optical coherence tomography (OCT)/optical Doppler tomography (ODT) provides real-time in vivo high-resolution (10-microm) imaging of tissues and real-time spatially resolved blood flow in microvasculature. Hamster cheek pouches with induced dysplasia and malignancies were imaged with OCT/ODT to assess the potential for application to airway malignancy. In 22 Golden Syrian hamsters, 0.5% 9,10-dimethyl-1,2-benzanthracene induces carcinogenesis over 10 weeks in right side cheek pouches; the left side three served as controls. The cheek pouches are imaged in vivo prior to sacrifice, and in vitro after excision, using a prototype 1310-nm broadband superluminescent diode based OCT/ODT device. Images are compared to standard histopathology. OCT imaging offers good resolution of the hamster cheek pouches to depths of 1 to 3 mm and paralleled histologic images. The feasibility of high-resolution functional imaging is demonstrated in this hamster cheek pouch tumor model. ODT accurately detects vascular change associated with carcinogenesis.

Imaging of small vessels using photoacoustics: An in vivo study

BACKGROUND AND OBJECTIVES

The ability to correctly visualize the architectural arrangement of microvasculature is valuable to many diverse fields in medicine. In this study, we applied photoacoustics (PA) to obtain high-resolution images of submillimeter blood vessels.

STUDY DESIGN/MATERIALS AND METHODS

Short laser pulses are used to generate ultrasound from superficial blood vessels in several animal models. From these ultrasound waves the interior of blood vessels can be reconstructed.

RESULTS

We present results from a novel approach based on the PA principle that allows specific in vivo visualization of dermal blood vessels without the use of contrast agents or ionizing radiation.

CONCLUSIONS

We show PA images of externalized blood vessels and demonstrate in vivo PA imaging of vasculature through layers of skin varying in thickness.

View of Normal Human Skin In Vivo as Observed Using Fluorescent Fiber-Optic Confocal Microscopic Imaging

Fluorescence confocal scanning laser microscopy, using a miniaturized handheld scanner, was performed to visualize the microscopic architecture of normal human epidermis in vivo. Fluorescein sodium (approximately 20 microL of 0.2% wt/vol) was administered via intradermal injection to normal skin on the volar forearm of 22 patients. The skin was imaged continuously from 1 to 15 min after injection. Fluorescein was excited at 488 nm and the fluorescent emission was detected at > 505 nm. In each subject, a series of images was collected at increasing depth, from superficial stratum corneum to papillary dermis. Features observed in confocal images were compared to those seen in hematoxylin- and eosin-stained sections of skin. The confocal images demonstrated the architecture of superficial skin in the horizontal plane. There was a transition in keratinocyte size, shape, and morphology with progressive imaging into the deeper epidermal layers. Superficial dermis and microscopic capillaries with blood flow were easily observed. The morphologic patterns associated with the major cell types of the epidermis were consistent with those known from conventional histology. We report the ability of in vivo fluorescence point scanning laser confocal microscopy to produce real-time, high-resolution images of the microscopic architecture of normal human epidermis using a noninvasive imaging technology.

Confocal laser scanning microscopy of urinary bladder after intravesical instillation of a fluorescent dye

OBJECTIVES

To assess the potential of confocal laser scanning microscopy for imaging of the urinary bladder after intravesical instillation of a fluorescent dye.

METHODS

The study was performed on the bladder of male Copenhagen rats. For confocal fluorescence microscopy (CFM), a standard confocal laser scanning microscope (Zeiss LSM 410) was used. Before measuring, the fluorescent marker SYTO 17 was instilled intravesically. After 2 hours of incubation, the rat was killed, the bladder excised and opened, and CFM was performed starting from the surface going through the urothelium and superficial layers of the lamina propria. Except for the opening incision, the bladder was left intact and no biopsies were taken. After imaging, the bladder was sent for conventional histologic studies.

RESULTS

CFM allows imaging of cellular details of the entire urothelium (superficial umbrella cells, intermediate, and basal urothelial cells) and superficial layers of the lamina propria. CFM images are close to those obtained by standard microscopy after conventional hematoxylin-eosin staining. Cell structure (eg, shape, size, chromatin texture, nucleoli, mitotic figures, nuclear/cytoplasmic ratio), as well as the structure of the connective tissue (eg, collagen fibers, blood vessels, erythrocytes), can be studied, allowing a standard histologic evaluation. Furthermore, in contrast to conventional histologic evaluation, CFM provides three-dimensional information and allows the study of intact tissue representing the true in vivo situation.

CONCLUSIONS

CFM enables the study of the microscopic anatomy of bladder mucosa in its in vivo state. In combination with optical fiber bundles, endoscopic microscopy of the bladder may be possible in the future.

Surface analysis methods for characterizing polymeric biomaterials

Surface properties have an enormous effect on the success or failure of a biomaterial device, thus signifying the considerable importance of and the need for adequate characterization of the biomaterial surface. Microscopy techniques used in the analysis of biomaterial surfaces include scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and confocal microscopy. Spectroscopic techniques include X-ray photoelectron spectroscopy, Fourier Transform infrared attenuated total reflection and secondary ion mass spectrometry. The measurement of contact angles, although one of the earlier techniques developed remains a very useful tool in the evaluation of surface hydrophobicity/hydrophilicity. This paper provides a brief, easy to understand synopsis of these and other techniques including emerging techniques, which are proving useful in the analysis of the surface properties of polymeric biomaterials. Cautionary statements have been made, numerous authors referenced and examples used to show the specific type of information that can be acquired from the different techniques used in the characterization of polymeric biomaterials surfaces.

Fluorescence lifetime imaging of unstained tissues: early results in human breast cancer

Fluorescence lifetime imaging (FLIM) depends on the fluorescence decay differences between tissues to generate image contrast. In the present study FLIM has been applied to fixed (but unstained) breast cancer tissues to demonstrate the feasibility of this approach for histopathological assessment. As the FLIM method relies on natural autofluorescence, it may be possible to circumvent tissue processing altogether and so FLIM has the potential to be a powerful new method of in vivo tissue imaging via an endoscopic or per-operative approach in a variety of organs, as well as a research tool for in vivo animal models of disease. Unstained, alcohol-fixed tissue samples from 13 patients were stimulated by laser pulses at 415 nm. The temporal decay of the autofluorescence was imaged over a period of 2 ns after cessation of the pulse. The decay rate at each image pixel was calculated as the 'lifetime' factor tau. A tissue classification scheme was used to define regions in each image. The average lifetimes of different tissue regions were compared. A total of 167 tissue regions were measured. Within individual fields, stroma had a larger tau (slower decay) than epithelium (p < 0.001). Within individual patients (taking the mean tau of a given tissue type across all fields from each patient), there was a statistically significant difference between benign and malignancy-associated stroma (p < 0.05). Also, benign collagen had a longer tau than benign epithelium (p < 0.05). Multivariate analysis showed a significant difference between benign stroma, malignancy-associated stroma, blood vessels, and malignant epithelium (p < 0.05). Statistically significant differences between benign and malignancy-associated stroma were obtained even with small patient numbers, indicating that lifetime-based instruments can be developed for real-time diagnostic imaging with microscopic resolution.

In vivo detection of small subsurface melanomas in athymic mice using noninvasive fiber optic confocal imaging

Fiber optic confocal imaging, following intravenous administration of fluorescently labeled antibodies and Texas Red-dextran, enabled in vivo detection of melanoma and surrounding blood vessels in athymic mice. Human melanoma cells (three cell lines) and cultured normal human skin cells were implanted intradermally into the haunch skin of anesthetized athymic BALB/C mice and allowed to grow to a maximum size of 2 mm diameter. Using three different fluorescein-isothiocyanate-labeled antimelanoma antibodies, single channel confocal images of melanoma cells were obtained in vivo. Using noninvasive techniques, the overall in vivo melanoma detection rate for tumors within 0.2 mm of the skin surface was 84% (27 of 32 tumors). Normal cultured human skin cells were found to have little or no fluorescence after administration of the fluorescein-isothiocyanate-labeled antibodies and tumors were not labeled by an isotype control antibody. Dual channel imaging of the implanted melanoma tumor and surrounding dermal vasculature in vivo showed increased blood vessel density at the melanoma site. Conventional immunoperoxidase histology confirmed that fiber optic confocal imaging was able to detect melanoma tumors up to 0.2 mm below the skin surface, in vivo.