Three-dimensional simultaneous optical coherence tomography and confocal fluorescence microscopy for investigation of lung tissue

Ventilation and Perfusion at the Alveolar Level: Insights From Lung Intravital Microscopy

Intravital microscopy (IVM) offers unique possibilities for the observation of biological processes and disease related mechanisms in vivo. Especially for anatomically complex and dynamic organs such as the lung and its main functional unit, the alveolus, IVM provides exclusive advantages in terms of spatial and temporal resolution. By the use of lung windows, which have advanced and improved over time, direct access to the lung surface is provided. In this review we will discuss two main topics, namely alveolar dynamics and perfusion from the perspective of IVM-based studies. Of special interest are unanswered questions regarding alveolar dynamics such as: What are physiologic alveolar dynamics? How do these dynamics change under pathologic conditions and how do those changes contribute to ventilator-induced lung injury? How can alveolar dynamics be targeted in a beneficial way? With respect to alveolar perfusion IVM has propelled our understanding of the pulmonary microcirculation and its perfusion, as well as pulmonary vasoreactivity, permeability and immunological aspects. Whereas the general mechanism behind these processes are understood, we still lack a proper understanding of the complex, multidimensional interplay between alveolar ventilation and microvascular perfusion, capillary recruitment, or vascular immune responses under physiologic and pathologic conditions. These are only part of the unanswered questions and problems, which we still have to overcome. IVM as the tool of choice might allow us to answer part of these questions within the next years or decades. As every method, IVM has advantages as well as limitations, which have to be taken into account for data analysis and interpretation, which will be addressed in this review.

Gabor domain optical coherence microscopy combined with laser scanning confocal fluorescence microscopy

We report on the development of fluorescence Gabor domain optical coherence microscopy (Fluo GD-OCM), a combination of GD-OCM with laser scanning confocal fluorescence microscopy (LSCFM) for synchronous micro-structural and fluorescence imaging. The dynamic focusing capability of GD-OCM provided the adaptive illumination environment for both modalities without any mechanical movement. Using Fluo GD-OCM, we imaged ex vivo DsRed-expressing cells in the brain of a transgenic mouse, as well as Cy3-labeled ganglion cells and Cy3-labeled astrocytes from a mouse retina. The self-registration of images taken by the two different imaging modalities showed the potential for a correlative study of subjects and double identification of the target.

In vivo imaging of murine vasodynamics analyzing different mouse strains by optical coherence tomography

BACKGROUND AND AIMS

We tried to circumvent the limitations of standard organ chamber experiments using in vivo optical coherence tomography (OCT) to analyze the vascular function of small arteries in different mouse strains.

METHODS

OCT images were acquired with a two-axis galvanometer scanner head. Time series (3 frames per second, 300 × 512 pixel per frame) of cross-sectional images were analyzed with image processing software measuring the time course of vessel lumen dynamics. Vascular function of murine saphenous artery of male C57BL/6 (wild-type) and hypercholesterolemic LDLR knockout (LDLR^-/-) mice was analyzed at 6 weeks and after 14 weeks feeding a control or high-fat diet containing 21.2% butter fat and 2.1 mg/kg cholesterol. Vasoconstriction and vasodilation was analyzed by OCT in response to 80 mM K⁺ and 1 mM SNP.

RESULTS

The OCT technique allowed determination of inner diameter, flow resistance, maximal velocity of diameter change and time to half-maximal diameter change in murine saphenous arteries of wild-type and LDLR^-/- mice. LDLR^-/- had impaired vasodilation and changes in vasodynamics after 14 weeks on control or high-fat diet, compared to wild-type mice. The diameter of the saphenous artery of LDLR^-/- mice was reduced after vasoconstriction (38 ± 7 μm vs 12 ± 6 μm) and vasodilation (245 ± 8 μm vs 220 ± 10 μm) (P < 0.05 vs C57BL/6).

CONCLUSION

OCT was used as an innovative method to image vascular function of small arteries of wild-type and hypercholesterolemic LDLR^-/- mice after high-fat diet. The method offers the ability to display differences in the vasodynamics at early stages of endothelial dysfunction in vivo.

Toward in vivo two-photon analysis of mouse aqueous outflow structure and function

The promise of revolutionary insights into intraocular pressure (IOP) and aqueous humor outflow homeostasis, IOP pathogenesis, and novel therapy offered by engineered mouse models has been hindered by a lack of appropriate tools for studying the aqueous drainage tissues in their original 3-dimensional (3D) environment. Advances in 2-photon excitation fluorescence imaging (TPEF) combined with availability of modalities such as transgenic reporter mice and intravital dyes have placed us on the cusp of unlocking the potential of the mouse model for unearthing insights into aqueous drainage structure and function. Multimodality 2-photon imaging permits high-resolution visualization not only of tissue structural organization but also cells and cellular function. It is possible to dig deeper into understanding the cellular basis of aqueous outflow regulation as the technique integrates analysis of tissue structure, cell biology and physiology in a way that could also lead to fresh insights into human glaucoma. We outline recent novel applications of two-photon imaging to analyze the mouse conventional drainage system in vivo or in whole tissues: (1) collagen second harmonic generation (SHG) identifies the locations of episcleral vessels, intrascleral plexuses, collector channels, and Schlemm's canal in the distal aqueous drainage tract; (2) the prospero homeobox protein 1-green fluorescent protein (GFP) reporter helps locate the inner wall of Schlemm's canal; (3) Calcein AM, siGLO™, the fluorescent reporters m-Tomato and GFP, and coherent anti-Stokes scattering (CARS), are adjuncts to TPEF to identify live cells by their membrane or cytosolic locations; (4) autofluorescence and sulforhodamine-B to identify elastic fibers in the living eye. These tools greatly expand our options for analyzing physiological and pathological processes in the aqueous drainage tissues of live mice as a model of the analogous human system.

Murine bladder imaging by 2-photon microscopy: an experimental study of morphology

PURPOSE

We developed 2-photon laser scanning microscopy analysis of the native murine bladder.

MATERIALS AND METHODS

Bladder tissue from wild-type mice was imaged by 2-photon laser scanning microscopy autofluorescence and second harmonic generation microscopy. Bladder wall layers and structures were analyzed using differences in color, size, shape and morphology.

RESULTS

Autofluorescence of the urothelium, nerve structures and muscles was visible in the green spectral channel due to autofluorochromes such as NAD(P)H and elastin. Second harmonic generation of collagen was seen in the blue spectral channel. Imaging from the mucosal side revealed umbrella cells at 0 and 30 μm, of which the high cellular NAD(P)H content allows autofluorescence detection. Below that a network-like connective tissue layer was visualized up to 50 μm that contained vessels with a diameter of 10 to 40 μm and nerves with a diameter of 1 to 6 μm. Imaging from the adventitial side revealed a radiant collagen layer covered with nerves and macrophages at 0 to 20 μm. Below at 20 to 25 μm we visualized a thick muscle layer containing elastic fibers and macrophages. Findings were also represented in 3-dimensional reconstructions, providing information on structure localization, orientation and interconnection.

CONCLUSIONS

Two-photon laser scanning microscopy imaging using autofluorescence of the murine bladder is a promising technique to provide new insight into structures and morphology. It opens avenues to identify structural changes in bladder pathology.

Advances and future directions in interventional pulmonology

The term "interventional pulmonology" (IP) supersedes the previously used term "thoracic endoscopy," a change that reflects the evolution of a specialty devoted to performing highly sophisticated and technologically advanced procedures in the lungs and chest. Continuing advances in technology promise to further expand IP's diagnostic and therapeutic frontiers. However, standardized educational programs to train and test IP physicians will be essential to maintain a high standard of practice in the field.