Probe-based intravital microscopy: filling the gap between in vivo imaging and tissue sample microscopy in basic research and clinical applications

Non- and minimally invasive imaging technologies have become indispensable in preclinical studies using animal models to understand biological processes and assess novel therapeutic strategies within the complex context of living organisms. Various imaging modalities can provide anatomical, functional or molecular information on the organ- or whole-body level, however, there exists a need to obtain dynamic information on the microscopic level in living animals to bridge the gap with microscopical analysis of processed tissues. To fulfill this need, intravital microscopy (IVM), which allows imaging at cellular and subcellular resolution in living animals, was developed. The emergence of different imaging modalities, advances in fluorescent labeling methods and the transition from optical windows to fiber-optical probes to obtain direct access to sites deep inside the animal, have supported its widespread use. This review provides an overview of these technological advancements and specifically of the application of fibered confocal fluorescence microscopy in preclinical research. In addition, the implementation of probe-based confocal laser scanning endomicroscopy in clinical research on gastrointestinal and lung diseases and possible applications in drug development are described. Finally, drawbacks and possible advances that can broaden the potential of this technique and what can be learnt from IVM in a context of multimodal imaging are highlighted.