In vivo imaging of murine endocrine islets of Langerhans with extended-focus optical coherence microscopy

Abstract

Aims/hypothesis Structural and functional imaging of the islets of Langerhans and the insulin-secreting beta cells represents a significant challenge and a long-lasting objective in diabetes research. In vivo microscopy offers a valuable insight into beta cell function but has severe limitations regarding sample labelling, imaging speed and depth, and was primarily performed on isolated islets lacking native innervations and vascularisation. This article introduces extended-focus optical coherence microscopy (xfOCM) to image murine pancreatic islets in their natural environment in situ, i.e. in vivo and in a label-free condition.Methods Ex vivo measurements on excised pancreases were performed and validated by standard immunohistochemistry to investigate the structures that can be observed with xfOCM. The influence of streptozotocin on the signature of the islets was investigated in a second step. Finally, xfOCM was applied to make measurements of the murine pancreas in situ and in vivo. Results xfOCM circumvents the fundamental physical limit that trades lateral resolution for depth of field, and achieves fast volumetric imaging with high resolution in all three dimensions. It allows label-free visualisation of pancreatic lobules, ducts, blood vessels and individual islets of Langerhans ex vivo and in vivo, and detects streptozotocin-induced islet destruction. Conclusions/interpretation Our results demonstrate the potential value of xfOCM in high-resolution in vivo studies to assess islet structure and function in animal models of diabetes, aiming towards its use in longitudinal studies of diabetes progression and islet transplants.

Longitudinal three-dimensional visualisation of autoimmune diabetes by functional optical coherence imaging

“…As we have previously shown, xfOCM imaging can be used to identify pancreatic islets in surgically exposed pancreases of live animals; the strong light scattering observed correlates strongly with insulin-producing beta cells [17]. As OCM is sensitive to changes in refractive index and because pancreatic beta cells have a high zinc content [27], we hypothesised that the origin of the strong OCM signal is dominantly caused by the zinc-insulin crystals in the pancreatic beta cells.…”

“…This intrinsic multiplex advantage results in a fast parallel acquisition of entire depth profiles without depth scanning, with an in vivo penetration depth of ∼300 μm in the pancreas. However, optical pancreas imaging requires laparotomy, restricting this technique to transversal studies [17][18][19]. Recently, the anterior chamber of the eye (ACE) has been used to study transplanted pancreatic islets [20][21][22].…”

Reporter islets in the eye reveal the plasticity of the endocrine pancreas

“…In vitro techniques include the analysis of histological sections of pancreas by point counting morphometry (19) and the direct measurements of islet dimensions in dissected pancreatic tissue (24,25). Ex vivo imaging techniques involve the imaging of exteriorized pancreas by confocal microscopy (26) or optical coherence microscopy (27). Finally, several noninvasive in vivo imaging techniques aim to longitudinally quantify total beta cell mass, including magnetic resonance imaging (28), positron emission tomography (29), bioluminescence imaging (30), and combined multimodal imaging (31).…”

Label-Free Imaging of Cerebral β-Amyloidosis with Extended-Focus Optical Coherence Microscopy

“…However, the lateral resolution is given by the numerical aperture (NA) of the objective, thereby creating a trade-off between transverse resolution and focal range. To circumvent this trade-off, we have developed an extended-focus version of OCT (extended-focus Fourier domain optical coherence microscopy; xfOCM) that exhibits uniformly high transverse resolution along an extended focal range (Leitgeb et al, 2006;Villiger et al, 2009). To this end, a Bessel-mode instead of the traditional Gaussian mode illumination beam is used (Leitgeb et al, 2006;Villiger et al, 2009).…”

“…To circumvent this trade-off, we have developed an extended-focus version of OCT (extended-focus Fourier domain optical coherence microscopy; xfOCM) that exhibits uniformly high transverse resolution along an extended focal range (Leitgeb et al, 2006;Villiger et al, 2009). To this end, a Bessel-mode instead of the traditional Gaussian mode illumination beam is used (Leitgeb et al, 2006;Villiger et al, 2009). Additionally, Bessel beams exhibit a self-reconstructing capability, making them particularly interesting for deep imaging into scattering tissues (Fahrbach et al, 2010).…”