Multimodal Imaging Platforms

For noninvasive, high-resolution and in vivo structural and molecular imaging (with 0.8-20 μm resolution and 0.2- 2 mm imaging depth)

OCT + Single-photon Excited Fluorescence Imaging

OCT is a noninvasive high-resolution (2-20 μm) imaging technology capable of visualizing architectural morphologies of biological tissue; but it generally lacks specificity. In comparison, fluorescence imaging provides molecular specificity which complements OCT. In 2012 we reported an all-fiber-optic multimodal OCT and fluorescence imaging platform for endoscopic imaging. Our probe featured a distal scanning mechanism with an outer diameter of 2.4mm and a rigid length of ~ 14 mm.

Figure 1. Schematic of the dual-modality system capable of performing endoscopic OCT and fluorescence imaging simultaneously. See more details in J. Mavadia, et. al., Biomed Opt. Express 13 (2012) (Click to enlarge and view detailed caption)

There are several technical challenges associated with such a multimodal system. Some major challenges include fiber optic single-mode delivery of the OCT source light and fluorescence excitation light to the sample, recollecting the OCT and fluorescence emission light from the sample, and finally separating the backscattered OCT light from the fluorescence emission, plus methods of performing circumferential beam scanning. Our research is dedicated to solving these technical issues and translating the multimodal endoscopy technology to in vivo applications.

Figure 2. Circumferential scanning and pull back were performed to obtain 3D volumetric OCT images and 2D fluorescence surface map of the esophagus with the endoscope. See more details in J. Mavadia, et. al., Biomed Opt. Express 13 (2012)(Click to enlarge and view detailed caption)

OCT + Two-photon Excited Fluorescence

OCT is capable of visualizing tissue structural morphologies with a few millimeter imaging depth. The major pitfall of the OCT technology is the lack of molecular specificity. In comparison, two-photon fluorescence (TPF), in addition to the superb spatial resolution, offers excellent sensitivity to endogenous or exogenous fluorescent molecules, providing local biochemical or metabolic information about biological tissues which cannot be obtained by OCT; however its imaging depth is limited to a few hundred microns. OCT and two-photon fluorescence imaging thus provides complementary information, and the combination of the two offers unique capabilities for performing noninvasive of "optical biopsy" near or at true histology resolution. l. In 2012 we reported a multimodal OCT and TPF endoscopic imaging platform. Our probe featured a forward scanning mechanism with an overall outer diameter of 2.8mm. The resolutions were ~2.5 × 10.0 μm (lateral × axial) in air for OCT and ~1.2 × 5.7 μm (lateral × axial) for TPF imaging.

Figure 3. Schematic of TPF/OCT multimodal endomicroscope system. See more details in J. F. Xi, et. al., Opt. Lett. 37 (2012) (Click to enlarge and view detailed caption)



Figure 4. OCT, TPF and superposed images of mouse adipose tissue with local ICG administration. See more details in J. F. Xi, et. al., Opt. Lett. 37 (2012) (Click to enlarge and view detailed caption )



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