Development and testing of multi-modal, multi-scale imaging systems for rare-earth-doped contrast agents
Creators: name: Higgins, Laura
Publisher: name: No Publisher Supplied
Year: 2016

description: Rare-earth based nanoparticles have appealing properties for use as contrast agents in biomedical imaging. With unique luminescent properties and a refractive index that is higher than that of tissue, these versatile materials have a wide range of potential applications spanning basic science research to preclinical testing and clinical translation. The goal of this dissertation was to exploit the unique optical properties of these materials to develop new multi-modal, multi-scale imaging platforms and expand the applicability of these materials in biomedicine.  Under near-infrared excitation, these particles emit conventional Stokes-shifted fluorescence in the short wave infrared region (SWIR), as well as a higher-energy upconversion signal in the visible spectrum. Previous work, focused on wide-field imaging of the SWIR fluorescence, has shown the ability to detect the accumulation of biofunctionalized rare-earth albumin nanocomposites (fREANCs) in preclinical models of cancer metastasis. This dissertation builds upon previous studies, exploring high- resolution imaging of these particles to serve as an â€œoptical biopsyâ€  through the combination of confocal microscopy and optical coherence tomography (OCT). Confocal microscopy provides subcellular resolution imaging from near the tissue surface while OCT is capable of imaging tissue microstructure up to 1-2 mm below the surface, both important factors in the evaluation of disease progression.  High-resolution imaging of these materials in thick tissues has been limited by the long emission lifetimes of the rare-earth elements. This work demonstrates that line- scanning confocal microscopy (LSC) can overcome these challenges by extending the excitation and emission time while maintaining frame rate, providing a method for real- time, high-resolution imaging of rare-earth doped contrast agents in ex vivo tissue samples. Although the refractive index mismatch did not increase OCT backscattering in tissue, motivating the development of fREANCs as a molecularly-targeted OCT contrast agent, OCT can still provide valuable insight into tissue disease state based on native optical properties.  From this work, a multi-modal imaging platform was developed combining OCT with line-scanning confocal microscopy of fREANCs. A first-generation proof-of-concept system, combining OCT with full-field fluorescence microscopy allowed for the identification of potential technical challenges, before integrating OCT within the line- scanning microscope. Through the combination of LSC and OCT, the second-generation system achieved an en face lateral resolution of 2.8 Î¼m (LSC) with an imaging depth of 1.4 mm (OCT). Finally, this multi-modal imaging platform was evaluated within a preclinical study, designed to explore multi-scale imaging of fREANCs to identify tumors in the lungs. Through this work, signature features of healthy and malignant tissue were identified within the multi-modal image sets, with the potential to serve as a basis for future high-resolution in vivo imaging as a method of â€œoptical biopsyâ€  in the presence of fREANCs. More generally, the technical development of multi-scale, multi-modal imaging presented here, ranging from the macroscopic to microscopic scale, may be beneficial across a broad range of emerging applications for rare-earth based nanoscale contrast agents.