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Assessment of fluorescently-labeled gold nanoparticles in mice as a contrast agent for micro-computed tomography and optical projection tomography Kozomara, Stevo

Abstract

Objectives: Contrast agents are required to be able to view and differentiate tissues in 3-D computed tomography (CT) due to similarities in density. Pre-clinical contrast agents used for radiology are not visible when viewed histologically, and visa versa. Identifying a single agent that is visible in both x-ray and optical imaging, would ensure that the target tissues can be easily identified and correlated in both images, without the need of additional staining techniques. Here we present an approach for imaging the murine cardiovascular system and organs, and melanoma tumours using micro-computed tomography (micro-CT) and optical projection tomography (OPT), using fluorescently-labeled gold nanoparticles. Materials and Methods: A 1% agarose phantom was used with 2 µl of the Cy3 fluorescently-labeled gold nanoparticles deposited in the block, and imaged with micro-CT and OPT. In vivo systemic testing involved tail vein intravascular injections into mice using Cy3 fluorescently-coated gold nanorods. These mice were subjected to micro-CT scans, both before and after contrast injection. Once euthanized, the heart, liver and kidneys were excised, scanned using the higher resolution specimen micro-CT scanner, then prepared, and visualized under OPT using filtered UV light at 545-610nm. Localized in vivo testing was performed using B16F10 cells to induce tumour growth in the right hind legs of mice. Cy3 fluorescently-coated gold nanorods were injected directly into the tumours prior to imaging. The mice were scanned with in vivo micro-CT for pre- and post-contrast scans. Once euthanized, the hind leg was dissected and scanned with a specimen micro-CT at a higher resolution. The dissected hind legs were prepared and visualized under OPT using filtered UV light at 545-610 nm. Results: Using the agarose phantom, the gold nanoparticles were visible under both micro-CT and OPT, with co-localization between images. With the in vivo systemic testing, the nanoparticles were not visible. The in vivo localized tumour study showed the distribution of the gold nanoparticles within the tumours, allowing for visualization under micro-CT. OPT imaging was successful and co-localized to micro-CT. Conclusions: Cy3 fluorescently-labeled gold nanorods injected into murine melanoma tumours can be visualized under micro-CT imaging, and co-localized to OPT.

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