Fluorescence-based molecular imaging in small animals is having a major impact on drug development and disease research. However, a significant challenge to imaging targeted fluorescent markers in vivo remains: unless the labeled regions are located superficially; localization, quantitation and host organ identification are impeded by the effects of light scattering and absorption. Orthotopic tumor and disease models are increasingly preferred over less biologically relevant subcutaneous xenografts. In such studies, substantial difficulties are encountered in longitudinal studies where animals are growing and are positioned differently for each measurement. We offer DyCETM, dynamic contrast enhancement, the imaging advance that will address these issues and radically advance the utility of in vivo molecular imaging by providing anatomical co-registration of labeled markers by exploiting in vivo pharmacokinetics of dyes in small animals in a simple and inexpensive way.
By acquiring a time-series of optical images following a bolus injection of an inert near-infrared dye indo cyanine green (ICG), we can repeatably and accurately delineate the major internal organs of mice using optical imaging alone. This is possible because each organ has a characteristic pharmacodynamic uptake or distribution pattern that can be “illuminated” by the kinetics of dye passing through it to make it distinguishable from other structures. Subsequently, spatiotemporal analysis can exploit these characteristic patterns to allow the body-surface representation of each organ to be visualized. These in vivo anatomical maps can be overlaid onto simultaneously acquired images of a targeted molecular probe (detected and distinguished from the mapping dye via multispectral imaging techniques) to significantly aid in identification of the marker's anatomical and physical location.
DyCE can be applied singly or in combination with functionalized marker probes. Multispectral capabilities are critical here, since the validity of the simple optical triangulation method for signal colocalization requires that the molecular marker probe and the organmapping dye have similar optical properties. Dyes with similar optical properties will require spectral tools for separating them, the core capability of CRi's Maestro product line. If multiplexing is desired as well in the favored near-infrared (NIR) region, this enforces the need for multispectral techniques. These techniques enhance the imaging sensitivity by eliminating the ubiquitous autofluorescence signals from the targeted marker probes. In addition, CRi's multispectral analysis tools have shown utility in analyzing the data by treating the time courses like spectral information.
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