Quantitative real-time catheter-based fluorescence molecular imaging in mice.

PURPOSE: To prospectively evaluate an optical imaging system designed to perform quantitative, intravital catheter-based imaging of fluorescent molecular probes.
MATERIALS AND METHODS: This study was performed according to a protocol approved by the institutional animal care committee. A fiberoptic catheter imaging system was developed to implement a normalization algorithm for real-time quantitative near-infrared (NIR) imaging. The system was validated with in vitro imaging of fluorochrome phantoms and in vivo fluorescence measurements obtained in tumors implanted in murine abdomens (n = 7) after administration of an enzyme-activatable NIR probe. Standard analysis of variance tests were used to determine significant dissimilarities in signal from distinct fluorochrome concentrations. The clinical utility of the system was further evaluated by imaging orthotopically implanted murine colonic adenocarcinomas (n = 4).
RESULTS: Raw NIR fluorescence intensities, which were measured with a fiberoptic catheter placed above wells of varying NIR fluorochrome concentration, varied markedly (>100%) with catheter position, while the corrected NIR signal was confined to a range of values within 10% of their mean for each individual fluorochrome concentration and were significantly distinct (P < .001) between relevant concentration ranges. Similar results were observed for the in vivo measurements from the abdominally implanted tumors, with raw NIR signal varying 20% from the mean and corrected NIR signal varying only 1% from the mean. The colonic studies revealed that the correction method was robust enough for use during minimally invasive imaging procedures.
CONCLUSION: The authors have developed and implemented a method for quantitative real-time catheter-based fluorescence imaging that resolves NIR signal dependence on changes in catheter position.