In the current study by Leblond et al. the sensitivity of an FMT system for preclinical small animal imaging is systematically quantified. The FMT system in the current study is coupled to a small-animal computed tomography system and employs photomultiplier tubes (PMT) for photon detection enabling single-photon counting. Studies using tissue-simulating phantoms are completed to assess the effects of both tissue thickness and fluorophore concentration on detected signal using the single-photon counting FMT system. Using Alexa Fluor 647, it was shown the concentrations as low as 1 nM could be detected through more than 5 cm of tissue. As a general rule, phantom studies illustrated that for every 1 cm increase in tissue thickness an order of magnitude decrease in fluorophore concentration could be detected. Studies were also conducted using a 10 nM solution of IRdye800 in a 5-mm-diameter tube inserted through a cadaverous rat to illustrate the sensitivity of the FMT system. The studies presented here suggest that subnanomolar concentrations of near-infrared fluorophores can be detected in preclinical mouse and rat models of disease. This capability will enable significantly better noninvasive detection and quantification of targeted fluorophores to diseased tissues such as orthotopically implanted model tumor tissues than conventional reflectance fluorescence imaging.
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