Toward whole-body optical imaging of rats using single-photon counting fluorescence tomography
Spotlight summary: Fluorescence imaging is a widely used technology both in preclinical and clinical applications. The most routinely utilized fluorescence imaging systems use reflectance-based imaging technology, in which both the excitation light source and the emission collect device, usually a CCD, reside on the same side of the subject. Although relatively easy to use, the reflectance-based fluorescence imaging systems provide inherently surface-weighted information. When the fluorescent object of interest is located at any depth within the sample, quantification using fluorescence reflectance-based imaging will be inaccurate. This is especially apparent in preclinical mouse models in which quantification of intensity in internal fluorescence structures is desired. Fluorescence molecular tomography (FMT), which collects measurements from around the structure of interest, such as a mouse, can provide quantitative fluorescence intensity data. With the use of FMT, the entire tissue is interrogated by the excitation light, enabling readout from fluorophore relatively deep within the tissue in comparison to reflectance fluorescence imaging. However, one of the disadvantages of FMT is its sensitivity to low fluorophore concentration. Even though the tissue may be fully interrogated with excitation light, weak fluorescence emission signals emanating from low concentrations of deep-seated fluorophore may not be detected.
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.
Technical Division: Optics in Biology and Medicine
ToC Category: Medical Optics and Biotechnology
|OCIS Codes:||(170.5280) Medical optics and biotechnology : Photon migration|
|(300.6280) Spectroscopy : Spectroscopy, fluorescence and luminescence|
|(110.4234) Imaging systems : Multispectral and hyperspectral imaging|
|(170.6935) Medical optics and biotechnology : Tissue characterization|
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