Depth Resolved Quantification of Fluorescence in Skin

The ability to quantify fluorescence can be useful for understanding the motility of topically applied fluorescing drugs as well as dosimetry planning for light-based therapies like photodynamic therapy (PDT). Previously we have reported a quantitative imaging approach using a Spatial Frequency Domain Imaging (SFDI) technique that can extract bulk drug concentration from skin based on its fluorescent signal. This method, however, assumes that the drug is homogenously distributed within the tissue volume probed.

In this project, we are developing several modified approaches that apply this SFDI approach to tissue where the fluorophore distributions vary in depth.  We are exploring light transport model based approaches that characterize the spectral absorption and scattering properties in tissue in order to better understand and interpret the fluorescent signal generated within the tissue volumes. To extract depth information, we additionally exploit both spectrally selective depth penetrance of multiple excitation sources as well as spatial frequency dependent depth sensitivity from both excitation and emission wavelengths.

(Left): Photo of healthy skin, within the ink markers is where topical ALA is applied; (middle): wide-field image of topical drug distribution in vivo; (right): quantitative drug penetration and distribution into tissue, 5 hours after topical application  

The primary objectives of these approaches are to extend quantitative optical imaging to include depth resolved fluorescence signals in 3 distinct clinical areas:

  • Wound Healing – Cellular activity (NADH/FAD), tissue restructuring and remodeling (Collagen)
  • Photodynamic Therapy (photosensitizer based – fluorescence)
  • Pharmakinetics – Evaluate topical drug delivery and motility

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