Two steady-state methods for localizing a fluorescent inhomogeneity in a turbid medium

Thomas H. Foster, Edward L. Hull, Michael G. Nichols, David S. Rifkin, Nina Schwartz

Research output: Contribution to journalConference articlepeer-review

5 Scopus citations


We present two cw methods for localizing a source of fluorescence buried in a medium with optical properties similar to those of tissue in the near infrared region. The first approach is based on the fact that, for small excitation beam diameters, the absolute intensity at a given depth in the medium depends on the diameter of the incident beam. For a well-chosen pair of beam diameters, the ratio of these intensities in a scattering medium depends uniquely on the depth from the surface of incidence. Thus, the ratio of the fluorescence resulting from sequential excitation using two beam diameters can be used to determine the depth at which the fluorescence originated. The second method is based on spatially resolved surface measurements of the diffuse fluorescence from the buried source. Using a form of the diffusion theory analysis of Farrell et al. (Med. Phys., 1992) for the spatially resolved diffuse reflectance from a pencil beam incident on a scattering medium, it is possible to reconstruct the depth of the source from the shape of the surface fluorescence profile. Preliminary experimental results obtained using a 1.0 cm diameter sphere containing the tumor localizing fluorophore Nile Blue A show that the spatially resolved measurement reports the location of fluorescent sources as deep as 4.0 cm with an accuracy of 0.4 cm or better.

Original languageEnglish (US)
Pages (from-to)741-749
Number of pages9
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Dec 1 1997
Externally publishedYes
EventProceedings of Optical Tomography and Spectroscopy of Tissue: Theory, Instrumentation, Model and Human Studies II - San Jose, CA, United States
Duration: Feb 9 1997Feb 12 1997

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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