IMAGING OF FLUORESCENT YIELD AND LIFETIME FROM MULTIPLY SCATTERED-LIGHT REEMITTED FROM RANDOM-MEDIA

The feasibility of employing fluorescent contrast agents to perform op tical imaging in tissues and other scattering media has been examined through computational studies. Fluorescence lifetime and yield can giv e crucial information about local metabolite concentrations or environ mental conditions within tissues. This information can be employed tow ard disease detection, diagnosis, and treatment if noninvasively quant itated from reemitted optical signals. However, the problem of inverse image reconstruction of fluorescence yield and lifetime is complicate d because of the highly scattering nature of the tissue. Here a light propagation model employing the diffusion equation is used to account for the scattering of both the excitation and fluorescent light. Simul ated measurements of frequency-domain parameters of fluorescent modula ted ac amplitude and phase lag are used as inputs to an inverse image- reconstruction algorithm, which employs the diffusion model to predict frequency-domain measurements resulting from a modulated input at the phantom periphery. In the inverse image-reconstruction algorithm, a N ewton-Raphson technique combined with a Marquardt algorithm is employe d to converge on the fluorescent properties within the medium. The suc cessful reconstruction of both the fluorescence yield and lifetime in the case of a heterogeneous fluorophore distribution within a scatteri ng medium has been demonstrated without a priori information or withou t the necessity of obtaining absence images. (C) 1997 Optical Society of America.