Abstract
Fluorescence lifetime provides valuable local metabolic information in tumors embedded in tissue for biodiagnostic applications. We propose performing frequency-domain measurements of fluorescence light propagation to reconstruct maps or images of fluorescence lifetime. We have chosen a multisource and detector arrangement as proposed by Pogue et al.1 that consists of four intensity-modulated sources and twenty detectors on the periphery of the tissue phantom to obtain measurements for input in the developed reconstruction algorithm. The scattering of the light by the tissue makes this problem difficult because the scattering causes loss of spatial correlation of the detected light to the incident light. The image reconstruction involves iterative solution of the forward problem and concomitant update of the lifetime map so as to reduce the least-squares difference between the calculated and observed detector phase and modulation. The forward problem consists of two coupled linear elliptic second-order differential-diffusion equations (that take into account scattering) for excitation and fluorescence fluence in the frequency-domain. These coupled equations are solved for the given boundary and source conditions via the use of a finite-difference multigrid package called MUD-PACK.2 The update of the lifetime map is performed using a Newton-Raphson iterative technique coupled with regularization to account for the ill-conditioned nature of the inverse imaging problem.
© 1996 Optical Society of America
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