Time-resolved laser-induced fluorescence of arterial wall constituents: deconvolution algorithm and spectrotemporal characteristics

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Abstract
In this study, we had two objectives: (1) to develop an algorithm based on the Laguerre expansion of kernels technique for deconvoluting time-resolved fluorescence spectra; (2) to characterize the time-resolved emission of elastin and collagen, substances present in different amounts in healthy and diseased arterial wall. The transient fluorescence of purified samples excited with a Nitrogen laser pulse (3 ns) was measured at different wavelengths with an MCP-PMT and digitized at 2 Gsample/s. The deconvolution algorithm expressed the impulse response function as a weighted sum of Laguerre functions. We found that five Laguerre functions were sufficient to represent the fluorescence impulse response function for both substances. A fast-decay and a slow-decay components were identified in the impulse response function. The slow decay increased with the wavelength of emission ((lambda) ) for elastin (p < 0.05) whereas it decreased with (lambda) for collagen. The fast decay was independent of (lambda) for elastin and decreased with (lambda) for collagen. The fluorescence impulse response function can be retrieved even when the duration of the excitation pulse is in the range of the fluorescence lifetime. The dynamics of the temporal emission of collagen and elastin varies with the wavelength of emission suggesting that using temporally-resolved fluorescence spectra would improve optical analysis of the arterial wall.

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