Global analysis of arterial fluorescence decay spectra

Global analysis of time-resolved fluorescence measured at multiple emission wavelengths was applied to simulated fluorescence spectra and arterial fluorescence spectra. Fluorescence of human aortic samples was produced with nitrogen laser excitation. Simulated spectra had decay characteristics in the range expected from previous studies of artery tissue. For both types of spectra, the emission decay was analyzed with global analysis to model the decay with a sum of exponentials. Decay constants were held fixed across wavelengths while pre-exponential coefficients were wavelength-dependent. For the simulated spectra, global analysis was compared to the traditional method in which decay constants and pre-exponential coefficients are assumed wavelength-dependent. On the simulated data, three decays could be reliably estimated by global analysis even when only two exponential decays were identified with the traditional method. On the arterial data, the intermediate decay and the long decay significantly increased between normal samples and fibrous plaque (1.7 to 2.5 ns; 7.0 to 8.4 ns). The pre-exponential coefficient of the long decay was larger in the blue range of the spectrum for the samples with advanced atherosclerosis. We conclude that global analysis markedly improves the recovery of exponential decay trends in time-resolved fluorescence spectra. Application to artery tissue fluorescence reveals characteristic spectral changes associated with atherosclerosis.