Characterization of atherosclerotic lesions with laser-induced time resolved fluorescence spectroscopy

The time-dependent decay of arterial wall fluorescence remains relatively unexplored. We measured the time-resolved fluorescence emission (337 nm excitation) of 37 excised samples of human aorta classified histologically as normal or Type I-Type Va atherosclerotic lesion (Stary's classification). Time-resolved spectra (370-510 nm, 0.5 ns temporal resolution) were constructed by deconvoluting the emission waveform using the discrete-time Laguerre basis for expansion of the decay. The spectra changed markedly with tissue type, being spectrally broad for normal samples and peaked for atherosclerotic samples. In the time dimension, the emission lasted longer for the atherosclerotic samples. Biexponential approximation of the fluorescence time-dependent decay (390 nm) showed that the long decay constant for Type II lesions (5.95+/-3.16 ns) was larger than the corresponding parameter for normal arterial wall (5.42+/-0.17 ns) and smaller than the decay constant for intermediate (Type III) and advanced (Types IV-Va) lesions (6.88+/-0.32 ns, 7.38+/-0.51 ns). Discriminant analysis using the time constants at 390 nm and the intensity ratio I 390/I 470 as predictor variables classified near-normal (normal-Type I) and diseased samples (Types III-V) with > 90% sensitivity. 75% of Type II lesions were correctly classified. These results suggest that atherosclerotic lesions can be accurately classified based on their time-resolved fluorescence spectra.