Biochemical basis for the difference between normal and atherosclerotic arterial fluorescence.

The observation that laser-induced fluorescence (LIF) spectra of atherosclerotic and normal artery are different has been proposed as the basis for guiding a "smart" laser angioplasty system. The purpose of this study was to investigate the causes of this difference in LIF. Helium-cadmium laser-induced (325 nm) fluorescence was recorded from pure samples of known constituents of normal and atherosclerotic artery including collagen, elastin, calcium, cholesterol, and glycosaminoglycans. Similarities between the LIF spectra of atherosclerotic plaque and collagen and normal aorta and elastin were noted. LIF spectroscopy was then performed on specimens of atherosclerotic aortic plaque (n = 9) and normal aorta (n = 13) and on their extracted lipid, collagen, and elastin. Lipid extraction did not significantly alter atherosclerotic plaque or normal aortic LIF, suggesting a minor contribution of lipid to arterial LIF. The LIF spectra of normal aorta wall was similar to the spectra of the extracted elastin, whereas the LIF spectra of atherosclerotic aortic plaque was similar to the spectra of the extracted collagen. These observations are consistent with the reported relative collagen-to-elastin content ratio of 0.5 for normal arterial wall and 7.3 for atherosclerotic plaque. A classification algorithm was developed to discriminate normal and atherosclerotic aortic spectra based on an elastin and collagen spectral decomposition. A discriminant score was formed by the difference of elastin and collagen (E-C) coefficients and used to classify 182 aortic fluorescence spectra. The mean E-C value was +0.83 +/- 0.04 for normal and -0.48 +/- 0.07 for atherosclerotic aorta (p less than 0.001). Classification accuracy was 92%.(ABSTRACT TRUNCATED AT 250 WORDS)