Lesion composition plays a significant role in atherosclerotic lesion instability and rupture. Current clinical techniques cannot fully characterize lesion composition or accurately identify unstable lesions. This study investigates the use of time-resolved fluorescence spectroscopy for unstable atherosclerotic lesion diagnosis. The fluorescence of human coronary artery samples was induced with nitrogen laser and detected in the 360-to 510-nm wavelength range. The samples were sorted into 7

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... ps according to the AHA classification: normal wall and types I, II a (fatty streaks), III (preatheroma), IV (atheroma), V a (fibrous), and V b (calcified) lesions. Spectral intensities and time-dependent parameters [average lifetime f ; decay constants: 1 (fast-term), 2 (slow-term), A 1 (fast-term amplitude contribution)] derived from the time-resolved spectra of coronary samples were used for tissue characterization. We determined that a few intensity values at longer wavelengths (Ͼ430 nm) and time-dependent parameters at peak emission region (390 nm) discriminate between all types of arterial samples except between normal wall and type I lesions. The lipid-rich lesions (more unstable) can be discriminated from fibrous lesions (more stable) on the basis of time-dependent parameters (lifetime and fast-term decay). We inferred that features of lipid fluorescence are reflected on lipid-rich lesion emission. Our results demonstrate that analysis of the time-resolved spectra may be used to enhance the discrimination between different grades of atherosclerotic lesions and provide a means of discrimination between lipid-rich and fibrous lesions. (Arterioscler Thromb Vasc Biol. 2001;21:1244-1250.)