Determination of the cholesterol–collagen ratio of arterial atherosclerotic plaques using near infrared spectroscopy as a possible measure of plaque stability

Particular danger associated with an arteriosclerotic plaque consists in the possible rupture of its cap, dependent on the thickness of the cap covering the lipid core, its composition and different inflammatory changes. The purpose of this study was to compare the total cholesterol and collagen contents of arterial walls, both measured by near infrared spectroscopy (NIRS), and to test whether the ratios of cholesterol to collagen correlate with histochemical parameters possibly being indicators for plaque stability. NIR spectra of 118 sections from 36 human aortas were measured at 1000–2500 nm. Evaluation was performed by the partial least squares method (PLS), the chemical reference analysis by HPLC. Acceptable results were achieved for calibrations. With these calibrations 38 further aortic sections taken at autopsy were NIR-spectroscopically analysed and ordered in relation to histological findings of fatty deposits, cap thickness over the lipid core, and the ratio of fatty deposits to cap thickness. Correlations were found to exist between the spectroscopically determined total cholesterol concentrations and the histologically estimated fatty deposits (r=0.887), between the spectroscopically determined collagen concentrations and the cap thickness over the lipid core (r=0.441), and between the ratios total cholesterol to collagen and the ratios fatty deposits to cap thickness (r=0.575).