Arterial bifurcations are commonly the sites of developing atherosclerotic plaque that lead to arterial occlusions and plaque rupture (myocardial infarctions and strokes). The composition of atherosclerotic plaque is heterogeneous, even within the same individual, reliable morphometric information and a way of characterizing composition is clinically desirable. Laser induced fluorescence (LIF) spectroscopy provides an effective nondestructive method supplying spectral information on extracellular matrix (ECM) protein composition, specifically collagen and elastin. Our purpose is to investigate regional differences in the ECM proteins -- collagen I, III and elastin in unstable plaque by analyzing data from laser-induced fluorescence spectroscopy of human carotid endarterectomy specimens. Gels of ECM protein extracts (elastin, collagen types I & III)
were measured as reference spectra and internal thoracic artery segments (extra tissue from bypass surgery) were used as tissue controls. Arterial segments and endarterectomy specimens were cut into cross-sectional rings. 10 spectra per sampling area were recorded and normalized to peak intensity. Tissue rings were fixed in formalin (within 3 hours of surgery), sectioned and stained with H&E or Movat's Pentachrome for histological analysis. Spectroscopy data were correlated with immunohistology (staining for elastin, collagen types I, III and IV). Optical analysis of the control artery (internal thoracic artery), a composite tissue, revealed a predominant elastin fluorescence component -- confirmed with immunohistology. Diseased specimens by comparison had decreased elastin and a significant (p<0.05) elevation of collagen types I and III. Fluorescence spectroscopy is an effective method for evaluating ECM (collagen and elastin) associated with vascular remodeling despite the considerable variability in the plaque structure. Consistent regional differences were detected in the carotid specimens.