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Figure 5 Cluster analysis yields an empiric classification of the NIR reflectance spectra of fresh atherosclerotic plaques from 25 patients. The plaques were divided into 145 fresh (living, unfixed) specimens and examined by near-infrared reflectance spectroscopy. Cluster analysis reveals three distinct groups (right panels) in each of two spectral regions: 2,240 to 2,320 nm (A) and 1,665 to 1,800 nm (B). For each of the six cluster groups (right panels), an average spectrum was calculated (A and B). Group 1 specimens in the top and bottom panels correspond to American Heart Association (AHA) type I and II stable lesions. Group 2 specimens correspond to AHA type III and IV lesions. Group 3 specimens correspond to AHA type V and VI lesions.