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Figure 3 The near-infrared spectral features corresponding to the histologic features of human carotid atherosclerotic plaque. (A) The near-infrared spectra. The dotted line corresponds to the fibrous region; the dashed line to the calcified region; and the solid line to the yellow, soft region. The second derivative was also analyzed (B), thereby reducing the heavy influence of the water signal. The three plaque regions became more homogeneous in signal, but some differences remained, particularly in the region of 1,660 to 1,750 nm. A.U. = absorbance units.