Fig. 2.

Illustration of principal components for diffuse reflectance measurements. The first three principal components in order of net variance corresponding to the diffuse reflectance spectra acquired from the freshly excised breast tissue cores. PC1 and PC2 both demonstrate oxy-hemoglobin absorption features, namely the Soret band at 414 nm, and the Q bands at ca. 547 and 580 nm, with a shallow absorption trough at 563 nm. PC3 shows a wider trough in the 430–490-nm region, which contains β-carotene absorption features (typically at 450 and 480 nm).