A recent clinical study involved multi-spatial frequency (0.00, 0.15, 0.61, 1.37 mm-1 ), multi-spectral (490, 550, 600, 700 nm) structured light imaging (SLI) of freshly excised, bread-loafed breast conserving surgery tumor specimens. The specimens contained regions of interest (ROIs) of confirmed and homogeneous histological categories of breast tumor tissue determined by expert histopathological analysis. ROIs were sampled into ~4x4mm sub-images before conversion into Gabor filter bank feature vectors. Feature vectors were used in binary, benign-malignant classification scenarios using a support vector machine classifier and 8-fold cross validation. Classification was performed first on feature vectors containing only planar (0.00 mm-1 ) 490 nm monochromatic SLI data. For comparison, a second set of feature vectors from the same sub-images contained the same planar 490 nm illumination data concatenated with high spatial frequency (1.37 mm-1 ) 490 nm monochromatic SLI data. The classification performance of each filter bank was determined for both sets of feature vectors based on receiver operating characteristic (ROC) area under the curve (AUC) values. Gabor filtering and subsequent classification revealed that surface tissue textures exhibited strong rotational dependence and that high spatial frequency surface tissue features were more diagnostic than low spatial frequency surface tissue features. A Gabor filter bank that included 4 relatively high spatial frequencies (0.70-1.98 mm-1 ) and 8 rotation angles (0-157.5°, equally spaced) achieved ROC AUC values <0.9 for 9 of 12 binary tissue subtype classifications.
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