A polarization-enhanced wide-field imaging device was used to assess tumor margins on a macroscopic scale. A schematic of the system is presented in Fig. 1(a). The system has been described in detail elsewhere.18,19 In short, a xenon arc lamp (Lambda LS, Sutter, Novanto, CA) combined with nine narrow bandpass filters, with full width at half maximum of 10 nm, that covered wavelength ranges from 390 nm to 750 nm was used as an illuminator. A Rodenstock lens coupled to a CCD camera (CoolSnap Monochrome Photometrics, Roper Scientific, Tucson, AZ) was used for image acquisition. Linearly polarizing filters (Meadowlark Optics, Frederick, CO) were employed in pathways of the light incident on the sample and light collected by the camera. Reflectance co- and cross-polarized images were acquired at the selected wavelengths (, 440 nm, 500 nm, 577 nm, 600 nm, 620 nm, 640 nm, 680 nm, 750 nm). Fluorescence co-polarized and cross-polarized images were excited at 640 nm and registered between 660 nm and 750 nm using an additional bandpass filter (660AELP, Omega Optical, Brattleboro, VT) placed in the pathway of the light remitted from the specimen. Co- and cross-polarized images were registered with an analyzing polarizer oriented parallel (co) and perpendicular (cross) to the polarization of the incident light. In the described configuration, the system allowed for a field of view of , and a lateral resolution of approximately 30 μm. The wide-field imaging of one sample required less than 3 min. For accurate detection of the two orthogonally polarized components of reflectance and fluorescence, the system was calibrated as described by Lakowicz.28 The calibration factor, , was determined to be 0.98.