Multimodal optical imaging and spectroscopy for the intraoperative mapping of nonmelanoma skin cancer

Abstract

Basal cell carcinoma (BCC) is the most common human malignancy, and its incidence increases yearly. In this contribution we investigate the feasibility of combining multimodal reflectance and fluorescence polarization imaging (RFPI) with spectroscopic analysis of the reflectance images for facilitating intraoperative delineation of BCCs. Twenty fresh thick BCC specimens were obtained within 1 h after Mohs micrographic surgeries. The samples were soaked for up to 2 min in an aqueous 0.2 mg/ml solution of methylene blue, briefly rinsed in saline solution, and imaged. Reflectance images were acquired in the range from 395 to 735 nm, with steps of 10 nm. Fluorescence polarization images were excited at 630 nm and registered in the range between 660 and 750 nm. The results yielded by RFPI were qualitatively compared to each other and to histopathology. From the copolarized reflectance images the spectral responses including the optical densities and their wavelength derivatives were calculated. The differences in the spectral responses of the benign and malignant stained skin structures were assessed. Statistical analysis, i.e., Student’s t-test, was employed to verify the significance of the discovered differences. Both reflectance and fluorescence polarization images correlated well with histopathology in all the cases. Reflectance polarization images provided more detailed information on skin morphology, with the appearance of skin structures resembling that of histopathology. Fluorescence polarization images exhibited higher contrast of cancerous tissue as compared to reflectance imaging. The analysis of the optical densities and their wavelength derivatives for tumor and normal tissues has confirmed statistical significance of the differences that can be used for intraoperative cancer delineation. The results of the study indicate that spectral analysis is a useful adjunct to RFPI for facilitating skin cancer delineation.