Demarcation of nonmelanoma skin cancer margins in thick excisions using multispectral polarized light imaging

More than a million cases of nonmelanoma skin cancers are diagnosed every year. Treatment of cancer patients could benefit greatly if a real-time, noninvasive, reliable, and cost-effective technique for delineating tumor margins were available. A novel multispectral dye-enhanced polarized light imaging technique that enables rapid imaging of large tumor fields is described. A tunable monochromatic light source and a CCD camera were employed as the imaging device. Linear polarizers were introduced into both the incident and collected light pathways in order to limit the measurement volume to the superficial tissue layers. To enhance the tumor contrast in the image, aqueous solutions of toluidine blue or methylene blue were topically applied to fresh thick skin excisions for several minutes. Then the specimens were rinsed in saline solution. Images were acquired before and after staining at the selected wavelengths. The two sets of wavelengths corresponding to the hemoglobin Soret absorption band and to the absorption bands of the dyes were used to demarcate the areas of enhanced hemoglobin and dye absorption, respectively. The resulting images demonstrate that staining significantly enhances contrast of the tumor in the image and enables reliable delineation of cancer. Locations and shapes of tumor lobules revealed by polarized light images closely correspond to those found in Mohs frozen sections for 41 specimens out of 45. The study demonstrates that the suggested technique has significant potential as a guidance tool in tumor excision surgery.