In vivo characterization of human pigmented lesions by degree of linear polarization image maps using incident linearly polarized light.

BACKGROUND AND OBJECTIVE: Melanoma is the most serious form of skin cancer and often appears as an evolving multicolored skin growth. It is well documented that pre-existing atypical or dysplastic nevi can evolve into a melanoma. The development of an in vivo imaging system to characterize benign and malignant nevi has been emphasized to aid in early detection of melanoma. The goal of this study is to utilize a novel Stokes polarimetry imaging (SPI) system for the characterization of pigmented lesions, and to evaluate the SPI system in comparison to dermoscopy and histology images. STUDY DESIGN/MATERIALS AND METHODS: Linearly polarized light with varying incident polarization angles (IPA) illuminated various types of pigmented lesions. The melanocytic nesting patterns of pigmented lesions were characterized by constructing the degree-of-linear-polarization (DOLP) image map with comparison to dermoscopy and histology. The incident polarized light was filtered by visible filters for spectral imaging and incident deeply penetrating red light was used to correlate the SPI image with histopathological examination. RESULTS: The DOLP images with varying IPA at different visible wavelengths were used to characterize various kinds of pigmented lesions by showing subsurface melanocytic nesting distribution as well as morphological information with better resolution and contrast. In correlation with dermoscopy and histology, various defining features such as compound, junctional, lentiginous, reticular, globular patterns of melanocytic nests were identified. CONCLUSION: When imaging pigmented melanocytic lesions, the SPI system with varying IPA at the red light wavelength can better define the melanocytic nesting patterns in both the dermal epidermal junction and the dermis. The SPI system has the potential to be an effective in vivo method of detecting pre-malignant nevi and melanoma.

Stokes polarimetry imaging of rat tail tissue in a turbid medium: degree of linear polarization image maps using incident linearly polarized light.

Illumination with incident linearly polarized light on tissue and polarization state measurements of the remitted light provide a means by which various tissue structures can be differentiated. A rat tail is embedded within a turbid gelatin such that there is a variable depth of medium above it. By varying the incident polarization angle (IPA) of the illuminating linearly polarized light, the geometry, and the orientation angle of the tissue, a series of 2-D degree of linear polarization image maps are created using our Stokes polarimetry imaging technique. The image maps show locations of the polarization-sensitive structures in the rat tail, including soft tissue, intervertebral disks, and tendons. The observed morphologies in the image maps indicate locations where the depolarization of light differs according to the tissue type and underlying layers. The data indicate the importance of varying the IPA, and that tissue dichroism and birefringence affect the degree of linear polarization image maps. Diagnostic information regarding subsurface tissue structures is obtained.

Stokes polarimetry imaging of rat-tail tissue in a turbid medium using incident circularly polarized light.

BACKGROUND AND OBJECTIVES: We describe a Stokes polarimetry imaging technique that quantifies the polarization properties of remitted light backscattered from a sample. STUDY DESIGN/MATERIALS AND METHODS: Right- and left-circularly polarized near-infrared light was used to illuminate rat-tail tissue embedded in turbid gelatin. RESULTS: The degree of linear polarization (DoLP) and degree of circular polarization (DoCP) image-maps indicate that increasing the depth of the rat tail within the turbid medium and varying the rat-tail geometry and orientation relative to the light source affected the contrast between structures and adjacent tissue layers. CONCLUSION: Stokes polarimetry imaging shows that the intervertebral discs and soft tissue regions of rat tails strongly depolarize incident circularly polarized light. Tendon regions remit light with a more linear form due to birefringence. Both DoLP and DoCP image-maps provide contrast between tissue structures. When differentiating between unpolarized light and light with low DoCP or DoLP, the polarization of backscattered light from the turbid medium must to be taken into consideration.