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 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.
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.
Dye-assisted photothermal welding is a technique used to close wounds by thermally cross-linking collagen across apposed tissue edges. For a successful weld, not only do laser parameters have to be optimized, but also apposition of the incision has to be consistent and controlled. The objective of this study was to quantify the relationship between the applied apposition pressure (i.e., the compressive force holding the wound closed during the welding procedure divided by the area of the skin-to-skin interface) and the tensile strength of the wound following the welding procedure. By using a clamping device made of two complementary pieces, each 3 cm wide with a row of 10 equally spaced blunt wire mesh tips, the apposition pressure along a 2-cm-long incision in each albino guinea pig was quantified using a 127-µm-thick load cell and varied from 0-1.8 kgf/cm 2 . A continuous wave, Nd:YAG laser emitting 10.0 W of 1.06-um radiation from a 600-µm-diameter fiber irradiating a 5-mm-diameter spot size was scanned across the incision in order to deliver 300 J of total energy. As the apposition pressure of the incisions was increased, the resulting tensile strength of welded skin increased in a sigmoidal manner. For this welding technique, an apposition pressure of at least 1.2 kgf/cm 2 is necessary to obtain maximum weld strength of the skin (2.56 ± 0.36 kg/cm 2 ).
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