Abstract
Skin cancer is the most common type of cancer, and its detection relies heavily on visual observation. The goal of this research is to aid in the progress of developing a non-invasive optical biopsy based on endogenous fluorescence and non-linear light scattering that can be used to detect skin cancer. A trial was conducted that followed 30 UV- and sham-exposed SKH1 mice over a 6-month period. Collagen images were obtained by using second harmonic generation. In this process pulsed 740 nm Ti:sapphire laser light was incident on the collagen in the mouse's dermis where two photons were converted into a single photon that had twice the energy. We were able to collect and spatially resolve the light that was emitted by using a confocal detector allowing us to obtain collagen images. A stack of images obtained with a variable confocal aperture were acquired so that we could measure the forward to backward (F/B) ratio of the SHG light. This measurement gives a way to quantify the light scattering by collagen fibers that are present within the skin and can be used as a diagnostic tool.
Over the duration of the experiment, protocols were developed and implemented for imaging SKH1 mice. Collagen images were analyzed to measure the F/B ratio. The measured F/B ratios were compared across treatment groups and sex. The F/B ratios for male mice were higher than female mice. The results also showed that sham-exposed female mice had a higher F/B ratio than UV-exposed female mice. However, sham-exposed male mice had a slightly lower F/B ratio than UV-exposed male mice. On one day, two SHG stacks were acquired in the same mouse in different tissue types. One of the locations was in an area of cancerous tissue and the other was in healthy tissue. When these two SHG stacks were compared, it was found that the F/B ratio for the area of cancerous tissue was significantly lower than that of the healthy tissue. While these results are promising, more experiments need to be conducted comparing the F/B ratio in cancerous tissue with healthy tissue in the same mouse.