Optical coherence tomography (OCT), a non-invasive medical imaging technology that uses non-ionizing radiation, has the potential to provide cellular level resolution in a system that is clinically viable, highly affordable, and portable. OCT is a recent development in medical imaging technology that has resulted in laboratory demonstrations of image resolution comparable to that of histology. However, due to their size, cost, and unreliability, these laboratory systems cannot be made into clinically viable systems. Further, because of their output wavelength, they have been limited to image depths of 0.5 mm. This proposed NIH Phase I STTR will result in a laser source capable of cellular level resolution to a depth of 3 mm in non- transparent tissue. This source will be integrated into an existing OCT system at Wellman Laboratory for Photomedicine, and imaging will be performed on excised tissue from the human gastrointestinal tract. These images will be correlated with subsequent histological examination. While the laser source to be developed on this Phase I program will not itself be clinically viable, we will perform a design study of a novel laser cavity design that will meet all of the requirements of a clinically viable OCT imaging system with cellular level resolution. PROPOSED COMMERCIAL APPLICATION In clinical studies being conducted at Wellman Laboratory for Photomedicine, OCT is providing real time images that are being used to guide excisional biopsies in the esophagus. By providing micron level guidance, OCT offers the potential for a dramatic reduction in sampling errors associated with blind biopsies. At higher resolution, OCT also holds the potential to eliminate the need for excisional biopsy altogether by providing the ability to perform an "optical biopsy". Optical biopsy could have important applications in dermatology, gastroenterology, cardiology, otolaryngology, dentistry, pulmonology, gynecology and urology.