To summarize, our setup has proven its ability to image biological tissues ex vivo and reveal fine tissue structures thanks to its micrometer-scale resolution. Preliminary in vivo experiments on skin give promising results. The design of our probe, allowing diameters ranging from less than 1 mm to a few mm, makes it suitable for in situ imaging of different accessible areas.
However several points still have to be improved for future development of a medical device. In this work the acquisition time of one 2-D image was typically 1 second, but we plan on reaching a frequency of several Hz. This can be done by acquiring a more powerful light source and a faster 2-D camera, and by improving the mechanical setup to increase the sensitivity of the system, thus reducing the number of accumulations needed to have a good image quality. Another limitation of our current setup is that although the imaging depth can be easily scanned through the tissue, the focal depth stays fixed at a given depth. The imaging range is therefore limited by the depth field of the probe optics. Since it is typically 50 µm we were only able to image tissues up to depths around 100 µm. However we could introduce dynamic focusing relatively easily thanks to the use of GRIN lenses. Indeed one can displace the focal plane at the exit of a GRIN lens by displacing the focal plane at the entrance, for example using a microscope objective or lens system mounted on a linear motor. Such a system has already been previously described by other groups [19
]. Finally, the current bulk setup has to be designed into a hand-held probe in order to be able to access areas of interest on the patient’s body. A hand-held probe could then be used in dermatology for imaging of the skin, but it could also guide the surgeon during tumor removal operations and guide biopsy procedures, for example in the breast.
In the meantime this system could also be implemented with a flexible probe based on a fiber bundle. In comparison with the rigid probe the image quality would be degraded due to the pixelation effect of the fibers, but a system with a flexible probe would allow for imaging of areas inaccessible with the rigid probe. It could for instance be used in the aero-digestive and gastrointestinal tracts.
We believe in vivo and in situ applications of FFOCT for endoscopic evaluation could be very crucial for the clinician and the surgeon. It could allow the clinician to better evaluate the nature of the lesion he has discovered and to choose the field of mucosa he has to biopsy for conventional morphologic diagnosis or ancillary diagnosis techniques in the screening of bronchus cancer as well as colon or gastric cancer, cervical uterus cancer, or vesicle cancer. Also during coelioscopy or thoracoscopy for example, the surgeon has not the ability to palpate directly with the hand the tissue and to appreciate the induration related to an eventful neoplasm. Our minimally invasive technique could improve the appreciation of the surgeon.