a guidance and viewing system based on multiplexed optical coherence domain reflectometry is incorporated into a catheter , endoscope , or other medical device to measure the location , thickness , and structure of the arterial walls or other intra - cavity regions at discrete points on the medical device during minimally invasive medical procedures . the information will be used both to guide the device through the body and to evaluate the tissue through which the device is being passed . multiple optical fibers are situated along the circumference of the device . light from the distal end of each fiber is directed onto the interior cavity walls via small diameter optics . both forward viewing and side viewing fibers can be included . the light reflected or scattered from the cavity walls is then collected by the fibers and multiplexed at the proximal end to the sample arm of an optical low coherence reflectometer . the system may also be implemented in a nonmedical inspection device .