Abstract: An electro-optic, noncontact, interior cross-sectional profiler (a "probe") and method of using the probe to determine the physical characteristics, such as interior dimensions, of an interior surface of a tubular structure, such as pipe, tubing, gun barrels and the like. The probe utilizes a disc of unfocused light to illuminate a cross-section of the interior surface and images the illuminated cross-section from the interior surface to a photodetector array, where the image can be evaluated. The probe is useful for off-line and on-line (or "in-line") processes, such as an extrusion process.