In vivo MPM imaging using a miniaturized endoscope. A, Photograph of the flexible multiphoton endoscope (green dotted rectangle) used in this study on an optical table, held by an articulating arm. B–C, Infrared CCD camera images of the endoscope while imaging the surgically exposed colonic mucosa of a live, anesthetized rat, at 2x (B) and 10x(C) magnifications. The endoscope is outlined by green dotted rectangles and the rat colon is indicated by the arrows. D, Image of the colonic mucosa of a living rat generated with the flexible MPM endoscope shown in A–C. This unaveraged single image frame shows a field of view of 1153m X 1153m was acquired at 4.1 frames/sec using 75 mW incident power at 800 nm. E, Image of an ex vivo section of rat colon, acquired using the bench-top Olympus MPM system at identical dimensions and a comparable focal depth as the endoscope. F, H&E-stained section of the same colon imaged by MPM in panel E. Colonic crypts indicated by “*”, enterocytes indicated by arrows and goblet cells indicated by arrowheads.