An infrared imaging system (10) includes a catheter (11). The catheter is inserted into a small passageway, such as a blood vein (23), in order to collect infrared information from the vein. The information is refracted by at least one lens (32, 46, 52, 57, 63) in a collecting section (17, 45, 56, 61) of the catheter, and is imaged onto the ends (38) of an array of optical fibers (34). The fibers transmit the information to a relay lens (42), which images the information onto respective detector elements of an infrared detector (12). The infrared detector converts the information received from the relay lens into electrical information, which is transmitted to a circuit (13). The circuit generates electrical data that is transmitted to a display (16), which displays a visible image based on the infrared radiation emitted by the scene.