Abstract: A method of positioning a catheter, for example a balloon or treatment catheter. The catheter is inserted in a passage and sensed through the luminal wall to correctly determine its position. As applied to prevent hemorrhage during surgery the method involves inserting the catheter in a deflated configuration along a passage such as a blood vessel near to the operative site in a position determined by direct or video-assisted sensing from outside the passage. In the event a blood vessel is cut during surgery, the already-positioned catheter inflates a balloon to occlude the passage and stop blood flow into the injured site. In one aspect, a flow-directed catheter includes an inflatable balloon attached at its distal end and an optical fiber connected to one or more light emitting regions positioned at the tip or in the vicinity of the balloon.