Described herein is a sensing wire for locating a blood vessel in a patient. The sensing wire comprises a hollow, rigid tube including a lumen extending from a proximal portion to a distal portion, an ultrasonic sensor coupled to the distal portion of the tube, and a communication assembly positioned at the distal portion and coupled to the ultrasound sensor. Also described is a system for accessing and evaluating a blood vessel in a patient. The system comprises an access sensor wire, an access needle sized to receive the access sensor wire, and a second sensing wire configured to be positioned within the access needle. A method is also disclosed for accessing a blood vessel with an introduction needle, where a short access sensing wire is replaced by a much longer second sensing wire after the needle is positioned in the vessel.
