A flexible catheter includes an elongated body, and a sensor. The elongated body has proximal and distal end portions and defines a working channel therethrough. The sensor is disposed in the distal end portion of the elongated body and is adapted for detecting the position of a distal end of the elongated body within the anatomy of a patient. The sensor is formed from a wire that forms a first layer of wraps about the distal end portion of the elongated body and that includes first and second leads that form a twisted pair proximal to the first layer of wraps. The twisted pair of the first and second leads extends to the proximal end portion of the elongated body.