A guidewire for a medical device is disclosed. The guidewire includes an elongate body, a proximal connector assembly, a corewire, and a sensor assembly. The body has an annular wall that defines an interior lumen. The proximal connector assembly is coupled to the body and is configured for connection to a medical positioning system. The corewire extends through the lumen. The sensor assembly located on a distal end of the corewire is electrically connected to the proximal connector assembly. The sensor assembly is configured to generate an electrical signal indicative of a position of the sensor assembly in a reference coordinate system defined in the medical positioning system. The body includes a helical cutout extending over a predetermined length of the body. The helical cutout is configured to increase the flexibility over the predetermined length of the body.