Abstract: Systems and methods for locating invasive intravascular devices within a vascular system are provided. In one embodiment, an invasive medical sensing system is disclosed. The system comprises a flexible elongate member having a plurality of radiation-sensitive components arranged around an outer circumferential surface of the flexible elongate member. The plurality of radiation-sensitive components is arranged such that an orientation of the flexible elongate member can be determined when the sensors are exposed to radiation produced by a radiation source. The system further comprises a watchdog component communicatively coupled to the plurality of radiation-sensitive components and operable to detect radiation-induced changes in behavior of the plurality of radiation-sensitive components caused by the radiation and to determine the orientation of the flexible elongate member relative to the radiation source based on the detected radiation-induced changes in behavior.