Patent ID: 7935935

Claim:
An implantable medical device comprising: a radiation-based timer that includes: a radiation source that emits radiation particles during radioactive decay; at least one radiation detection element capable of detecting radiation particles; and a counter that tracks a number of radiation particles detected by the at least one radiation detection element, wherein the radiation-based timer generates a timer signal upon the number of detected radiation particles exceeding a threshold value; at least one other component that uses the timer signal to perform a function; at least one external radiation detection element that detects radiation particles emitted from an external radiation source and does not detect radiation particles emitted from the radiation source of the radiation-based timer; a second timer that generates a second timer signal that is less affected by the external radiation source than the timer signal of the radiation-based timer, wherein the radiation-based timer determines that the timer signal is unreliable based on the external radiation detection element, and wherein the at least one other component does not use the timer signal upon the radiation-based timer determining that the timer signal is unreliable and uses the second timer signal in response to determining the timer signal of the radiation-based timer is unreliable.