Methods and systems for determining one or more parameters of a tuned circuit forming part of a wireless energy transmission system in an implanted (or implantable) medical device are described. The method involves energizing the tuned circuit then receiving a signal back from it. This signal is then analyzed to determine a property of the circuit such as its quality factor (Q) or resonant frequency. Also described herein is a method and system for determining the implantation depth of a component of an implanted medical device. The method involves determining the position of a magnetic element which is mounted in a fixed physical relationship with the component of the medical device. The methods can be performed on an implanted medical device without the need to explant the device.