A timing source for a pulse generator is disclosed, which timing source includes an input for receiving a reference clock output at a reference operating frequency. The apparatus further comprises a cover for enclosing the magnetic sensor. The detachable filling element and the radioactive source are adapted to be inserted into a vessel at least in close proximity of a neck of an aneurysm. Temperature meters may measure the temperatures for each of the flows to maintain consistency. The electronic circuit includes a transmitter to transmit measurement data from the sensor to the remote system.