There are various reasons for a
shift in photopeak. It is best to recognize the differences and correct the problem
immediately. Most equipment is relatively stable once the desired photopeak is identified
and set. Shifts usually occur if there is a problem with the voltage or power supply
to the unit or if the camera is not set precisely on the desired isotopes energy
peak. Tc99m has a photo peak of 140kEv. Similar to tuning into a radio station, if
the camera is set above or below 140kEv the reception will not be clear and pick up
information (noise) from adjacent frequencies or lose information altogether.