What happens when X-ray tubes are ageing?

Quality assurance (QA) tests are first done to establish measurement references (acceptance testing), and thereafter serve to uncover possible malfunctions or wear and tear problems in the X-ray machine over time (constancy testing).

There are several likely problems which might occur and could effect performance which regular quality assurance testing can detect at an early stage.

Every time X-ray is produced, the cathode filament will lose some atoms. Over time, it becomes thinner and thinner until it eventually breaks. This may affect image resolution negatively. For that reason, X-ray machines need to have their filament current adjusted from time to time.

Moreover, the metal from the vaporized anode and filament will be deposited on the inside of the X-ray tube, causing the glass to blacken over time. This can affect the X-ray beam quality (e.g. the HVL may increase). It can deteriorate the image contrast and may even cause the X-ray tube to break. The anode will also suffer from wear and tear with use and may become rougher, affecting the radiation quality.