Estimation of the life expectancy of a filament of the conventional X-ray unit: a technical case study.

Conventional diagnostic X-ray units are used for radiographic imaging in several countries. As a part of our quality control procedures, we recorded entrance surface air kerma, tube voltage, and half-value layer measurements for four diagnostic X-ray tubes over a 108 week course. The entrance surface air kerma for one of the X-ray tubes suddenly declined in the 107th week, and the filament burned out 1 week later. We retrospectively reviewed these data and observed that the entrance surface air kerma of the failing tube had increased as a function of elapsed time. The slopes for these four X-ray units were calculated, and we observed that the slope of the failing tube was higher than that of the other three tubes (P < 0.001). Monitoring of the fluctuation in the entrance surface air kerma would be valuable for predicting the residual life expectancy of X-ray tubes.